Category 6™

Joaquin Approaching Bahamas; Possible U.S. Landfall This Weekend

By: Jeff Masters and Bob Henson , 9:14 PM GMT on September 30, 2015

Hurricane Joaquin is developing into a formidable storm as it churns over record-warm waters east of the Bahamas. Top sustained winds in Joaquin were 85 mph as of the 5:00 pm EDT advisory from the National Hurricane Center (NHC), and the central pressure had dropped to 967 millibars. Joaquin's center was located roughly 175 miles east-northeast of the central Bahamas. A large, distinct eyewall was evident on Wednesday morning imagery from microwave imagery and from visual observations from an Air Force hurricane-hunter aircraft. An eye was intermittently apparent on visible satellite imagery by early Wednesday afternoon, although the eye remained largely obscured by clouds. Infrared imagery showed an enlarging shield of showers and thunderstorms (convection) around Joaquin's core. Northwesterly wind shear was still limiting the amount of outflow on Joaquin's north side, but the shear appears to be slowly relaxing.


Figure 1. Enhanced infrared image of Hurricane Joaquin, collected at 1915Z (3:15 pm EDT) Wednesday, September 30, 2015. Image credit: NOAA/NESDIS.

With its continued fairly slow motion (only 8 mph) toward the southwest, Joaquin remains on a track somewhat further south than earlier expected. Hurricane warnings are now up for the central and northwestern Bahamas, with a tropical storm warning for the southeastern Bahamas. Joaquin is expected to move very slowly over the central Bahamas over the next two days, before embarking on a much more rapid northward track on Friday that will take it safely away from the Bahamas.


Figure 2. GOES 13 image of Hurricane Joaquin approaching the Bahamas as seen on Wednesday, September 30, 2015, at 9:15 am EDT. At the time, Joaquin had top winds of 75 mph. Image credit: NOAA Visualization Lab.

Impact of Joaquin on the Bahamas
Winds were rising across the Central Bahamas on Wednesday afternoon, and were a brisk 31 mph, gusting to 37 mph, at  2:34 pm EDT at a personal weather station on Exuma Island. Shemp's Webcam from Exuma Island on Wednesday afternoon showed a steady increase in clouds, and in whitecaps on the waters, as Joaquin approached.

Joaquin's main threat to the Bahamas is likely to be wind damage. The 5 pm Wednesday Wind Probability Forecast from NHC gave the highest chances of hurricane-force winds of 62% to San Salvador Island (population 930). Hurricane-force winds are slightly less likely on Cat Island (population 1,500), to the northwest of San Salvador Island. Heavy rains of 10 - 20 inches in the Central Bahamas may also cause damage, as well as the large waves of the storm riding up on top of the expected 2 - 4' storm surge. The latest 8 am EDT (12Z) Wednesday run of the GFS model portrays the center of Joaquin passing over San Salvador Island around 2 pm EDT Thursday. Tropical storm-force winds of 39+ mph have likely already begun on the island, so they are in for a long battering. More concerning for the Central Bahamas is the latest 12Z Wednesday forecast from the European model, which has Joaquin penetrating about 70 miles farther to the southwest, stalling out over Exuma Island on Thursday night.


Figure 3. This Maximum Water Depth storm surge image for the Bahamas shows the worst-case inundation scenarios for a Category 2 hurricane with 105 mph winds, as predicted using dozens of runs of NOAA's SLOSH model. For example, if you are inland at an elevation of ten feet above mean sea level, and the combined storm surge and tide (the "storm tide") is fifteen feet at your location, the water depth image will show five feet of inundation. No single storm will be able to cause the level of flooding depicted in this image. The regions of the Bahamas most vulnerable to storm surge tend to lie on the southwest sides of the islands. Since Joaquin is approaching from the northeast, the storm's peak on-shore winds will be affecting the northeast sides of the islands, where deeper offshore waters tend not to allow larger storm surges to build. NHC is forecasting peak water levels (the depth of water above the high tide mark) of 2 - 4 feet from Joaquin in the Bahamas. See wunderground's storm surge pages for more storm surge info.

Hurricane history for the Bahamas
The last hurricane to affect the Bahamas was Hurricane Sandy of 2012, which passed through the Central Bahamas as a Category 2 storm with winds of up to 105 mph. Sandy caused two deaths and damage estimated at $703 million, equivalent to 9% of the nation's GDP. The most severe damage was on Cat Island and Exuma, due to wind and storm surge. According to EM-DAT, the most expensive hurricane in Bahamian history was Category 4 Hurricane Frances of 2004, with damages estimated at $1 billion.

Where will Joaquin go after the Bahamas?
Joaquin is trapped to the south of a high pressure system whose clockwise flow will push the cyclone very slowly to the southwest or west-southwest at about 3 - 6 mph. As the storm progresses to the southwest, the strong upper-level winds out of the north currently bringing high wind shear of 20 knots will gradually decrease, allowing Joaquin to strengthen. The 2 pm EDT Wednesday run of the SHIPS model predicted that wind shear over Joaquin would fall to the light to moderate range, 5 - 20 knots, on Thursday and Friday. These conditions should allow Joaquin to intensify to a Category 2 hurricane, and possibly a major Category 3 hurricane, by Friday. As Joaquin progresses to the west, the storm will also increasingly "feel" the steering influence of a strong upper-level trough of low pressure situated over the Eastern United States.


Figure 4. The operational GFS and ECWFM model runs from 12Z Wednesday, September 30, offer wildly differing projections for Hurricane Joaquin for 12Z (8:00 am EDT) Sunday, October 4. Image credit:Levi Cowan, www.tropicaltidbits.com, via Phil Klotzbach.

The big trend from the 00Z Wednesday suite of computer model guidance was a marked convergence among models toward a landfall in the vicinity of North Carolina or Virginia. Among the major dynamical models, only the ECMWF remained adamant that Joaquin would head to sea well before reaching the southeast U.S. Little had changed in the 12Z Wednesday round, as the non-ECMWF models (GFS, HWRF, GFDL, UKMET) were heavily clustered around a potential landfall in or near North Carolina on Saturday or Sunday while the ECMWF kept Joaquin well out to sea at the same point.


Figure 5. The operational ECMWF (top) and GFS (bottom) model runs from 0Z Wednesday, September 30, showed similar depictions of the eastern U.S. trough steering Joaquin, but much different depictions of an intensifying upper-level trough east of Newfoundland. This may help explain why the ECMWF operational model is taking Joaquin out to sea. Image credit: Ben Papandrea, WSI.


Why the discrepancy between the ECMWF and other models? The leftward hook prominently featured in the other models is being driven by the increasingly negative tilt (NW-to-SE) to the upper trough deepening over the eastern U.S. late this week. The models are projecting that this trough would pull in Joaquin on its northeast side, in much the same way that a strong upper-level low did with Hurricane/Superstorm Sandy in 2012, although in this case the process would unfold a couple of hundred miles to the south. The ECMWF run shows a very similar upper-level pattern to the other models across the eastern U.S., but Joaquin's interaction with the trough occurs later in the ECMWF, giving the hurricane a chance to escape some of the trough's influence. Another feature of interest is an upper-level low east of Newfoundland, which is depicted as being much stronger in the GFS than in the ECMWF (see Figure 5 at right). This low is associated with increased ridging in the Northwest Pacific that would help shunt Joaquin into the U.S. East Coast, in tandem with the eastern U.S. upper trough.

Back in 2012, the ECMWF model caught on to the leftward hook of Sandy's track several days before other models. The ECMWF's high overall skill means we cannot entirely discount its out-to-sea forecast for Joaquin just yet. At the same time, the strong consistency among other leading models in projecting a landfall in or near North Carolina cannot be ignored. We can gain more perspective on the mid-Atlantic scenario by looking at the ECMWF and GFS ensemble output from 00Z Wednesday. In each ensemble, the model is run a number of times for the same situation, but with the starting conditions varied slightly to represent the uncertainty in our starting-point observations of the atmosphere. The ECMWF and GFS ensembles from 00Z Wednesday are much more similar in flavor than you might expect from looking at their single operational runs. Both models have a majority of ensemble members heading for the U.S. East Coast, with a few outliers heading to sea.

What kind of U.S. impacts could Joaquin bring?
A hurricane watch could be required for portions of the U.S. East Coast as early as Thursday night, and NHC is now citing the possibility of a major hurricane landfall in the Carolinas. If Joaquin moves along the track projected by most models, hurricane-force winds could arrive somewhere on the NC/Mid-Atlantic coast over the weekend. Very high seas and a significant storm surge could also be expected. It is relatively rare for a hurricane to make a Sandy-like left hook into the U.S. East Coast. Such a track was unprecedented for New Jersey in hurricane annals, and even in the NC/VA area, it is uncommon enough that the likely effects would be both unusual and high-impact. The closest analogue from recent years is 2003's Hurricane Isabel. Isabel brought a major storm surge into the Chesapeake Bay and nearby waterways, plus widespread impacts from high wind and heavy rain. Such an outcome would depend heavily on the exact track of Joaquin. Storm surge expert Dr. Hal Needham of LSU has a detailed look at the potential for storm surge from Joaquin along the U.S. East Coast in his Wednesday morning blog post, Widespread Storm Surge Event to Impact U.S. Atlantic Coast.

Regardless of Joaquin's precise motion, any approach toward the U.S. East Coast would exacerbate what is becoming a serious flooding threat over a large area, due to a preexisting front being overtopped by near-record amounts of water vapor streaming over the region ahead of the trough that will help steer Joaquin (see Figure 7).


Figure 6. Rainfall observed over the 24-hour period ending at 1200 GMT (8:00 am EDT) Wednesday, September 30, 2015. Image credit: NOAA Advanced Hydrologic Prediction Service.


Figure 7. Moisture from several parts of the tropics was converging on the Northeast United States between 700 and 500 mb (roughly 2 to 4 miles high) at 1530Z (11:30 am EDT) Tuesday, September 29, 2015. The depiction of moisture channels on this image was created by Sheldon Kusselson atop a map of precipitable water (the amount of water vapor above particular points) produced using data from multiple sensors by the Cooperative Institute for Research in the Atmosphere. The water-vapor analysis system was recently highlighted in a paper in the Journal of Operational Meteorology. Image credit: Sheldon Kusselson and CIRA/CSU.


Flash flooding has popped up in several spots from Virginia to Maine over the last day (see the embedded tweet below from Belfast, ME). Portland, ME, received 5.61" of rain between midnight and 3:00 pm EDT Wednesday, overwhelming drainage systems and causing widespread street flooding. This morning's 7-day outlook from the NOAA Weather Prediction Center showed a vast area of 5-10" rainfall amounts from North Carolina to southern New England, and flood watches are posted for most of the U.S. East Coast. Model output suggests that localized 7-day totals of 10-20" or more are not out of the question, depending on Joaquin's exact track. The potential for major, widespread flooding-related impacts from Joaquin, in combination with the already-unfolding heavy rain event, should be taken very seriously.

We'll have our next update on Joaquin by Thursday morning at the latest.

Jeff Masters and Bob Henson




Bob Henson will be on WUTV on the Weather Channel at 6:20 pm EDT Wednesday, and Jeff Masters will be on at 7:20 pm.

Hurricane

Hurricane Warnings for the Bahamas From Joaquin; Threat to U.S. East Coast Grows

By: Jeff Masters and Bob Henson , 3:38 PM GMT on September 30, 2015

Joaquin is now a hurricane, and Hurricane Warnings are up for the Central Bahama Islands as the slowly intensifying storm moves southwest at 6 mph. An Air Force hurricane hunter aircraft made two penetrations of Joaquin's center on Wednesday morning, and found top surface winds of 80 mph, a central pressure of 971 mb, and a huge 54-mile diameter eye with a fully closed eyewall. Joaquin continues to battle high wind shear of 20 knots due to strong upper-level winds out of the north-northwest, but this wind shear had fallen by about 5 knots since Tuesday morning. Water vapor satellite loops show that a large area of dry air lay to the northwest of Joaquin, and the strong wind shear was driving this dry air into Joaquin's core, keeping intensification slow. Visible and infrared satellite loops show that Joaquin has developed a large Central Dense Overcast (CDO) of high cirrus clouds over the center, characteristic of intensifying storms, and the hurricane's large eye was beginning to be apparent. Upper level winds analyses from the University of Wisconsin show that the hurricane has developed an impressive upper-level outflow channel to the southeast, which is supporting the intensification process. Ocean temperatures in the region are near 30°C (86°F)--the warmest seen there since record keeping began in 1880.


Figure 1. MODIS image of Hurricane Joaquin approaching the Bahamas as seen from NASA's Aqua satellite on Wednesday, September 29, 2015, at approximately 12:30 pm EDT. At the time, Joaquin had top winds of 80 mph. Image credit: NASA.

The U.S. outlook for Joaquin
A hurricane watch could be required for portions of the U.S. East Coast as early as Thursday night. The forecast for Joaquin is very complex, and the confidence in both the intensity and track forecast for the storm is low. Joaquin is trapped to the south of a high pressure system whose clockwise flow will push the cyclone very slowly to the southwest or west-southwest at about 3 - 6 mph. As the storm progresses to the southwest, the strong upper-level winds out of the north currently bringing high wind shear of 20 knots will gradually decrease, continuing to allow Joaquin to strengthen. The 8 am EDT Wednesday run of the SHIPS model predicted that wind shear over Joaquin would fall to the moderate range, 10 - 20 knots, on Thursday and Friday. These conditions should allow Joaquin to intensify to a Category 2 hurricane by Thursday. As Joaquin progresses to the west, the storm will also increasingly "feel" the steering influence of a strong upper-level trough of low pressure situated over the Eastern United States on Friday, and begin to turn north. These winds may also open up another upper-level outflow channel to the northwest of Joaquin on Friday, potentially allowing the storm to intensify to Category 3 strength. However, as Joaquin gets closer to this trough, its winds will bring high wind shear of 20+ knots, likely halting the intensification process and causing weakening by Sunday.


Figure 2. Our two top models for forecasting hurricane tracks, both run at 8 pm EDT Tuesday September 29, 2015 (00Z Wednesday) , came up with two very different solutions for the path of Joaquin. The GFS model showed Joaquin making landfall in Virginia, while the European model took the storm to the northeast out to sea without hitting the U.S. Image credit: wundermap with the "Model Data" layer turned on.



Figure 3. The ensemble runs of our two top models for forecasting hurricane tracks, both run at 8 pm EDT Tuesday September 29, 2015 (00Z Wednesday). The 50 members of the European model ensemble (top) and the 20 members of the GFS model ensemble (bottom) both had numerous model runs that took Joaquin into U.S. East Coast, and ones that missed the U.S. coast entirely. Ensemble runs take the operational version of the model and run it at lower resolution with slightly different initial conditions, to generate an "ensemble" of possible forecasts. The operation high-resolution (and presumably best-guess) forecast for the models is shown in red. The European model ensemble had four members that tracked the movement of Joaquin exceptionally well during the previous 12 hours; three of those four members had tracks for Joaquin that missed the U.S., and one that hit the coast near New York City. Image taken from a custom software package used by TWC.

The big trend from the 00Z Wednesday (8 pm EDT Tuesday) suite of computer model guidance was a marked convergence toward a landfall in the vicinity of North Carolina or Virginia. The 00Z HWRF and GFDL models were joined by the 00Z GFS in hooking Joaquin toward the northwest on Friday and accelerating the hurricane into the coast between Cape Hatteras, NC, and the Delmarva Peninsula as a significant hurricane on Saturday/Sunday. The high-resolution HWRF and GFDL output showed central pressures in the 940-950 mb range at landfall, with wind speeds on par with a Category 2 hurricane. The 00Z UKMET solution angled more north-northwestward, with Joaquin arriving near the southern end of the Delmarva and scraping up the coast into eastern New Jersey and New York. Among the major dynamical models, only the European (ECMWF) model remained adamant that Joaquin would head to sea well before reaching the southeast U.S., although its 00Z track was a bit west of previous runs. The leftward hook prominently featured in the other models is being driven by the increasingly negative tilt (NW-to-SE) to the upper trough deepening over the eastern U.S. late this week. The models are projecting that this trough would pull in Joaquin on its northeast side, in much the same way that a strong upper-level low did with Hurricane/Superstorm Sandy in 2012. However, in Joaquin's case, the process would unfold a couple of hundred miles to the south. The ECMWF run shows a very similar upper-level pattern to the other models, but the timing of the trough's interaction with Joaquin and with Invest 90L is such that the hurricane is shunted to sea instead of being tucked into the northeast side of the trough. 90L was centered at 8 am EDT Wednesday about 1000 miles east-northeast of Joaquin. In their 8 am EDT Wednesday Tropical Weather Outlook, NHC gave 90L 2-day and 5-day odds of development of 40% and 70%, respectively.


Figure 4. Model track guidance initialized at 12Z Wednesday (8 am EDT) shows a continued clustering of model solutions toward North Carolina and the mid-Atlantic. This early-track guidance uses 12Z data on Joaquin to update the previous model runs from 06Z. This map does not include the ECMWF model, whose 00Z operational run took Joaquin out to sea. Image credit: Levi Cowan, tropicaltidbits.com.

Back in 2012, the ECMWF model caught on to the leftward hook of Sandy's track several days before other models. The ECMWF's high overall skill means we cannot entirely discount its out-to-sea forecast for Joaquin just yet. At the same time, the strong consistency among other leading models in projecting a NC/mid-Atlantic landfall cannot be ignored. We can gain more perspective on this scenario by looking at the ECMWF and GFS ensemble output from 00Z Wednesday. In each ensemble, the model is run a number of times for the same situation, but with the starting conditions varied slightly to represent the uncertainty in our starting-point observations of the atmosphere. The ECMWF and GFS ensembles from 00Z Wednesday are much more similar in flavor than you might expect from looking at their single operational runs. Both models have a majority of ensemble members heading for North Carolina and the mid-Atlantic, with a few outliers heading to sea.

If Wednesday's 12Z (8 am EDT) models continue to zero in on a NC/VA landfall, and especially if the ECMWF comes more fully around, then this solution will become a more high-confidence forecast. The NHC has been nudging its "cone of uncertainty" toward the left, still splitting the difference between the ECMWF and other solutions while acknowledging the westward trend. The entire U.S. coast from the Outer Banks of NC to southern New England was located in the 5-day cone issued at 11 am EDT Wednesday and valid at 2 am EDT Monday. Even if NHC moves more fully toward the NC/mid-Atlantic scenario, we can still expect to see a large swath of coastline remaining in the "cone" as we get closer to Joaquin's eventual landfall.

Potential impacts from Joaquin
Apart from the remaining uncertainty about a U.S. landfall, Joaquin is now poised to bring hurricane-force conditions into or very close to the southeastern Bahamas. WIth luck, these islands will remain on the weaker left-hand side of Joaquin. If the hurricane makes a sharp turn to the north on Friday as predicted, the effects should be considerably less on the northwestern Bahamas.

It is relatively rare for a hurricane to make a Sandy-like left hook into the U.S. East Coast. Such a track was unprecedented for New Jersey in hurricane annals, and even in the NC/VA area, it is uncommon enough that the likely effects would be both unusual and high-impact. The closest analogue from recent years is 2003's Hurricane Isabel. After a much longer life as a Cape Verde system and a Category 4 hurricane from the Central Atlantic (briefly a Category 5), Isabel angled sharply northwestward and made landfall on North Carolina's Outer Banks as a strong Category 2 hurricane. Isabel then continued on a fairly direct track to western Pennsylvania as it weakened. Isabel's trajectory brought huge surf to the coast from North Carolina to New Jersey, with a major storm surge pushing into the Chesapeake Bay and nearby waterways, plus widespread impacts from high wind and heavy rain. Joaquin is not as large or long-lived a storm as Isabel, but if it moved slightly to the north of Isabel's path, its track could be even more favorable for a Chesapeake surge. Hurricane-force winds would be another factor to contend with, especially just north of Joaquin's track during and just after landfall. Storm surge expert Dr. Hal Needham of LSU has a detailed look at the potential for storm surge from Joaquin along the U.S. East Coast in his Wednesday morning blog post, Widespread Storm Surge Event to Impact U.S. Atlantic Coast.

One very worrisome aspect of Joaquin is the torrential rains that it could bring from the Carolinas to the Northeast and perhaps even New England. Heavy rains and scattered flash flooding have already occurred in parts of these areas over the last 24 hours, as a preexisting front is overtopped by near-record amounts of water vapor streaming over the region ahead of the trough that will help steer Joaquin. The hurricane itself, arriving after several days of antecedent rainfall, has the potential to produce truly historic rainfall totals. This morning's 7-day outlook from the NOAA Weather Prediction Center, which goes with the NC/mid-Atlantic scenario, shows widespread 5-10" amounts from North Carolina to southern New England. Model output suggests that localized 7-day totals of 10-20" or more are not out of the question, depending on Joaquin's exact track. We'll have more on the ongoing and potential flood risk in our afternoon post.


Figure 5. Projected 7-day rainfall amounts from 12Z Wednesday, September 30, to 12Z October 7. Image credit: NOAA Weather Prediction Center.

We'll have a new post this afternoon.

Jeff Masters and Bob Henson

Hurricane

Joaquin Intensifying; Potential Threat for Bahamas and U.S. Coast

By: Bob Henson and Jeff Masters , 9:08 PM GMT on September 29, 2015

Tropical Storm Joaquin is gaining strength as it moves slowly west-southwest toward the eastern Bahamas. Joaquin’s top sustained winds were upgraded from 50 to 65 mph in the 5:00 pm EDT Tuesday advisory from the National Hurricane Center (NHC). An Air Force hurricane-hunter aircraft found a central pressure of 990 millibars, a substantial drop from this morning. From aboard the aircraft, NOAA’s Stepped Frequency Microwave Radiometer detected surface winds on the order of 60-65 mph (see Figure 2) at around 2:00 pm EDT. Joaquin has struggled in the face of wind shear of 20-25 knots due to strong upper-level winds from the north-northwest; earlier Tuesday, the the low-level center of circulation exposed to view with all of the storm's heavy thunderstorms limited to the southeast side of the center. However, the thunderstorms maintained their vigor with the help of very warm waters and excellent outflow toward the south side of Joaquin, and on Tuesday afternoon an intense burst of thunderstorms developed atop the low-level center. With this consolidation, Joaquin has a much better chance to intensify further in the next 24 hours. Wind shear will be dropping below 20 knots by Wednesday and may dip below 15 knots for several days, lending more support to intensification. NHC now projects that Joaquin will be a hurricane by midday Wednesday.


Figure 1. Infrared satellite image of Tropical Storm Joaquin, collected at 1945Z (3:45 pm EDT) on Tuesday, September 29, 2015. Image credit: NOAA/NESDIS.


Figure 2. MODIS image of Tropical Storm Joaquin near the Bahamas as seen from NASA's Aqua satellite on Tuesday, September 29, 2015, at approximately 10:30 am EDT. At the time, Joaquin had top winds of 45 mph. Image credit: NASA.


Figure 3. Surface winds (blue line) and precipitation (red line) as measured by the Stepped Frequency Microwave Radiometer (SFMR) instrument on an Air Force hurricane hunter aircraft on Tuesday, September 29, 2015, between 1:35 - 3:34 pm EDT. Surface winds peaked at about 57 knots (66 mph) at 2:13 pm, during a period when heavy rain was observed. Surface winds of 51 knots (59 mph) were observed during a period of low precipitation. Image credit: Levi Cowan, tropicaltidbits.com.


Over the next couple of days, models agree that Joaquin will continue moving slowly toward the west-southwest, which will pose an increasing threat to the eastern Bahamas. The NHC may issue watches or warnings for the Bahamas later Tuesday night. Most of the 12Z Tuesday computer models stop Joaquin in its tracks just short of the Bahamas, but the usually reliable ECMWF model suggests a greater motion toward the southwest, indicating a potential threat to some of the eastern islands. During its slow westward trek, Joaquin will be passing over ocean temperatures near 30°C (86°F)--the warmest seen there since record keeping began in 1880. Oceanic heat content--the amount of energy stored in the upper 50 meters (160 feet) of the ocean--is another index of potential strengthening. Joaquin’s track should take it across the boundary into oceanic heat content values greater than 50 kilojoules per square centimeter by Wednesday. For tropical storms and Category 1 hurricanes, values of heat content greater than 50 kJ/cm2 have been associated with more rapid intensification rates, assuming that wind shear is less than 15 knots, mid-level relative humidity is greater than 50 percent, and SSTs are at least 28.5°C. Joaquin should meet most or all of these criteria over the next couple of days, which raises the possibility of robust intensification.


Figure 4. On Tuesday, September 29, 2015, Tropical Storm Joaquin was located in an area of ocean with record Sea Surface Temperatures (SSTs) of 30°C (86°F). Image credit: NOAA/NCEI.


Figure 5. Oceanic heat content across the Northwest Atlantic as of September 28, 2015. Values of greater than 50 kJ/cm2 are related to more rapid intensification of tropical cyclones up to Category 1 strength, assuming that other conditions are supportive (warm SSTs, moist mid-level air, and light wind shear). Image credit: NOAA/AOML.


The long-range outlook for Joaquin
The 12Z Tuesday model runs did not clarify the unusually muddy waters surrounding the future track of Joaquin. By Friday, the eastern U.S. trough should begin to influence Joaquin and give it a northward component of motion, but the exact configuration of that trough--which will be critical to Joaquin’s track beyond Day 3--is still unclear. The models continue to show huge differences from run-to-run and with each other on just how this trough will develop and interact with Joaquin. The general tendency is for this trough to take on a negative tilt (a NW-to-SE configuration), with upper-level ridging becoming stronger off New England. All else being equal, this would tend to result in a more northwesterly path for Joaquin. Complicating the forecast is the presence of several areas of disturbed weather, including the remnants of Invest 99L (now over northern Florida); Invest 90L (incorporating the remnants of Tropical Storm Ida); and a frontal zone across the Northeast that will produce torrential rain (see below). All of these systems will pump large amounts of heat into the atmosphere through condensation, and this in turn will influence how the situation evolves.


Figure 6. Two model runs, just 12 hours apart, from one of our top models for predicting hurricane tracks--the European model--showed radically different solutions over 900 miles apart for where Joaquin might be in 5 - 5.5 days. The latest model run (8 am EDT Sept 29) reverted back to a solution close to the one shown above on the left. Image credit: wundermap with the "Model Data" layer turned on.


Figure 7. Ensemble members from the GFS model run at 12Z Tuesday, September 29, 2015, show a huge spread in where Joaquin might end up. The ensemble is produced by running the model multiple times, each time varying the starting-point conditions slightly to mimic observational uncertainty.

The model guidance from 12Z Tuesday shows two main possibilities by Days 5 and 6. The HWRF, GFDL, and UKMET models all depict a hurricane heading toward the mid-Atlantic by this weekend, tucking into the north side of the negatively tilted trough. In contrast, the ECMWF and GFS models show Joaquin heading out to the open Atlantic well before approaching the U.S. East Coast, as the trough pushes Joaquin eastward rather than pulling it into its northeast side. Various members of the ECMWF and GFS model ensembles have a wide range of solutions (see Figure 7 at right). Given the complexity of the factors involved, it is far too soon to put too much stock in any particular model solution. This is a good time to keep in mind that the width of the National Hurricane Center’s “cone of uncertainty” is based on average historical forecast errors from the last five years. In the case of Joaquin, the long-range uncertainty indicated by the models right now appears even larger than the cone’s historical database would suggest, which calls for even more caution than usual in focusing on any possible outcome. Data from the first dropsonde mission into Joaquin this afternoon by the NOAA Gulfstream-IV jet should make Tuesday night's 00Z suite of computer model forecasts more reliable than the Tuesday morning runs.

Regardless: heavy rain event coming to northern Appalachians and New England
Independent of Joaquin, an unusually intense heavy-rain event will be striking the northern Appalachians and New England over the next 2-3 days. Deep tropical moisture streaming northeastward from the Gulf of Mexico will lead to near-record high amounts of water vapor for the location and time of year. This moisture will intercept a preexisting frontal boundary, as rain-producing impulses move along the east side of the sprawling upper-level trough over the eastern U.S. The NOAA Storm Prediction Center is calling for widespread 3-5” rainfall from 00Z Wednesday to 00Z Friday from eastern New York across most of New England to southeastern Maine. Models are in fairly strong agreement that this heavy rain will develop, but there is some uncertainty on where the rains will be heaviest--in particular, the placement of the southwest-northeast stripe where training echoes could lead to particularly large amounts. Dry conditions have prevailed over the mid-Atlantic and New England over the last few weeks, moderate drought near the coast, so most locations could handle several inches of rain before general flooding became an issue. However, if intense rains fall in a short period over mountainous areas, some smaller creeks and streams could respond quickly and produce a localized flash flood threat. Urban areas from New York to Portland may also experience street flooding if the heaviest rains materialize there, as the drainage systems struggle to keep up. If Joaquin happens to move into New England early next week, there would be a much greater risk of widespread flooding.

Which track model should you trust?
According to the 2014 National Hurricane Center Forecast Verification Report, issued in March 2015, in 2014 we had two track models that at times out-performed the official NHC forecast, a feat that is tough to do. NOAA's HWRF model did slightly better than the NHC official forecast for 2-day and 3-day forecasts, while the UK Met Office's forecast did slightly better than NHC's 4-day and 5-day forecasts. Once again, the European Center (ECMWF) and GFS models excellent performers, but the GFDL model, a excellent performer in recent years, had substantially poorer forecasts than the other four models. The Canadian CMC model and simple BAMM model had accuracies comparable to the GFDL model. The European Center model and GFS models were virtually tied as the best performing models when averaged over the three-year period 2012 - 2014.

Wunderground has a web page with computer model forecasts for Joaquin for many of the best-performing track models used to predict hurricane tracks. The European Center does not permit public display of tropical storm positions from their hurricane tracking module of their model, so we are unable to put ECMWF forecasts on this page (you can use our wundermap with the "Model Data" layer to look at ECMWF forecasts, though.) Here are some of the better models NHC regularly looks at:

ECMWF: The European Center's global forecast model
GFS: NOAA's global forecast model
UKMET: The United Kingdom Met Office's global forecast model (not evaluated by NHC in 2013)
GFDL: The Geophysical Fluid Dynamics Laboratory's hurricane model, initialized using GFS data
HWRF: The intended successor for the the GFDL hurricane model, also initialized using GFS data
NAVGEM: The Navy's global forecast model (which replaced the defunct NOGAPS model in 2013)
CMC: The Canadian GEM model
BAMM: The very old Beta and Advection Model (Medium layer), which is still useful at longer ranges

If one averages together the track forecasts from the first five of these models, the NHC official forecast will rarely depart much from it. These are the five models used to formulate the TVCA consensus model seen in Figure 8; the TVCA model was very close to the official NHC forecast in 2014.


Figure 8. Skill of computer model forecasts of Atlantic named storms in 2014, compared to a "no skill" model called "CLIPER5" that uses just climatology and persistence to make a hurricane track forecast (persistence means that a storm will tend to keep going in the direction it's current going.) OFCL=Official NHC forecast; GFS=Global Forecast System model; GFDL=Geophysical Fluid Dynamic Laboratory model; HWRF=Hurricane Weather Research Forecasting model; ECMWF=European Center for Medium Range Weather Forecasting model; UKMET=United Kingdom Met Office model; TVCA=one of the consensus models that blends together up to five of the above models; CMC=Canadian Meteorological Center (GEM) model; BAMM=Beta Advection Model (Medium depth). Data taken from the National Hurricane Center 2014 verification report.


Figure 9. Radar image of Tropical Storm Marty taken at 2:41 pm EDT from the Acapulco radar.

Tropical Storm Marty bringing heavy rains to Mexico's Pacific coast
After a 12-hour stint overnight as a Category 1 hurricane, Tropical Storm Marty weakened to a tropical storm with top winds of 60 mph at 11 am EDT Tuesday. Radar images out of Acapulco show that Marty continues to bring heavy rain showers to the coast, and as of 8 am EDT Tuesday, the heaviest 24-hour rains along the coast were in the 3 - 3.5" range. With high wind shear of 30 knots now affecting Marty, continued weakening is likely. Marty may have made its closest approach to the coast, as steering currents are now lining up to drive Marty to the west, away from the coast, beginning on Wednesday morning. Given that Marty is a small storm that is weakening and likely to begin moving away from the coast soon, Mexico should be able to avoid widespread destructive flooding from the storm.

Bob Henson and Jeff Masters

Hurricane

Tropical Storm Joaquin a Potential Threat to the Bahamas and U.S. East Coast

By: Jeff Masters and Bob Henson , 3:02 PM GMT on September 29, 2015

Tropical Storm Joaquin formed on Monday evening in the waters between Bermuda and the Bahamas, and could be a threat to both the Bahamas and the U.S. East Coast late this week. Joaquin was struggling some on Tuesday morning, due to high wind shear of 20 - 25 knots from strong upper-level winds out of the north-northwest. Water vapor satellite loops show that a large area of dry air lay to the northwest of Joaquin, and the strong wind shear was driving this dry air into Joaquin's core, keeping the low-level center of circulation exposed to view with all of the storm's heavy thunderstorms limited to the southeast side of the center, as seen on visible satellite loops. However, the thunderstorms maintained their vigor with the help of record warm waters and excellent outflow toward the south side of Joaquin, allowing the storm to intensify to 50 mph winds by 11 am EDT Tuesday. Ocean temperatures in the region are near 30°C (86°F)--the warmest seen there since record keeping began in 1880. The Hurricane Hunters will fly into Joaquin on Tuesday afternoon, and the first dropsonde mission from the NOAA jet is scheduled for Tuesday afternoon, as well.


Figure 1. Latest satellite image of Joaquin.

Forecast for Joaquin
The forecast for Joaquin is very complex, and the confidence in both the intensity and track forecast for the storm is very low. Joaquin is trapped to the south of a high pressure system whose clockwise flow will push the cyclone very slowly to the west or west-southwest at about 4 - 5 mph. As the storm gets farther from the high, the strong upper-level winds out of the north currently bringing high wind shear of 20 - 25 knots will gradually decrease, allowing Joaquin to strengthen. The 8 am EDT Tuesday run of the SHIPS model predicted that wind shear over Joaquin would fall to the moderate range, 10 - 20 knots, by Tuesday evening, then to the low range, 5 - 10 knots, Wednesday through Thursday. It would not be a surprise if Joaquin was a Category 1 hurricane by Thursday. As Joaquin progresses to the west, the storm will also increasingly "feel" the steering influence of a strong trough of low pressure situated over the Eastern United States. This trough features a flow of winds from southwest to northeast, which will tend to push Joaquin more to the north or northeast, roughly parallel to the U.S. coast or out to sea towards Bermuda. However, the models are showing huge differences from run-to-run and with each other on just how this trough will develop and interact with Joaquin. The Tuesday morning (00Z and 06Z) runs of the GFS model showed the trough absorbing Joaquin and destroying the storm by this weekend. The 00Z Tuesday run of the European model showed Joaquin getting slung northeastwards out to sea, well away from the U.S. coast. The 00Z Tuesday run of the UKMET model had Joaquin interacting with the trough in such a way that the trough would tilt westwards, leading to the unusual situation that we saw with Hurricane Sandy of 2012, where the storm would head towards the coast on a northwesterly track (this was also the solution the European model had in its run 12 hours previously.) The 06Z Tuesday runs of the GFDL and HWRF models had Joaquin heading northeast out to sea, then rotating back to the northwest this weekend to potentially threaten the Northeast U.S. as a strong tropical storm. The models are so different, in part, due to the uncertainty with how long Joaquin's current slow motion will last. Another wildcard how the moisture from tropical disturbance 99L, which pushed ashore into the Florida Panhandle Tuesday morning, will affect the trough of low pressure that will be steering Joaquin later this week. The long-range forecast is complicated by the possible interaction with the remains of Tropical Storm Ida (now designated as Invest 90L), centered at 11 am EDT Tuesday about 1000 miles east of Joaquin. their 8 am EDT Tuesday Tropical Weather Outlook, NHC gave 90L 2-day and 5-day odds of development of 10% and 40%, respectively. Data from the NOAA jet from today should make Tuesday night's 00Z suite of computer model forecasts more reliable than the Tuesday morning runs, though.


Figure 2. Two model runs, just 12 hours apart, from one of our top models for predicting hurricane tracks--the European model--showed radically different solutions over 900 miles apart for where Joaquin might be in 5 - 5.5 days. Image credit: wundermap with the "Model Data" layer turned on.

Regardless: heavy rain event coming to northern Appalachians and New England
Adding to the complexity and hazard of this situation, an unusually intense heavy-rain event will be striking the northern Appalachians and New England over the next 2-3 days. These rains would greatly enhance the potential for Joaquin to cause flooding afterward if it happened to move nearby. Over the next couple of days, deep tropical moisture streaming northeastward from the Gulf of Mexico will lead to extremely high amounts of water vapor for the location and time of year. This moisture will intercept a preexisting frontal boundary, as rain-producing impulses move along the east side of the sprawling upper-level trough over the eastern U.S. The NOAA Storm Prediction Center is calling for a band of widespread 3-5” rainfall from central Pennsylvania to southern Maine. Models are in fairly strong agreement that this heavy rain will develop, but there is some uncertainty on where the rains will be heaviest--in particular, the placement of the southwest-northeast stripe where training echoes could lead to particularly large amounts. The 0600 GMT (2:00 am EDT) Tuesday runs of the NAM and GFS models indicate a large swath of 4-5” rainfall, with many embedded areas of 5-10” potential, through 2:00 am EDT Friday, extending from Pennsylvania and New York across northern and central New England. Dry conditions have prevailed over the mid-Atlantic and New England over the last few weeks, with moderate drought near the coast, so most locations could handle several inches of rain before flash flooding became an issue. Any direct impacts from Joaquin would only add to the eventual flood risk.

 
Figure 3. Projected 3-day rainfall totals from 1200 GMT (8:00 am EDT) Tuesday, September 29, 2015, through 1200 GMT Friday, October 2. Isolated local amounts could be considerably higher. 

 
Figure 4. Short-Range Ensemble Forecast (SREF) plumes, produced at 0300 GMT (11:00 pm EDT) Tuesday, September 29, 2015, showing potential rainfall in Boston through 1800 GMT (2:00 pm EDT) Friday, October 2. Each trace corresponds to a particular model run. The ensemble average indicates that around 3" - 4" could be expected, though larger amounts are possible. The ensemble consists of three model "families" (WRF-ARW, WRF-NMM, and NAM), each run with varying initial conditions to represent uncertainty in the atmosphere's starting point. Image credit: NOAA Storm Prediction Center.

We'll have a full update on the Joaquin this afternoon by 4 pm EDT, when the latest 12Z (8 am EDT) suite of model runs will be available. We'll also have an update on the action in the remainder of the tropics.

Jeff Masters and Bob Henson

Hurricane

Dujuan Slams into Taiwan; TD 11 Forms in Northwest Atlantic

By: Bob Henson and Jeff Masters , 5:05 PM GMT on September 28, 2015

The center of Typhoon Dujuan slammed into the northeast coast of Taiwan near the rural township of Nan’ao at 5:40 pm Monday local time (5:41 am EDT Monday). Dujuan’s highest 1-minute sustained winds were 140 mph at the final advisory (0600 GMT or 2 pm local time Monday) from the Joint Typhoon Warning Center (JTWC) prior to its landfall. Using a different interval for top sustained winds, the Hong Kong Observatory classified Dujuan as a super typhoon. Dujuan was a spectacularly well-structured annular storm as it approached Taiwan, and satellite loops showed little sign of weakening prior to landfall, so Dujuan likely came onshore as a Category 4 typhoon. En route to Taiwan, Dujuan produced a record 181-mph (81.1 m/s) wind gust at the southern Japanese island of Yonagunijima, according to weather.com and the Japan Meteorological Agency.


Figure 1. A stunning true-color view of Typhoon Dujuan from Japan’s Himiwari-8 satellite at sunrise on Sunday, September 27, about 24 hours before the typhoon struck Taiwan. Image credit: JMA, courtesy Dan Lindsey.


Figure 2. A close-up visible image of Typhoon Dujuan at 500-meter resolution, again from Japan’s Himiwari-8 satellite near sunrise on Sunday, September 27. Image credit: JMA, courtesy Dan Lindsey.


Figure 3. An enhanced infrared image from the MTSAT satellite of Typhoon Dujuan at 0801 GMT Monday, September 28, less than two hours before Dujuan made landfall on Taiwan’s northeast coast. Image credit: NOAA/NESDIS.

The powerful right-hand eyewall of Dujuan passed near the urbanized area of Yilan County as Dujuan made landfall. A wind gust of 153 mph (68.4 meters per second) was reported at Su’ao Township, about 20 miles south of Yilan City. At 1500 GMT (11 pm local time or 11:00 am EDT Monday), Taiwan’s Central Weather Bureau (CWB) placed Dujuan at 24.0°N and 120.6°E, or about 70 miles south-southwest of Taipei, which was experiencing the northern edge of the eyewall’s heavy rain. The typhoon angled further toward the west-southwest than expected during its trek over Taiwan, helping to spare Taipei from the worst potential impacts. At 1200 GMT Monday, the JTWC reported that Dujuan’s top sustained 1-minute winds were down to 115 mph. The CWB reported at 1500 GMT that the minimal central pressure at 1500 GMT had risen to 945 millibars, from 925 millibars at 1200 GMT.


Figure 4. A woman uses an umbrella against strong wind and rain brought by Typhoon Dujuan at Tamshui district, New Taipei City on September 28, 2015. More than 7,000 people were evacuated in Taiwan as Dujuan swirled towards the island, gathering strength as it bore down on the east coast. Heavy rain and wind struck the Taipei area well ahead of Dujuan’s core. Image credit: Sam Yeh/AFP/Getty Images.


Figure 5. Radar imagery at 11:18 pm local time (11:18 am EDT) Monday, September 28, showed heavy rains from Typhoon Dujuan still enveloping most of Taiwan, with outer bands stretching to the coast of China. Image credit: Central Weather Bureau, Taiwan.

Torrential rains have been falling over most of Taiwan, with particularly heavy amounts likely over east-facing northern slopes and west-facing southern slopes. Totals as high as 30 inches have already been reported. By Tuesday morning, Dujuan should be making landfall on China’s east coast as a rapidly decaying Category 1 typhoon.

Heavy rains can still be expected as Dujuan recurves into the Yangtze River valley from Tuesday into Wednesday, and these could inflict a major disaster in their own right. Dujuan is a bit stronger than Typhoon Soudelor, which struck Taiwan on August 7, but Soudelor’s track across Taiwan and into China is quite similar to the projections for Dujuan. Soudelor caused at least 26 deaths in China compared to at least 8 in Taiwan, and estimated losses in China of at least $3 billion were much greater than the reported $95 million US in agricultural damage in Taiwan. The Joint Typhoon Warning Center projects Dujuan to strike the China coast within 30 miles of Soudelor’s landfall point near Putian City.

TD 11 worth watching in Northwest Atlantic
Tropical Depression 11 took shape last night in the Northwest Atlantic between the Bahamas and Bermuda. In the grip of moderate to strong northwesterly wind shear (around 20 knots), TD 11 is struggling to organize itself, with an exposed low-level center on Monday morning. Showers and thunderstorms are fairly widespread and have persisted into Monday morning, beyond the typical nighttime convective maximum. The depression is over very warm sea-surface temperatures of around 30°C (86°F), about 1°C above average. As TD 11 moves slowly northwest over the next 2-3 days, it will remain over quite warm SSTs, but wind shear will remain on the strong side, denting TD 11’s potential for growth. Dynamical models are in general agreement in bringing TD 11 to tropical storm strength over the next several days. The high-resolution HWRF model is particularly bullish, with its 00Z and 06Z runs bringing TD 11 to hurricane status by later this week.


Figure 6. Latest satellite image of Tropical Depression 11.


Figure 7. The five-day forecast for TD 11 from the National Hurricane Center.

Upper-level steering currents forecast for later this week feature strong southerly flow between an eastern U.S. trough and a western Atlantic ridge, which suggests TD 11 (or its remnants) should be heading in the general direction of southern New England toward the end of this week. The high-resolution HWRF and GFDL models lean the most strongly toward a potential landfall threat for Long Island by around Friday, while the global-scale ECMWF and GFS tend to keep TD 11 further to the east and considerably weaker. The official NHC outlook intensifies TD 11 only to minimal tropical storm status and transitions it to post-tropical status by Friday morning as it approaches New England, where it should be merging with a frontal zone. The best global models are typically more reliable than the high-resolution mesoscale models beyond about 2-3 days, but the newly upgraded HWRF has demonstrated impressive skill on several storms this year. TD 11 bears watching, as there seems at least a modest possibility of the system approaching the northeast U.S. coast as a subtropical or tropical storm.



Figure 8. Radar-estimated rainfall from 99L from the Pensacola, Florida radar ending at noon EDT Monday showed several areas of 6+ inches of rain had fallen.

99L in Gulf of Mexico bringing heavy rain to the Gulf Coast
A Flash Flood Warning is posted for the Florida Panhandle near Pensacola and Flood Watches are up for the coast from Southeast Louisiana to Sarasota, Florida as an area of low pressure (Invest 99L) centered at 11 am EDT Monday over the south-central Gulf of Mexico, about 300 miles west-northwest of Key West, moves north-northeastwards at about 10 mph. A channel of low-level moisture running from 99L toward an upper-level low in Texas combined with upper-level moisture filtering in from Tropical Storm Marty (see below) to bring torrential rains of 7.50" to Mobile, Alabama on Sunday, making it their 10th wettest calendar day on record. This is the first time since records began in 1871 that the city has seen two 7+ inch rainfall days in one year; the city had 7.28" of rain on April 12. 99L is producing a large area of disorganized showers and thunderstorms that extends from western Cuba northward across the eastern Gulf of Mexico, but no well-defined surface circulation exists, as seen on satellite loops. A separate non-tropical low pressure system associated with the upper low can be seen over the northwestern Gulf of Mexico, and is bringing a few heavy rain showers to the Texas and Western Louisiana coast. By Tuesday morning, the center of 99L will push inland over the Florida Panhandle. High wind shear of 20 - 30 knots should limit the potential for 99L to organize into a named storm, and our top three models for predicting tropical cyclone genesis are showing little development of this system. 99L will likely bring heavy rains of 2 - 3" from Southeastern Louisiana to the Florida Panhandle. In their 8 am EDT Monday Tropical Weather Outlook, NHC gave the disturbance 2-day and 5-day odds of development of 30%. The Hurricane Hunters were in the air on Monday afternoon to investigate 99L.


Figure 9. MODIS image of Tropical Storm Marty approaching Mexico as seen from NASA's Terra satellite on Sunday, September 27, 2015, at 3:30 pm EDT. At the time, Marty had top winds of 60 mph. Image credit: NASA.

Tropical Storm Marty a dangerous heavy rain threat for Mexico's Pacific coast
Tropical Storm Marty has intensified to just below hurricane strength, with top winds of 70 mph at 11 am EDT Monday, as the storm drifts northwards at 3 mph towards the Pacific coast of Mexico to the northwest of Acapulco. With Marty stuck in a region of weak steering currents and likely to remain just offshore through Wednesday, the storm is a dangerous storm for the Pacific coast of Mexico. Heavy rains of 6 - 12" are likely to cause dangerous flooding and mudslides today through Wednesday. As of 8 am EDT Sunday, Petacalco on the coast received 3.62" of rain in 24 hours, though rainfall amounts for the 24-hour period ending on Monday morning were generally less than one inch along the Mexican coast. Further intensification of the storm appears unlikely, due to high wind shear of 15 - 25 knots, close proximity to the coast, and the potential for Marty to upwell cool water from the depths that will diminish the storm's energy supply. An Air Force hurricane hunter aircraft will investigate Marty on Monday afternoon. The models are split on whether or not Marty will eventually make landfall this week, and the 3 to 5-day official forecast from NHC should be considered low-confidence.


Figure 10. MODIS image of Tropical Storm Niala skirting the Big Island of Hawaii as seen from NASA's Terra satellite on Sunday, September 27, 2015, at approximately 4 pm EDT. At the time, Niala had top winds of 50 mph, but its low-level center had become exposed to view due to high wind shear. Image credit: NASA.

Tropical Storm Niala spares Hawaii
Tropical Storm Niala passed about 150 miles south of the Big Island on Sunday, bringing a few heavy rain showers to the island, but not enough to cause flooding. The Flash Flood Watch for the island has been cancelled, but a High Surf Advisory remains in effect on Monday for waves of 5 to 8 feet along east and southeast facing shores of The Big Island. At 11 am EDT Monday, Niala had weakened to a tropical depression, and was moving west-southwest at 10 mph away from Hawaii. Niala should continue to weaken in the face of high wind shear, becoming a remnant low by Monday night.

Bob Henson and Jeff Masters

Hurricane

Category 4 Dujuan Takes Aim on Taiwan

By: Bob Henson and Jeff Masters , 5:41 PM GMT on September 27, 2015

Taiwan is bracing for the arrival of Typhoon Dujuan, which will tear across the northern part of the island on Monday night local time. Dujuan intensified rapidly over the weekend, growing from Category 1 to Category 4 strength in just 36 hours. As of 1200 GMT (8 am EDT) Sunday, Dujuan was packing winds of 145 mph, just short of supertyphoon levels. Dujuan has an annular structure, with a huge eye--more than 50 miles in diameter--and cyclonic banding limited to its south side. Sea-surface temperatures will continue above average and wind shear will remain very light (below 10 knots) along the remainder of Dujuan’s approach to Taiwan. Annular hurricanes are often relatively slow to weaken, which lends further support to the idea of Dujuan maintaining most or all of its current strength before it reaches Taiwan. The path projected by the Joint Typhoon Warning Center on Sunday morning has Dujuan onshore as a Category 3 typhoon at 1200 GMT (8 pm Taiwan time) on Monday night, with Taipei on the dangerous right-hand side of the typhoon.


Figure 1. Infrared image from NASA’s VIIRS instrument of Typhoon Dujuan, taken at 0510Z (1:10 am EDT) on Sunday, September 27, 2015. Image credit: NOAA/NASA RAMMB/CIRA, courtesy Dan Lindsey.


Figure 2. MODIS image of Typhoon Dujuan approaching Taiwan as seen from NASA's Terra satellite on Sunday, September 27, 2015. Image credit: NASA.

Taiwan is vulnerable to large damages from typhoons
Taiwan and its capital city of Taipei are very vulnerable to large damages from typhoons. A September 2015 "City Risk Index" developed by Lloyds of London rated Taipei the most financially exposed city in the world to disasters, due to the wealth of the city and its exposure to disasters such as typhoons, earthquakes, floods, and volcanoes. The top risk factor: typhoons, which can potentially put $81 billion in assets at risk in the city. Taiwan has already been hit by one major typhoon this year--Typhoon Soudelor, which hit Taiwan as a Category 3 storm with 120 mph winds on August 8, killing 8 people and doing over $30 million in damage. More than 4 million power customers lost power in Taiwan; according to taipower.com, this is Taiwan's largest power outage ever caused by a typhoon. Torrential rain also impacted northern Taiwan; Datong Township, Yilan County, reported 52.52 inches of rain from Soudelor. Taiwan's most damaging typhoon was Super Typhoon Herb of July 1996. Herb hit the island as a Category 4 storm with 150 mph winds, passed directly over the capital of Taipei, and did $1.1 billion in damage.


Figure 3. A basketball court is flooded by the Jingmei River as Typhoon Soudelor hits Taipei, Taiwan on Aug. 8, 2015. (Sam Yeh/AFP/Getty Images)

Rains from Tropical Storm Niala to douse Hawaii
East- and south-facing slopes of Hawaii’s Big Island may get widespread rainfall of 2” – 8” and localized totals of 12” or more today through Monday as Tropical Storm Niala moves south of the state. As of 11 am EDT Monday, the exposed low-level center of Niala was located about 245 miles south-southeast of Hilo, moving west-southwest as 7 mph. The Tropical Storm Watch formerly in effect for Hawaii has been discontinued. Tropical storm force winds only extent up to 80 miles from the center, so high winds will not be a threat, but the lighter winds and rich moisture assocaited with Niala’s broader circulation will enhance the normal trade-wind flow that makes the east slopes of Hawaii’s volcanic peaks among the wettest places on the planet. The Big Island remains in a flash flood watch through Monday, with already-saturated ground increasing the risk of flash flooding. Niala’s top winds are just 50 mph, and southwesterly wind shear of more than 30 knots should weaken the storm to depression strength by late Monday or Tuesday as it angles to the southwest of Hawaii.


Figure 4. MODIS image of Tropical Storm Niala approaching Hawaii as seen from NASA's Aqua satellite on Saturday, September 26, 2015, at approximately 4 pm EDT. At the time, Niala had top winds of 65 mph, but its low-level center had become exposed to view due to high wind shear. Image credit: NASA.

Widespread rains in store for Gulf Coast
A broad area of surface low pressure sprawled across the western Gulf of Mexico, dubbed Invest 99L, will bring several days of scattered heavy rain from southeast Texas to much of Florida. The entire system is being steered by a nearly stationary upper low now centered along the Texas coast. The small low-level center of circulation of 99L is just north of the Yucatan peninsula, with another area of surface low pressure and concentrated showers and thunderstorms close to the Louisiana coast associated with the upper low. Southwesterly wind shear from the upper low should inhibit the multiple surface centers from consolidating into a tropical storm. However, a subtropical-type system may emerge, with numerous bands and clusters of convection sweeping into the Southeast from the Gulf Coast through Tuesday. An Air Force reconnaissance plane is on standby for a possible mission into 99L later Sunday, and NHC gives the system a 30% chance of tropical or subtropical development. The NOAA Weather Prediction Center is projecting widespread 2” – 3” totals along the immediate coast from Houston to Tampa, with lighter amounts further inland (see Figure 5). We can expect similar drenching set-ups to occur periodically through the fall and into the winter, as the powerful El Niño now in place will support a strong subtropical jet stream into the Gulf of Mexico and nearby states. The risk of tornadoes and other severe weather will increase during the winter months over Florida, where El Niño significantly boosts the odds of wintertime tornadoes.


Figure 5. Forecast rainfall amounts from 1200 GMT (8:00 am EDT) Sunday, September 27, through Wednesday, September 30. Image credit: NOAA/NWS Weather Prediction Center.

Tropical Storm Marty pondering a Mexican landfall
The future of Tropical Storm Marty is shrouded in an unusually high amount of uncertainty. Marty’s sustained winds had risen to 60 mph at 11 am EDT Sunday, with the center about 235 miles southwest of Acapulco. Very warm sea-surface temperatures of 30-31°C (86-88°F) are helping keep Marty’s convection robust despite moderate southwesterly wind shear (about 20 knots) as the storm inches northward at just 7 mph. The operational GFS model and most of the GFS ensemble members continue to bring Marty north and northeastward into the Mexican coast not far from Acapulco, while several ensemble members shunt Marty to the northwest, avoiding landfall. The ECMWF and UKMET models also take a weaker Marty northwestward and keep it offshore. None of the major models intensify Marty beyond minimal hurricane strength. Given the track uncertainty, NHC may issue a Tropical Storm Watch for the Mexican coast later on Sunday. NASA’s WB-57 aircraft is scheduled to release more than 50 dropsondes in and near Marty on Sunday as part of a research mission.


Figure 6. Latest satellite image of Tropical Storm Marty.

Ida clinging to life
Pesky Tropical Depression Ida continues to hang on as an identifiable cyclone in the central Atlantic--but just barely, with little organized convection. Ida is now on the south side of a upper-level ridge that should keep It rolling westward. Dynamical models all keep TD Ida below tropical storm strength throughout the next five days, and interactions with a front to its north may cause Ida to degenerate into a trough or remnant low at any time during the week.


Figure 7. Latest satellite image of Invest 98L.

Invest 98L could become a depression
West of Ida and east of the Bahamas, a gradually organizing area of showers and thunderstorms could become a tropical depression within the next couple of days. The system is passing over record warm ocean temperatures near 30°C (86°F), with wind shear in the moderate range (10 - 20 knots). NHC gives the system a 50% chance of development in the next three days. Wind shear is predicted to rise to the high range, 20 - 30 knots, beginning on Sunday night, which will likely put a cap on 98L’s development.


Figure 8. The total lunar eclipse of October 8, 2014, as photographed in California by Alfredo Garcia, Jr. Image credit: Wikimedia Commons/Tomruen.


It’s super-lunar-eclipse time tonight!
What could be the most spectacular lunar eclipse in decades will unfold tonight, as a “supermoon” coincides with a total lunar eclipse. The last time this happened was in 1982, and it won’t happen again until 2033. Sunday’s lunar eclipse is timed especially well for the Americas, with totality falling between around 7:00 to 8:30 pm PDT and 10:00 to 11:30 pm EDT. Evening skies should be fair or clear over much of the nation outside of the Southeast and the Atlantic coast. For more details, see the conclusion of our post from last Friday. If you can't see the eclipse directly, check out NASA's live feed from the Griffith Observatory in Los Angeles. Happy viewing!

Bob Henson and Jeff Masters


Hurricane

Tropical Storm Niala Approaching Hawaii; Heavy Rains for Gulf Coast Likely From 99L

By: Jeff Masters , 3:22 PM GMT on September 26, 2015

A Tropical Storm Watch and a Flash Flood Watch are posted for Hawaii's Big Island, as Tropical Storm Niala moves northwest at 8 mph on a course that will take it about 100 miles south of the Big Island on Sunday evening. With tropical storm-force winds expected to extend out up to 80 miles from the center at that time, the Central Pacific Hurricane Center in their 11 am EDT Saturday Wind Probability Forecast gave a 26% chance for South Point on the Big Island to receive tropical storm-force winds of 39+ mph. The bigger threat from the storm will be heavy rain, which could bring 6 - 12" of rain and dangerous flash floods to the Big Island on Saturday and Sunday.


Figure 1. Latest image from the South Hawaii radar.


Figure 2. Latest satellite image of Niala.

Niala is the record 7th named storm to form in 2015 in the North Central Pacific (between 140°W and the Date Line.) According to wunderblogger Dr. Phil Klotzbach, prior to 2015, the previous record for named storms in the North Central Pacific for an entire season was four, set in 1982. The other named storms that formed in the North Central Pacific in 2015 were Malia, Halola, Ela, Iune, Kilo and Loke. This year's record activity has been due to unusually low wind shear and record-warm ocean temperatures caused by the strong El Niño event underway.

99L in Gulf of Mexico to bring heavy rain to the Gulf Coast
A trough of low pressure is moving northwestwards across Mexico's Yucatan Peninsula, and is producing a large area of disorganized showers and thunderstorms over the northwestern Caribbean Sea and portions of Central America, as seen on satellite loops. On Saturday morning, NHC designated this area of interest Invest 99L. By Sunday, this activity will push into the Gulf of Mexico, where development into a tropical or subtropical depression could occur. However, an upper-level trough of low pressure over the Western Gulf of Mexico will bring high wind shear to the Gulf, limiting the potential for 99L to strengthen, and our top three models for predicting tropical cyclone genesis are showing little development of this system. The system will get pulled northwards to affect the U.S. coast from Louisiana to the Florida Panhandle Sunday afternoon through Tuesday, bringing heavy rains of 2 - 4". In their 8 am EDT Saturday Tropical Weather Outlook, NHC gave the disturbance 2-day and 5-day odds of development of 10% and 20%, respectively.

98L between Bermuda and the Bahamas of little concern
A non-tropical trough of low pressure (Invest 98L) is producing disorganized showers and a few thunderstorms over the western Atlantic Ocean several hundred miles south-southwest of Bermuda as the system drifts north to north-northwest at about 5 mph. With record warm ocean temperatures near 30°C (86°F) and wind shear in the moderate range, 10 - 20 knots, this disturbance may show some slow development on Saturday and Sunday. However, wind shear is predicted to rise to the high range, 20 - 30 knots, beginning on Sunday night. In their 8 am EDT Saturday Tropical Weather Outlook, NHC gave the disturbance 2-day and 5-day odds of development of 10% and 10%, respectively.

Little change to Ida
There is not much new to say about Tropical Depression Ida, which is wandering slowly over the Central Atlantic, well away from any land areas. Satellite images on Saturday morning showed Ida's center of circulation was fully exposed to view by high wind shear, and all of Ida's heavy thunderstorms were limited to the east side of the center. Ida will continue to move slowly in a region of weak steering currents for the next five days, and it is possible that high wind shear will destroy the storm by Tuesday, as suggested by Saturday morning runs of the GFS model.


Figure 3. MODIS image of Typhoon Dujuan as seen from NASA's Terra satellite on Saturday, September 26. Image credit: NASA.

Typhoon Dujuan bears down on Japan's Ryukyu Islands
Typhoon Dujuan, a Category 2 storm with 110 mph winds located about 325 miles south-southeast of Okinawa in Japan's Ryukyu Islands at 8 am EDT Saturday, is steadily intensifying as it heads northwest at 10 mph towards Taiwan. Wind shear is in the moderate range, 10 - 15 knots, and ocean temperatures are a very warm 29°C (84°F), conditions which favor intensification. Satellite loops on Saturday morning showed a large, well-organized storm with a huge 44-mile wide eye. Dujuan has taken on an annular appearance, with a large eye, thick eyewall, and very few low-level spiral bands. These type of storms are more resistant to weakening than ordinary, making Dujuan likely to maintain major typhoon status as it approaches Taiwan. The Joint Typhoon Warning Center (JTWC) projects that Dujuan will intensify to Category 4 strength by Sunday, and the storm is expected to pass near Taketomi-cho and Yonaguni-cho in Japan's Ryukyu Islands near 03 UTC Monday. The models have come into better agreement on the eventual fate of Dujuan, with a direct hit or very close pass by northern Taiwan looking increasingly likely.


Figure 4. Latest satellite image of Invest 93E (left side of image) and 92E (right side of image, close to the coast of Mexico/Central America.)

Tropical disturbances 92E and 93E a heavy rain threat to Mexico and Central America
Our three top models for predicting tropical cyclone genesis predict that an area of disturbed weather about 400 miles south of Acapulco, Mexico (Invest 93E) will develop into a tropical depression on Sunday or Monday. This system is expected to move northwards and be very near the coast close to Acapulco on Monday through Thursday, potentially bringing an extended period of dangerous flooding rains. In their 8 am EDT Saturday Tropical Weather Outlook, NHC gave the disturbance 2-day and 5-day odds of development of 90%.

Another area of disturbed weather in the Eastern Pacific along the coast near the Mexico/Guatemala border (Invest 92E) is drifting slowly to the west, and will bring heavy rains to El Salvador, southern Guatemala, and southeastern Mexico over the next few days. None of our reliable models for forecasting tropical cyclone genesis develop 92E into a tropical depression. In their 8 am EDT Saturday Tropical Weather Outlook, NHC gave the disturbance 2-day and 5-day odds of development of 30%.

Yet another area of concern is an area of low pressure that the models predict will form on Monday or Tuesday about 1000 miles southwest of the southern tip of the Baja California peninsula. Some gradual development of this system is possible later in the week while the system moves slowly northward. In their 8 am EDT Saturday Tropical Weather Outlook, NHC gave the disturbance 2-day and 5-day odds of development of 0% and 20%, respectively.

Jeff Masters

Hurricane

Heavy Rains Ahead for Gulf and Mid-Atlantic; Niala, Dujuan Prowl the Pacific

By: Jeff Masters and Bob Henson , 4:17 PM GMT on September 25, 2015

A trough of low pressure is producing a large area of disorganized showers and thunderstorms over the northwestern Caribbean Sea and portions of Central America, and will move northwest across Mexico's Yucatan Peninsula over the next few days. By Sunday night or Monday morning, this activity will push into the Gulf of Mexico, where development into a tropical or subtropical depression could occur. However, an upper-level trough of low pressure over the Western Gulf of Mexico next week will likely bring high wind shear to the Gulf, limiting the potential for any system in the Gulf to strengthen, and our top three models for predicting tropical cyclone genesis are showing little development of this system once it reaches the Gulf. The system will get pulled northwards to affect the U.S. coast from Louisiana to the Florida Panhandle by Tuesday, bringing heavy rains of 2 - 5". In their 8 am EDT Friday Tropical Weather Outlook, NHC gave the disturbance 2-day and 5-day odds of development of 0% and 20%, respectively.

Little change to Ida
There is not much new to say about Tropical Depression Ida, which is wandering slowly over the Central Atlantic, well away from any land areas. Satellite images on Friday morning showed Ida's center of circulation was fully exposed to view by high wind shear, and all of Ida's heavy thunderstorms were limited to the east side of the center. Ida will continue to move slowly in a region of weak steering currents for the next five days, and it is possible that high wind shear will destroy the storm by early next week, as suggested by Friday morning runs of the GFS model.


Figure 1. Latest satellite image of Niala.

Tropical Storm Niala forms near Hawaii
Yet another tropical storm has formed in the Central Pacific near Hawaii, where Tropical Storm Niala was named on Friday morning. Niala was headed northwest at 6 mph towards Hawaii at 11 am EDT Friday, and is expected to take a more westerly path over the weekend, passing about 200 miles south of the Big Island on Saturday afternoon. With tropical storm-force winds expected to extend out up to 90 mph from the center at that time, a Tropical Storm Watch may be hoisted for The Big Island on Friday evening. The 11 am EDT Wind Probability Forecast gave a 21% for South Point on the Big Island to receive tropical storm-force winds of 39+ mph from Niala. The bigger threat from the storm will be heavy rain, which could bring dangerous flash floods to the Big Island on Saturday.

Niala is the record 7th named storm to form in 2015 in the North Central Pacific (between 140°W and the Date Line.) According to wunderblogger Dr. Phil Klotzbach, prior to 2015, the previous record for named storms in the North Central Pacific for an entire season was four, set in 1982. The other named storms that formed in the North Central Pacific in 2015 were Malia, Halola, Ela, Iune, Kilo and Loke. This year's record activity has been due to unusually low wind shear and record-warm ocean temperatures caused by the strong El Niño event underway.


Figure 2. MODIS image of Typhoon Dujuan as seen from NASA's Terra satellite on Friday, September 25, 2015 at 02:15 UTC. Image credit: NASA.

Typhoon Dujuan a threat to Japan, China, and Taiwan
Typhoon Dujuan, a Category 1 storm with 90 mph winds located about 510 miles south-southeast of Okinawa in Japan's Ryukyu Islands at 8 am EDT Friday, is steadily intensifying as it heads northwest at 9 mph towards China. Wind shear is in the moderate range, 10 - 20 knots, and ocean temperatures are a very warm 30°C (86°F), conditions which favor intensification. Satellite loops on Friday morning showed a large, well-organized storm with a 28-mile wide eye and a strong upper-level outflow channel to the south. The Joint Typhoon Warning Center (JTWC) projects that Dujuan will intensify to Category 4 strength by Sunday, and the storm is expected to pass between Okinawa and Miyakojimi island in Japan's Ryukyu Islands near 00 UTC Monday. However, the long-range forecast of where Dujuan might make final landfall is much lower confidence than usual, given a complex upper-level steering pattern the storm is in. The 00Z Friday run of the European model showed a path very close to Taiwan and into mainland China, while the 00Z and 06Z Friday runs of the GFS model had Dujaun missing China entirely, and instead curving to the north and affecting Japan.


Figure 3. Latest satellite image of Invest 93E (left side of image) and 92E (right side of image, close to the coast of Mexico/Central America.)

Tropical disturbances 92E and 93E a heavy rain threat to Mexico and Central America
Our three top models for predicting tropical cyclone genesis predict that an area of disturbed weather about 300 miles south of Acapulco, Mexico (Invest 93E) will develop into a tropical depression on Sunday or Monday. This system is expected to move northwards and be very near the coast close to Acapulco on Monday through Thursday, potentially bringing an extended period of dangerous flooding rains. In their 8 am EDT Friday Tropical Weather Outlook, NHC gave the disturbance 2-day and 5-day odds of development of 30% and 80%, respectively.

Another area of disturbed weather in the Eastern Pacific along the coast near the Mexico/Guatemala border (Invest 92E) is drifting slowly to the northwest, and will bring heavy rains to El Salvador, southern Guatemala, and southeastern Mexico over the next few days. None of our reliable models for forecasting tropical cyclone genesis develop 92E into a tropical depression. In their 8 am EDT Friday Tropical Weather Outlook, NHC gave the disturbance 2-day and 5-day odds of development of 20%.

Apparent tornado near Charleston; heavy rain, coastal flooding on tap for mid-Atlantic
Coastal flooding and heavy rains will be a concern throughout the upcoming weekend over parts of the mid-Atlantic coast, as a long fetch of strong wind gets funneled between high pressure building over the Northeast and a persistent zone of low pressure hugging the Southeast coast. A weak upper-level low drifting across Georgia on Friday will provide support for occasional strong thunderstorms, especially near the coast. One intense cell tracking north-northwest near Charleston, SC, apparently spawned a long-lived tornado early Friday that struck the communities of Johns Island and West Ashley, just a few miles southwest of Charleston. Numerous trees are down, and at least a dozen homes appear to have been damaged, according to the Associated Press. The National Weather Service in Charleston is planning a damage survey for Friday. In two METAR reports, the NWS office indicated a lightning-illuminated tornado just southwest of the office between 12:59 and 1:37 a.m. EDT Friday morning. During the preceding half hour, a significant debris signature was apparent on dual-polarization NWS/NEXRAD radar, as posted in @USTornadoes. The NOAA Storm Prediction Center was projecting a marginal risk of severe weather across far eastern North Carolina on Friday, with a small chance of a brief tornado.


Figure 4. Radar imagery from the NWS NEXRAD radar near Charleston, SC, at 0450 GMT (12:50 am EDT) on Friday, September 25, 2015. A diffuse hook echo is evident in the precipitation signature (left), in the same location as a strong contrast in inbound and outbound winds, shown by closely packed green and red echoes (right). These radar indications of a possible tornado are consistent with reports of tornado damage early Friday morning from just southwest of Charleston. Image credit: NWS/Charleston.


Figure 5. Predicted 72-hour rainfall amounts from 1200 GMT (8:00 am EDT) Friday, September 25, through Monday, September 28. Image credit: NOAA Weather Prediction Center.

This weekend’s multiday spell of wet weather should bring some welcome relief from gradually intensifying drought conditions across parts of the Carolinas and Virginia. However, it will also torpedo weekend recreation for thousands of people. Given the dismal forecast, organizers of the 42nd annual Neptune Festival in Virginia Beach, VA, have cancelled many of this weekend’s events, with other activities moved indoors.

Persistent easterly winds, perhaps as strong as 30-40 mph by Saturday evening into Sunday (see Figure 6 below), will lead to strong rip currents and mostly minor but persistent coastal flooding from New Jersey to the Carolinas. The approaching full moon (see below) will add to the problem by boosting peak tidal levels. Water could be 2 to 3 feet above normal in spots, and 6’ – 9’ surf will be widespread. This prolonged event could produce a substantial amount of beach erosion, especially along the Outer Banks of North Carolina. The islands have long struggled against erosion events that scrub sand from heavily touristed beaches, and long-term sea level rise is only adding to the problem. Barrier islands are naturally fluid structures--they build sand on one side as it disappears on the other--so any effort to preserve specific structures and beaches along barrier islands can be a never-ending battle. Structures such as groins, walls that extend perpendicular to the coast, can help retain sand upstream of prevailing longshore flow, but they typically exacerbate erosion downstream. in 2011, North Carolina ended a decades-long ban on terminal groins, which are placed next to inlets. At least four terminal groins are now being installed or planned along the Outer Banks.


Figure 7. Wundermap depiction of forecast surface winds at 0000 GMT Sunday (8:00 pm EDT Saturday) shows a long fetch of sustained 30-40 mph winds pushing into the mid-Atlantic coast.


September heat still at record pace in Colorado, NYC, New England
It may be autumn, but the atmosphere hasn’t gotten the memo across large parts of the lower 48 U.S. states. The rest of this month will skew warm and dry as a sprawling upper-level ridge predominates, which raises the odds of a record-warm September for the nation as a whole and for a number of U.S. cities. The table below has been updated from a post last week; it shows how warm the remainder of the month will need to be in various cities in order to set a September record. If the NWS forecasts from Thursday are reasonably correct, then much of New England--including Portland, Maine, and Burlington, Vermont--will end up with a record-warm September. New York City’s Central Park also has a good shot. Some intrusions of cool air into the Midwest have tamped down the odds of record monthly warmth in places like St. Louis and Minneapolis. However, the entire Front Range of the Rockies from Pueblo, Colorado, to Cheyenne, Wyoming, is right on track for its warmest September in records dating back more than a century.




Moon mania! Sunday night to bring a rare combo of supermoon and total lunar eclipse
Between 10:11 and 11:23 pm EDT on Sunday night, an unusually large “supermoon” will be completely eclipsed by Earth’s shadow, leading to a rare treat for astronomical buffs. Partial or total eclipses occur only when the Sun, Earth and moon are lined up, so by definition they only occur when the moon is full. Because the moon’s orbit around Earth is not perfectly symmetric, the moon is sometimes closer to us than at other times. Supermoons can appear as much as 14% larger in diameter than usual. There are typically two to five partial or total lunar eclipses per year, but getting a total lunar eclipse (also called a “blood moon,” referring to the common reddish hue) during a supermoon is a once-in-several-decades event. According to space.com, the last one was in 1982 and the next one won’t occur until 2033. Sunday night will also mark the fourth consecutive total eclipse without any partial eclipses, an unusual event called a tetrad.


Figure 8. The total lunar eclipse of October 8, 2014, as photographed in California by Alfredo Garcia, Jr. Image credit: Wikimedia Commons/Tomruen.


Sunday’s lunar eclipse is timed especially well for the Americas, with totality falling between 7 pm and midnight across the contiguous U.S. Evening skies will be fair or clear over much of the nation, apart from the stubborn Southeast storm and another cloud-bearing system over the north central states. Space.com is offering “full ‘blood moon’ coverage” this weekend. Have a great one!

Jeff Masters and Bob Henson


Hurricane Tornado Flood

Heavy Rain, Strong Winds for Southeast U.S. Coast; TD 16-E Remnants Drench Omaha

By: Jeff Masters and Bob Henson , 4:38 PM GMT on September 24, 2015

An elongated area of disturbed weather along the Southeast U.S. coast from Georgia to North Carolina is bringing heavy rains to the coast, but is not a danger to become a tropical storm due to high wind shear of 30 - 40 knots. However, the storm's impact will be similar to that of a weak tropical storm, with heavy rains of up to 5" predicted along the North Carolina coast and strong onshore winds that will bring battering waves and flooding. Long range radar out of Charleston, SC is showing that an area of low pressure (formerly tracked as Invest 97L by NHC) is moving slowly towards the coast, bringing heavy rain. This low will move ashore over South Carolina by Friday. Farther to the north, the Outer Banks of North Carolina are under a High Surf Advisory for waves of 6 - 9 feet; a storm surge of 2 - 3 feet is expected to potentially cause overwash on the only road connecting the vulnerable barrier islands to the mainland, U.S. Highway 12.


Figure 1. Latest regional radar image for the Southeast U.S.


TD 16E remnants help drench Omaha
After bringing heavy rains to parts of the Arizona/New Mexico desert, the remnants of Tropical Depression 16E joined forces with an upper-level trough to produce one of the wettest days in the history of the Omaha, Nebraska area. The heaviest complex of thunderstorms—which developed just northeast of the approaching 16E remnants--parked across the Missouri Valley of Nebraska and Iowa, dumping huge amounts of rain in a fairly localized area over the early morning hours on Wednesday. Omaha’s Eppley Airfield picked up 3.75” in just four hours, and a WU personal weather station in Council Bluffs, Iowa, notched 7.88” in six hours. Lighter showers and storms persisted into Thursday morning along the same corridor, while upper-level energy associated with the 16E remnants evolved into an apparent mesoscale convective vortex across Nebraska and South Dakota. Using NOAA's HYSPLIT trajectory model, which analyzes the source of air masses at various heights, weather.com's Nick Wiltgen found that the upper-level moisture associated with these rains was clearly related to TD 16E, while lower-level moisture came mainly from the Gulf of Mexico and other sources.

Omaha’s calendar-day rainfall on Wednesday totaled 5.74”, making it the fourth-wettest day in the city’s weather history going back to 1871. Impressive amounts of rain also fell in north-central Nebraska and south-central South Dakota, where CoCoRaHS reports ranged as high as 5.95” in southeast Lyman County, SD. It was still raining lightly in Omaha on Thursday morning, with another 0.21” falling between midnight to 10 am CDT. The wettest calendar day on record in Omaha was August 7, 1999, when 6.46” fell, while the total of 10.48” on August 6-7 was the city’s biggest soaking in any 24-hour period. There were no reports of major flood damage in the Omaha/Council Bluffs area on Wednesday, although many residents had to deal with partially submerged vehicles.


Figure 2. The Omaha-area NWS NEXRAD radar at 6:58 am Wednesday, September 22, shows an intense complex of thunderstorms focused across the Omaha metropolitan area. Image credit: NCAR/RAL Real-Time Weather Data.


Figure 3. Rainfall on Wednesday, September 22, at a wunderground PWS in Council Bluffs, Iowa, totaled 8.28”, with another 0.22” (not shown) falling on Thursday as of 10:30 am CDT.


Figure 4. In Ottosen, Iowa, intense thunderstorms extending toward central Iowa from the Missouri Valley on Wednesday morning, September 23, 2015, led to what wunderphotographer Zeman88 dubbed “easily the best sunrise I have ever seen on my way to work as it filled nearly the entire eastern sky.” Image credit: wunderphotographer zeman88.



Figure 5. Thick clouds from heavy thunderstorms to the southeast of Fort Pierre, SD, sweep into the area at sunset on Wednesday, September 23, 2015. Image credit: wunderphotographer Tandistar.

Gulf of Mexico storm next week
A southerly flow of moisture from the Western Caribbean and Southern Gulf of Mexico towards the northern Gulf of Mexico will develop this weekend, and our top three models for forecasting tropical cyclone genesis are showing an area of low pressure capable of becoming a tropical or subtropical depression forming near Mexico's Yucatan Peninsula on Sunday evening. An upper-level trough of low pressure over the Western Gulf of Mexico next week will likely bring high wind shear to the Gulf, limiting the potential for any system in the Gulf to strengthen. The models are currently predicting that this system will get pulled northwards to affect the U.S. coast from Louisiana to the Florida Panhandle by Tuesday. Regardless of whether or not this system develops into a named storm or not, the central Gulf Coast can expect heavy rains from Monday night through Wednesday. In their 8 am EDT Thursday Tropical Weather Outlook, NHC gave the disturbance 2-day and 5-day odds of development of 0% and 20%, respectively.

Ida weakens to a tropical depression
Persistent wind shear has taken its toll on Ida, which is now a tropical depression wandering slowly over the Central Atlantic, well away from any land areas. Satellite images on Wednesday morning showed Ida's center of circulation partially exposed to view by high wind shear, and all of Ida's heavy thunderstorms limited to the southeast side of the center. Ida will continue to move slowly in a region of weak steering currents for the next five days, and it is possible that high wind shear will destroy the storm by early next week, as suggested by Thursday morning runs of the GFS model.


Figure 6. Latest satellite image of Tropical Storm Ida.

Tropical Storm Dujuan a threat to Japan, China, and Taiwan
Tropical Storm Dujuan, located about 620 miles southeast of Okinawa in Japan's Ryukyu Islands at 8 am EDT Thursday, appears destined to become a major typhoon that will threaten Japan, China, and Taiwan early next week. Wind shear has dropped over the past day, and satellite loops on Thursday morning showed the storm was larger and more organized, with increasing spiral banding, the beginnings of an eyewall, and upper-level outflow channels opening to both the north and the south. The Joint Typhoon Warning Center (JTWC) projects that Dujuan will rapidly intensify to Category 4 strength by Sunday, and our top track model forecasts show Dujuan passing between Okinawa and Miyakojimi island in Japan's Ryukyu Islands near 21 UTC Sunday. However, the long-range forecast of where Dujuan might make final landfall is much lower confidence than usual, given a complex upper-level steering pattern the storm is in. Landfall is likely to occur somewhere along the Chinese coast from just north of Taiwan to just south of Shanghai, on Tuesday evening (U.S. EDT time.)


Figure 7. In this image of the Pacific Ocean taken at the exact time of the fall equinox, Wednesday, September 23 at 4:20 am EDT, we see Tropical Storm Dujuan at the right side of the image. The equinox marks the day that every place on Earth receives exactly twelve hours of daylight. From now until the spring equinox, the North Pole will be in 24-hour night, and the South Pole will have 24-hour daylight. Image credit: Dan Lindsey, NOAA/CIRA.

Tropical disturbance south of Acapulco, Mexico a threat to the coast
Our three top models for predicting tropical cyclone genesis predict that an area of disturbed weather about 300 miles south of Acapulco, Mexico will develop into a tropical depression on Monday. This system is expected to move northwards and be very near the coast close to Acapulco on Tuesday, potentially bringing dangerous flooding rains. In their 8 am EDT Thursday Tropical Weather Outlook, NHC gave the disturbance 2-day and 5-day odds of development of 20% and 80%, respectively.

Jeff Masters and Bob Henson

Hurricane Extreme Weather

Potential Gulf of Mexico Development Next Week; Japan Watches TS Dujuan

By: Jeff Masters and Bob Henson , 3:49 PM GMT on September 23, 2015

A southerly flow of moisture from the Western Caribbean and Southern Gulf of Mexico towards the northern Gulf of Mexico will develop this weekend, and our top three models for forecasting tropical cyclone genesis are showing an area of low pressure capable of becoming a tropical or subtropical depression forming near Mexico's Yucatan Peninsula on Monday. An upper-level trough of low pressure over the Western Gulf of Mexico next week will likely bring high wind shear to the Gulf, limiting the potential for any system in the Gulf to strengthen. The models are currently predicting that this system will get pulled northwards to affect the U.S. coast from Louisiana to Florida by next Wednesday, but forecasts this far into the future are low-confidence. In their 8 am EDT Wednesday Tropical Weather Outlook, NHC gave the disturbance 2-day and 5-day odds of development of 0% and 20%, respectively.


Figure 1. Latest long-range radar image from the Cape Hatteras, North Carolina radar.

High seas, strong winds for Southeast U.S. coast
An area of disturbed weather off the coast of North Carolina, which was being tracked by NHC on Tuesday as Invest 97L, is no longer organized enough to be considered an area of interest, but is bringing heavy rains to the waters just offshore from the Outer Banks of North Carolina, where a High Surf Advisory for waves of 6 - 9 feet is posted until Thursday morning. The disturbance is under high wind shear of 30 - 50 knots, and there is plenty of dry air around it, which is preventing development. Long-range radar on Wednesday morning from the Cape Hatteras, North Carolina radar showed no spiral banding or signs of organization to 97L's precipitation echoes. 97L will move slowly west-southwest the next few days, bringing strong winds and occasional heavy rains to the coast of North Carolina on Wednesday, and to the coast of South Carolina on Thursday. None of our three reliable models for predicting tropical cyclone genesis show development of 97L into a tropical or subtropical cyclone.


Figure 2. Latest satellite image of Tropical Storm Ida.

Tropical Storm Ida no threat to land
Tropical Storm Ida continues to wander aimlessly over the Central Atlantic, well away from any land areas. Satellite images on Wednesday morning showed that Ida continued to struggle against moderate wind shear, with the center of circulation partially exposed to view, and all of Ida's heavy thunderstorms limited to the southeast side of the center. Ida will meander slowly today through Thursday, but by Friday, a trough of low pressure passing to its north will likely pull Ida to the north. It appears unlikely that Ida will pose a long-range risk to North America.

Tropical Storm Dujuan a threat to Japan
Tropical Storm Dujuan, located about 700 miles southeast of Okinawa in Japan's Ryukyu Islands at 8 am EDT Wednesday, appears destined to become a major typhoon that will threaten Japan early next week. High wind shear of 20 - 25 knots has kept Dujuan somewhat disorganized, despite warm sea-surface temperatures. However, the storm should move into the southwest corner of an upper-level ridge by Thursday, allowing wind shear to drop and a strong upper-level outflow channel to develop, promoting possible rapid intensification. The Joint Typhoon Warning Center (JTWC) projects that Dujuan will intensify to Category 3 strength and pass near Okinawa island near 00 UTC Monday. However, this forecast is much lower confidence than usual, given a complex upper-level steering pattern that will develop this weekend. We have models showing a weak Dujuan passing well south of Okinawa, and models showing a stronger typhoon recurving and missing the Ryukyu Islands entirely. JTWC is taking a middle approach, and it remains to be seen if this will be correct.

It's been a remarkably active typhoon season in the Western Pacific; Dujuan is the 21st named storm so far in 2015. According to statistics from Digital Typhoon, only six other typhoon seasons since 1951 have had more than 21 named storms by this point in the season. An average season has 26 - 27 named storm during the entire year.

Fall is here!
The September equinox (also called the southward or autumnal equinox in the Northern Hemisphere) arrived on Wednesday morning at 4:21 am EDT. This is the latest September equinox since 2011. Very rarely, it can occur on September 24: the last time this happened was in 1931, and the next time will be in 2303. Happy autumn--or happy spring, if you're south of the equator!

Bob Henson and Jeff Masters

Hurricane

Carbon Dioxide and Climate: What We Knew Then, What We Know Now

By: Bob Henson , 7:05 PM GMT on September 22, 2015

We’re in the midst of a landmark period for our changing climate: the warmest year thus far in the warmest decade in global records of surface air temperature. This is also a crucial time for dialogue on climate change, as we approach a major UN meeting in Paris this December. At that meeting, delegates from around the world will try valiantly to hammer out the first entirely new global agreement in 17 years for reducing greenhouse-gas emissions. We can expect a steady drumbeat of events building up to Paris. This week, Pope Francis is expected to bring his extraordinary message on climate change to the halls of Congress in an address on Wednesday, with a massive rally for climate action scheduled for Washington, D.C., that same day. The pope then heads to New York for a Thursday address at the United Nations, where more than 150 world leaders at a summit on sustainable development are set to adopt 17 ambitious goals, one of which is “take urgent action to confront climate change and its impacts.”

Motivating all this activity is the inexorable build-up of carbon dioxide and other greenhouse gases in our global atmosphere as a result of burning fossil fuels (coal, oil, and gas). When fossil fuels are burned, carbon from the fuel joins with an oxygen molecule from the air to create CO2. Because carbon dioxide is odorless and invisible, it’s all too easy to ignore. People had a harder time ignoring the “emissions” when our land-based transportation was conducted by horse-drawn wagon!

Despite its literal invisibility, carbon dioxide is all too real a substance, and fossil fuels add a tremendous amount of it to our atmosphere. Figure 1 shows how global CO2 emissions have unfolded over the last forty-plus years (up through 2013, the most recent year with complete data). The graphic, created by WU’s Jerimiah Brown using data from the Netherlands Environmental Assessment Agency, tells us much about the situation leading to the upcoming talks in Paris.


Figure 1. Annual emissions of the greenhouse gas carbon dioxide produced by fossil fuel use and cement manufacture over the period 1970 - 2015. Cement production is only a small portion of this total, now around 5% annually. Image credit: Jerimiah Brown, Weather Underground, using data from the Netherlands Environmental Assessment Agency. Here is a high-resolution PDF version of the graphic.


A few things jump out from Figure 1:

--Global emissions are still climbing. In the year 2013, fossil fuel use and cement production put an estimated 35.3 billion metric tons of CO2 into the air (a metric ton is about 10% greater than a U.S. ton). That’s more than twice the amount emitted in 1970. Cement production is only a sliver of this total--historically about 2-3%, but now closer to 5%. Roughly 46% of the annual emissions shown in the graphic remain in the atmosphere each year, with the rest absorbed fairly promptly by oceans and land areas. As evident on the bottom half of Figure 1, emissions can drop slightly from one year to the next, as they did during the recessions of the early 1980s, early 1990s, and late 2000s. However, each recovery has led the way to still-higher global CO2 emissions. And even when the emissions do drop slightly in a given year, carbon dioxide continues to build up in the atmosphere, just as your credit-card balance goes up even when you cut back on how much you put on your card. This is why the amount of CO2 in the global atmosphere has increased every year since regular measurements began in 1958.

--Nation by nation, the United States no longer leads the pack. Back in the late 1990s, the U.S. was responsible for about 30% of global CO2 emissions, while China represented about 15%. Now the roles have switched as a result of China’s breakneck pace in manufacturing and development. In 2013, China was responsible for roughly 29% of global CO2 emissions, with the U.S. at around 15%. A substantial part of China’s CO2 emissions is the result of items being manufactured for sale in the United States and elsewhere; here’s a very helpful analysis from Carbon Brief on how this affects the global picture.

--Per capita, the U.S. is still in the driver’s seat. Because the United States has less than a quarter of China’s population, the amount of CO2 emitted per person is more than twice as much in the U.S. versus China. A few oil-producing nations in the Middle East have even higher per-capita rates, but their small populations means that they produce far less CO2 overall than the United States.

--Decades of emissions add up. When the atmosphere's stock of carbon dioxide goes up, it takes several hundred years for the oceans to absorb about 75 percent of this excess. The remaining 25 percent or so is stuck in the atmosphere for much longer--some of it for more than 100,000 years. This is why emissions from decades ago still have a big impact on climate. The list at upper left of Figure 1 shows the cumulative emissions from six top emitters, plus the 28 nations that now make up the European Union (EU28). Of the total amount of CO2 put into the air from 1970 to 2013, the US is responsible for about 22%; the EU28, about 18%; and China, about 15%. If you go back before 1970, the United States has an even larger share of the pie.

--Progress is possible. As a group, the EU28 nations are now emitting about 14% less CO2 than they were in 1990. That’s noteworthy when you consider that the EU28’s population and level of development is roughly comparable to the United States’. Back in the early 1980s, the US and EU28 had nearly identical CO2 emissions. By 2013, the US annual total was about 43% more than the EU28’s.

Commentary: what it means for the Paris talks

Whatever emerges in Paris is likely to be much different than the only global-scale agreement to date on carbon emissions: the Kyoto Protocol. Created in 1998, Kyoto was hamstrung by understandable tension between developed countries (the U.S. in particular) and developing nations (especially China and India). Many participants from around the globe felt it was unfair to restrict the right of less-prosperous countries to use fossil fuel to grow their economies after rich nations had had virtually unlimited access to it. The resulting agreement largely held back from emission restrictions for the developing world--and in response, the U.S. Congress voted 98-0 not to ratify Kyoto. The upshot is that most of the world’s economic activity since 1998 has taken place outside the bounds of the protocol, leaving the door wide open for huge global increases in CO2 emissions. Meanwhile, the European Union did even better than its Kyoto pledge, cutting its emissions of the top greenhouse gases 18% below 1990 levels by 2012.

Given the trends in Figure 1, a Kyoto-style approach clearly won’t work this time around. Any global agreement on emissions needs to include both the United States and China, as well as fast-growing India, in order to be effective. Yet it’s hard to imagine the current U.S. Congress agreeing to any globally constructed emissions cuts. Given this constraint and others, a new strategy has taken shape: each nation is coming up with its own nonbinding “pledges,” which will be enforced largely through peer pressure and perhaps eventually through economic tools such as tariffs and sanctions. An unprecedented agreement between China and the United States late in 2014 led to pledges by China to maximize its greenhouse gas emissions no later than 2030 (though this would still allow China’s total emissions to increase for more than a decade) and by the U.S. to reduce its emissions 12-19% below 1990 levels by 2025 (including emissions related to land use and forestry, which complicates the picture somewhat). Earlier this month, a group of some of the largest cities of China and the United States agreed on emission targets that in some cases are even more ambitious than the national goals.

Historic as they are, these examples above show how a patchwork of nation-by-nation agreements may end up resembling a crazy quilt. The big question facing delegates to Paris is whether such a global set of voluntary emission cuts, even if they’re adhered to, will be enough. There’s no single bright line that separates a livable climate from one riddled by disaster, but for more than 15 years, many scientists and policymakers have worked toward the commonly cited goal of no more than a 2°C global temperature rise above pre-industrial levels. In June, an analysis by the International Energy Agency showed that the combined global pledges thus far would allow a temperature rise of 2.6°C by 2100 and 3.5°C in the 2200s. Such a rise would boost the odds of irreversible physical change, such as the unstoppable melting of ice sheets. It would also raise the risk of truly serious impacts on agriculture, water and food supply, and human health, raising the specter of increased conflict and climate refugees. Some analysts are already pointing to the role of record drought in Syria as a major factor in that nation's civil war and the subsequent flood of migrants. "News reports calling the refugees the first 'climate refugees' are getting too far ahead of the curve," asserted Andrew Freedman in Mashable. "But the ongoing humanitarian disaster provides a teaching opportunity for a time not too long from now when the first true climate refugees trigger a similar situation."

New discoveries of oil, coal, and gas in recent years have led to unexpectedly abundant supplies of fossil fuel. Yet if we want to be fairly confident of avoiding the 2°C benchmark, we can only burn a small fraction of this fossil fuel--only about 20%, according to one influential estimate that was reinforced by the IPCC in 2013. Any global agreement that keeps us near the 2°C goal will indirectly force the vast majority of the world’s proven oil, coal, and gas reserves to remain in the ground. Ultimately, this would be a conservative action in the truest sense--conserving fossil fuel--but some of the world’s largest and most powerful corporations would stand to lose trillions of dollars in value if this played out. We know that at least one major firm had some sense of the dilemma more than 30 years ago. An major investigative report by Inside Climate News, now being published as a multipart series, describes how Exxon carried out extensive observational and computational research, starting as far back as the 1970s, that pointed to the huge risks posed by increasing carbon dioxide.

We now know that massive amounts of energy can be produced apart from fossil fuels, with the costs steadily dropping. A group of eminent British scientists and policy leaders has called for a Global Apollo Program--an international 10-year R&D effort to make renewable energy more affordable than fossil fuel. Such efforts will go a long way toward giving any global agreement cobbled together in Paris a fighting chance to succeed.

Dr. Ricky Rood is attending a Climate Data Summit sponsored by the Risky Business project as part of Climate Week NYC. See his WU blog post from September 19 for more about the long and very winding road to the negotiations in Paris. My post with Jeff Masters from earlier today outlines current happenings in the tropics; we'll be back with more on Wednesday.

Bob Henson

Climate Change Politics Climate Change

Invest 97L off Southeast U.S. Coast; Tropical Storm Ida Churns the Central Atlantic

By: Bob Henson and Jeff Masters , 3:43 PM GMT on September 22, 2015

An area of disturbed weather off the coast of North Carolina (Invest 97L) is bringing heavy rains to the waters just offshore from the Outer Banks of North Carolina, where a High Surf Advisory for waves of 6 - 9 feet is posted. The disturbance is under high wind shear of 20 - 30 knots, and there is plenty of dry air around it, which is inhibiting development. Satellite loops on Tuesday morning showed that 97L had some rotation but no surface circulation, and a modest area of heavy thunderstorms that were increasing in intensity and areal coverage. Long-range radar on Tuesday morning from the Cape Hatteras, North Carolina radar showed no spiral banding or signs of organization to 97L's precipitation echoes. 97L will move slowly west-southwest the next few days, bringing strong winds and occasional heavy rains to the coast of North Carolina Tuesday and Wednesday, and to the coast of South Carolina on Wednesday and Thursday. An upper-level trough of low pressure along the U.S. East Coast will bring high wind shear over 97L for the remainder of the week, which will make development difficult. None of our three reliable models for predicting tropical cyclone genesis show development of 97L into a tropical or subtropical cyclone. In their 8 am EDT Tuesday Tropical Weather Outlook, NHC gave the disturbance 2-day and 5-day odds of development of 10% and 20%, respectively.


Figure 1. Latest long-range radar image from the Cape Hatteras, North Carolina radar.


Tropical Storm Ida no threat to land
Tropical Storm Ida is essentially stalled out over the Central Atlantic, well away from any land areas. Satellite images on Tuesday morning showed that Ida continued to struggle against moderate wind shear, with the center of circulation partially exposed to view, and all of Ida's heavy thunderstorms limited to the southeast side of the center. Ida will meander slowly today through Thursday, but by Friday, a trough of low pressure passing to its north will likely pull Ida to the north. It appears unlikely that Ida will pose a long-range risk to North America.


Figure 2. Latest satellite image of Tropical Storm Ida.

Gulf of Mexico development next week?
A southerly flow of moisture from the Western Caribbean and Southern Gulf of Mexico towards the northern Gulf of Mexico will develop this weekend, and the long-range forecasts from the GFS and European models are showing an area of low pressure capable of becoming a tropical or subtropical depression forming near Mexico's Yucatan Peninsula on Monday. Wind shear is likely to be moderate to strong over the region, limiting the potential for this system to strengthen. The models are currently predicting that this system will get pulled northwards to affect the U.S. coast from Louisiana to Florida by the middle of next week, but a strong trough of low pressure over the Western Gulf of Mexico will likely bring high wind shear to the Gulf, limiting the odds of a this system becoming a tropical or subtropical storm that will hit the U.S. next week.

Tropical Storm Malia moving through Central Pacific
Tropical Storm Malia formed on Monday and moved though the Papahanaumokuakea Marine National Monument, several hundred miles west of the Hawaiian Islands. Malia is headed north-northwestwards at 8 mph and will likely become an extratropical storm on Wednesday, between Hawaii and Alaska's Aleutian islands. Malia was the record 6th named storm to form in 2015 in the North Central Pacific (between 140°W and the Date Line.) According to wunderblogger Dr. Phil Klotzbach, prior to 2015, the previous record for named storms in the North Central Pacific for an entire season was four set in 1982. The other named storms that formed in the North Central Pacific in 2015 were Halola, Ela, Iune, Kilo and Loke. This year's record activity has been due to unusually low wind shear and record-warm ocean temperatures caused by the strong El Niño event underway.

TD 16E’s rains less than expected in Southwest
After moving into northwest Mexico on Monday, Tropical Depression 16E quickly dissipated, with no discernable surface circulation detectable in the depression’s remnants over Arizona by early Tuesday morning. The remnants are now being swept northeastward in fast upper-level flow between a ridge over Texas and a persistent upper low over southern California. Between the system’s rapid motion and disorganized state, plus drier air infiltrating at upper levels, the rainfall associated with TD 16E’s remnants was less intense and widespread than earlier expected. Reports from CoCoRaHS observers on Tuesday morning for the preceding 24 hours showed most of the Phoenix area getting little more than sprinkles, with about 0.45” recorded on the eastern fringes of the metro area. Reports in the Tuscon area ranged from about 0.5” to more than 1.5”, with around 3” recorded well south of town in Santa Cruz County. Nogales, AZ, picked up 1.99”. Further west, the upper-level low over southern California was another underperformer in terms of rainfall. The San Diego area received just trace amounts, and the Los Angeles metroplex stayed high and dry.


Figure 3. Washes quickly filled up in Tuscon, AZ, as rains associated with the remnants of TD 16E reached town on Monday, September 21, 2015. Image credit: wunderphotographer pjkace70.


Figure 4. Heavy rains sweep across the countryside southwest of Phoenix near Gila Bend, AZ, on Monday, September 21, 2015. Image credit: wunderphotographer Milker13.

Another Pacific typhoon may develop this week
Tropical Depression 21W, located more than 300 miles west of the Marianas Islands in the open Northwest Pacific, appears destined to become the region’s 21st named storm and 13th typhoon of 2015. Moderate wind shear has kept 21W somewhat disorganized, despite warm sea-surface temperatures: convection is focused to the west of the ill-defined center of circulation. TD 21W should move into a more favorable spot on the southwest corner of an upper-level ridge by midweek. The Joint Typhoon Warning Center projects that TD 21W will be a recurving Category 4 typhoon by Sunday. It is too early to know whether the expected recurvature will be sharp and soon enough to spare Japan or neighboring areas from any typhoon-related impacts. This year has been exceptionally busy in the Northwest Pacific: as of mid-August, the region had broken its record for the greatest amount of accumulated cyclone energy for any year since 1950.

Wunderblogger Steve Gregory has an update on El Niño in his Monday afternoon post. Later today, we’ll have a post on this week’s climate-related events in Washington, D.C., and New York and how carbon dioxide emissions have evolved over the last four-plus decades.

Bob Henson and Jeff Masters


Figure 5. Latest satellite image of Tropical Depression 21W.

Hurricane

TD 16E Bringing Heavy Rain to Southwest; Tropical Storm Ida Stalling at Sea

By: Jeff Masters and Bob Henson , 3:43 PM GMT on September 21, 2015

Tropical Depression 16E, which formed on Sunday just southwest of Baja California, crossed the peninsula on Sunday night and made a second landfall Monday morning on the east side of Mexico’s Sonoran state, near Tiburón Island. The low- and upper-level circulations associated with TD 16E have decoupled in the grip of southwesterly wind shear, and the depression will become a post-tropical/remnant low in the next few hours as it moves northeast across Mexico, eventually reaching east-central Arizona by Tuesday morning. Meanwhile, a weak upper-level low roughly 300 miles southwest of Los Angeles has produced a separate cluster of thunderstorms with prolific lightning. This complex of storms was located just offshore of Southern California on Monday morning, moving northwest parallel to the coast.


Figure 1. This water-vapor satellite image from 1330Z (9:30 am EDT) on Monday, September 22, 2015, shows two distinct rain producers: an upper-level low (left, southwest of California) and Tropical Depression 16E (right, over northwest Mexico): Image credit: NHC.


TD 16E dumped several inches of rain as it passed over Baja California. Geary's webcam on the Sea of Cortez in central Baja captured dramatic images of the storminess on Sunday afternoon. Geary’s PWS recorded 0.73” of rain on Saturday; 2.36” on Sunday; and 0.40” on Monday morning up through 10 AM EDT. The convection associated with TD 16E is now drenching Sonora, with isolated amounts of up to 12” possible in mountainous areas.


Figure 2. MODIS image of TD 16-E approaching Mexico's Baja Peninsula as seen from NASA's Aqua satellite on Sunday, September 20, 2015. Image credit: NASA.



Figure 3. Flooding in the Central Baja town of San Ignacio, and between Constitucion and La Paz on Sunday, September 20, 2015, from TD 16-E. Image credit: Geary Ritchie. Geary's webcam on the Sea of Cortez in central Baja is capturing some good images of the storm, and his PWS had recorded a 3-day total of 3.49" of rain as of 10 am EDT Monday.


Much of the Southwest U.S. is plastered with flash flood watches for today and/or Tuesday, but the juxtaposition of the upper low with TD 16E complicates the rainfall outlook for the Southwest. Both rainmakers are now tracking a bit southeast of earlier forecasts, which reduces the odds of a widespread soaking rain for the Los Angeles area. From San Diego eastward, the deserts of far southern California could still notch 1-2” from scattered thunderstorms as the upper low swings closer to the area this afternoon into Tuesday. Meanwhile, the focused area of convection associated with TD 16E will bring very heavy rain into southeast Arizona and southwest New Mexico on Monday night into Tuesday, with widespread 1-3” amounts and localized totals of up to 8” where the circulation impinges on south- and east-facing slopes. The only time Phoenix has seen more than 3” of rain in a calendar day was just last year, when 3.30” fell on September 8, 2014, goosed by moisture from former Hurricane Norbert.

As TD 16E deteriorates, the weakening upper low will approach it, ingesting some of its moisture and setting the stage for scattered but intense thunderstorms from southeast California into Arizona, southern Utah, and New Mexico on Tuesday. These rains will be less focused than Monday’s, but pockets of torrential rain, downburst wind, and even small hail can be expected. Recreationalists will need to be especially vigilant on Tuesday: in some areas, it could seem that conditions are improving on Tuesday morning before dangerous weather develops later in the day.


Figure 4. Predicted precipitation for the 5-day period ending Saturday, September 26, 2015. TD 16-E is predicted to bring rainfall amounts of up to four inches to Arizona, with even higher amounts possible in isolated spots. Image credit: National Weather Service.

Tropical Storm Ida no threat to land
Tropical Storm Ida slowed down its forward speed to 6 mph on Monday morning, and is about to essentially stall out for 3 - 4 days over the Central Atlantic, well away from any land areas. Satellite images on Monday morning showed that Ida continued to struggle against moderate wind shear, with the center of circulation partially exposed to view, and all of Ida's heavy thunderstorms limited to the southeast side of the center. Conditions over the next few days favor intermittent strengthening, and Ida could be a hurricane by the end of the week. By the end of the week, a trough of low pressure passing to its north will likely pull Ida to the north, and it appears unlikely that Ida will pose a long-range risk to North America.


Figure 5. Latest satellite image of Tropical Storm Ida.

Gulf of Mexico development next week?
A southerly flow of moisture from the Western Caribbean and Southern Gulf of Mexico towards the northern Gulf of Mexico will develop this weekend, and the long-range forecasts from the GFS and European models are advertising the possibility of a tropical depression forming near Mexico's Yucatan Peninsula by next Monday. Wind shear is likely to be moderate to strong over the region, limiting the potential for this system to strengthen. The eventual track of such a storm so far in the future is highly uncertain; it could potentially stay trapped in Mexico's Bay of Campeche and only affect Mexico, or get pulled northwards to affect the U.S. coast from Louisiana to Florida. Stay tuned.

Tropical Storm Malia forms in the Central Pacific
Tropical Storm Malia formed on Monday morning in the waters several hundred miles west of the Hawaiian Islands. A Tropical Storm Warning has been issued for central portions of the Papahanaumokuakea Marine National Monument, from French Frigate Shoals to Maro Reef to Lisianski Island. Malia is headed north-northeastwards at 11 mph on a path that will take it midway between Hawaii and Alaska's Aleutian islands late this week.

Malia is the record 6th named storm to form in 2015 in the North Central Pacific (between 140°W and the Date Line.) According to wunderblogger Dr. Phil Klotzbach, prior to 2015, the previous record for named storms in the North Central Pacific for an entire season was four set in 1982. The other named storms that formed in the North Central Pacific in 2015 were Halola, Ela, Iune, Kilo and Loke. This year's record activity has been due to unusually low wind shear and record-warm ocean temperatures caused by the strong El Niño event underway.

Jeff Masters and Bob Henson

Hurricane

Flash Floods Likely in Arizona and California From 91E; Atlantic Threats are Minimal

By: Jeff Masters , 4:44 PM GMT on September 20, 2015

An area of disturbed weather off the coast of Mexico's Baja Peninsula (Invest 91E) is headed north at 15 mph, and will likely make landfall on the central Baja coast on Monday morning. Satellite images of 91E on Sunday morning showed plenty of moisture and heavy thunderstorms were associated with 91E, though this activity was not well-organized enough to be declared a tropical depression. In their 8 am EDT Sunday Tropical Weather Outlook, NHC gave the disturbance 2-day and 5-day odds of development of 70%. Moisture from this system will produce heavy rains across portions of the Baja California Peninsula and northwestern mainland Mexico through Tuesday, potentially causing dangerous flash flooding and mudslides. An impressive surge of moisture 91E will bring some of the highest levels of water vapor ever recorded in September to Southern California and Arizona beginning on Monday and extending into Tuesday. This rich tropical moisture will very likely cause dangerous flash flooding; the NWS is predicting that up to four inches of rain could fall in portions of Arizona, which is a very extreme amount of rain for this desert region. Daniel Swain's excellent California Weather Blog noted on Saturday evening that this week's rains from 91E could cause September 2015 to set some all-time monthly precipitation records in Southern California, thanks to rains last week from the remnants of Hurricane Linda. Those rains led to flash flooding that killed 19 people in the Utah/Arizona border region.

Geary's webcam on the Sea of Cortez in central Baja is capturing some good images of the storm, and his PWS has recorded 1.03" of rain as of 5 pm EDT Sunday.


Figure 1. Latest satellite image of 91E.


Figure 2. Predicted precipitation for the 7-day period ending Sunday, September 30, 2015. 91E is predicted to bring rainfall amounts of up to four inches to Arizona. Image credit: National Weather Service.

Invest 96L off Southeast U.S. coast little threat
An area of disturbed weather off the coast of North Carolina (Invest 96L) is bringing heavy rains to the waters more than 500 miles offshore of the U.S. East Coast, but is not a major wind or heavy rain threat to the coast. The disturbance is under high wind shear of 20 - 30 knots, and there is plenty of dry air around it, which is inhibiting development. Satellite loops on Sunday morning showed that 96L had a weak and very elongated surface circulation, and the storm's heavy thunderstorms were poorly organized and far from the center of circulation. Our three reliable models for predicting tropical cyclone genesis showed no development, and NHC has stopped tracking this system as an "Invest" (area of interest]. In their 8 am EDT Sunday Tropical Weather Outlook, NHC gave the disturbance 2-day and 5-day odds of development of 10%. Strong winds from the system will bring high surf to the Outer Banks of North Carolina much of the week.


Figure 3. VIIRS image of the action in the Atlantic as seen by the Suomi satellite taken on Saturday, September 19, 2015. Tropical Depression 9 (TD 9, center) was downgraded to a remnant low by the National Hurricane Center on Saturday afternoon. Image credit: NASA.

Tropical Storm Ida no threat to land
Tropical Storm Ida continued to head west-northwest at 12 mph on Sunday morning, well away from any land areas. Satellite images on Sunday morning showed that Ida was struggling against moderate wind shear, which had exposed the center of circulation to view and kept all of Ida's heavy thunderstorms limited to the east side of the center. Conditions over the next few days favor slow strengthening, with the 12Z Sunday run of the SHIPS model predicting moderate wind shear of 5 - 15 knots, warm ocean temperatures near 28.5°C (83°F), and a moist atmosphere. The long-range fate of Ida is unclear, since the storm will experience a collapse in its steering currents from Monday through Wednesday that will cause a very slow, erratic motion. A strong trough of low pressure passing to its north may be able to pull Ida to the north late in the week, or the storm may stay trapped in the Central Atlantic by weak steering currents.

Tropical Depression 5-C in the Central Pacific
Tropical Depression 5-C is moving north-northeastwards on a path that will take it several hundred miles west of the Hawaiian Islands. Although TD 5-C is fighting high wind shear of 25 - 30 knots, just a slight increase in organization would bring it to tropical storm status, and a Tropical Storm Warning has been issued for central portions of the Papahanaumokuakea Marine National Monument, from French Frigate Shoals to Maro Reef to Lisianski Island. A Tropical Storm Watch has been issued for the area from Lisianski Island to Pearl and Hermes.

Jeff Masters

Hurricane

Watching 96L off South Carolina Coast; Tropical Storm Ida Forms in Central Atlantic

By: JeffMasters, 3:47 PM GMT on September 19, 2015

An area of disturbed weather off the coast of South Carolina (Invest 96L) is bringing heavy rains to the waters from the northern Bahamas to the Outer Banks of North Carolina, but is not a major wind or heavy rain threat to the coast. The disturbance is under high wind shear of 20 - 30 knots, and there is plenty of dry air around it, which is inhibiting development. Satellite loops on Saturday morning showed that 96L had developed a weak surface circulation, but the storm's heavy thunderstorms were removed over 200 miles to the north and east of the center, characteristic of the structure of a subtropical storm. Our three reliable models for predicting tropical cyclone genesis show little or no development, and the 12Z Saturday run of the SHIPS model showed wind shear remaining a high 20 - 30 knots though Monday, which should keep any development slow. In their 8 am EDT Saturday Tropical Weather Outlook, NHC gave the disturbance 2-day and 5-day odds of development of 20% and 40%, respectively. 96L's slow movement to the northeast through Monday should keep the heaviest rains offshore, but strong winds from the system will bring high surf to the Outer Banks of North Carolina. By Tuesday, 96L may move more to the north or north-northwest, bringing the storm close to the U.S. mid-Atlantic coast near Virginia.


Figure 1. Latest satellite image Invest 96L.

Tropical Storm Ida forms
Tropical Storm Ida formed Friday night in the waters of the Central Atlantic midway between the Lesser Antilles Islands and the coast of Africa, and was headed west-northwest at 12 mph on Saturday morning, well away from any land areas. Satellite images on Saturday morning showed that Ida was slowly organizing, but lacked a large area of heavy thunderstorms, and the center of circulation had been exposed to view by high wind shear. Conditions over the next few days favor slow strengthening, with the 12Z Saturday run of the SHIPS model predicting moderate wind shear of 10 - 20 knots, warm ocean temperatures near 28°C (83°F), and a moist atmosphere. The long-range fate of Ida is unclear, since the storm will experience a collapse in its steering currents from Monday through Wednesday that will cause a very slow, erratic motion. The European model predicted with its 00Z Saturday run that Ida would lift out to the north by the middle of the week, caught up in a strong trough of low pressure passing to its north. The GFS model showed that the trough would bypass Ida and leave it stranded in the Central Atlantic to wander for many days. Unless Ida can pull off some non-Euclidian movements like her namesake character in my favorite computer game, Monument Valley, Ida is unlikely to threaten any land areas in North America or the Caribbean.

Ida is the ninth named storm of the 2015 Atlantic hurricane season, which already surpasses the total number of named storms that occurred during the last two strong El Niño events, 1997 (eight named storms) and 1982 (six named storms.) This year's strong El Niño event is different than the previous two, in that we are seeing much lower levels of wind shear over the far Eastern Atlantic, which is allowing storms to form in that region.


Figure 2. Latest satellite image of Tropical Storm Ida.

Tropical Depression Nine near dissipation
Tropical Depression Nine in the Central Atlantic is barely a tropical depression, and is likely to dissipate by Sunday.

Tropical Depression 5-C forms in Central Pacific
Yet another tropical cyclone has formed in the Central Pacific, where Tropical Depression 5-C is moving northwards on a path that will take it several hundred miles west of the Hawaiian Islands. A Tropical Storm Warning has been issued for central portions of the Papahanaumokuakea Marine National Monument, from French Frigate Shoals to Maro Reef to Lisianski Island; a Tropical Storm Watch has been issued for the area from Lisianski Island to Pearl and Hermes.

Invest 91E a heavy rain threat to Baja Mexico
An area of disturbed weather off the coast of Mexico's Baja Peninsula (Invest 91E) is headed north-northwestwards at 10 mph, and will likely make landfall on the central Baja coast on Monday. Moisture from this system will produce heavy rains across portions of the Baja California Peninsula and northwestern mainland Mexico through Tuesday, potentially causing dangerous flash flooding and mudslides. 91E will bring isolated heavy rains to Southern California and Arizona beginning on Monday night.

Jeff Masters

Hurricane

Two Tropical Depressions in Atlantic; More Record Heat in U.S., Europe

By: Bob Henson , 7:27 PM GMT on September 18, 2015

Tropical activity is at a low ebb globally compared to the breakneck pace of the last month. The only hurricane-strength tropical cyclone on the planet as of Friday was Typhoon Krovanh, which peaked at Category 3 strength over the last 24 hours. At 1500 GMT (11:00 am EDT) on Friday, Krovanh was located about 80 miles northeast of the island of Iwo To, gradually recurving to the north and packing top sustained winds of 100 mph. Iwo To and its neighboring islands have seen little impact from Krovanh, as the typhoon's convection and its strongest winds are focused on its east side. Kovanh should be below typhoon strength by Monday as it sweeps well to the east of Japan's main islands.

In the Atlantic, we have two tropical depressions, both far out at sea in the central North Atlantic, as well as a disturbance closer to the southeast U.S. coast. Tropical Depression 9 has missed its chance to become a named storm. Now undergoing southwesterly shear, TD 9 is largely devoid of convection, and statistical and dynamical forecast models generally weaken it over time as it drifts to the west-northwest. The National Hurricane Center is projecting TD 9 to become a remnant low by tonight. Further to the southeast, newborn Tropical Depression 10, also heading west-northwest, has a better chance of becoming a named storm. Models are consistent in bringing TD 10 to tropical storm strength by Sunday and keeping it there for several more days. The track forecast becomes more uncertain after Monday, but the overall tendency is toward a gradual recurvature well east of the Caribbean and North America.


Figure 1. Satellite imagery of water vapor shows the extensive swath of convection associated with Invest 96L (left). Also evident are tiny Tropical Depression 9 (center) and much larger Tropical Depression 10 (right). Image credit: CIMMS/SSEC/University of Wisconsin.

About 100 miles east of Jacksonville, Florida, Invest 96L is a region of surface low pressure associated with an vast, loosely organized area of showers and thunderstorms and a weak surface boundary that extends from south Florida into the Northwest Atlantic. A flood watch is in effect over eastern Florida on Friday, with heavy thunderstorms pounding the populated strip from Miami to Palm Beach. NHC gives Invest 96L a 20% chance of development into a tropical cyclone through Monday and a 40% chance through Wednesday, as the low continues to spin off the southeast U.S. Coast. WIth an upper-level trough predicted to dig over the eastern United States next week, 96L could take on at least some hybrid or subtropical characteristics if it were to intensify. As high pressure builds to the north of 96L, the next few days may bring an extended period of high surf along parts of the U.S. East Coast, especially in the Carolinas.



Figure 2. Surface temperatures on Friday, September 18, 2015, remained far above normal across central Europe, from Italy into western Russia. Image credit: climatereanalyzer.org, University of Maine.

Extreme mid-September heat in Europe
An exceptional summer of record-breaking heat waves across Europe is hanging on with remarkable vigor as the fall equinox approaches. On Thursday, September 17, dozens of locations in at least six countries set all-time high temperature records for any date in September, according to international weather records researcher Maximiliano Herrera. This is truly an amazing accomplishment for so late in a transition month like September when average temperatures are dropping throughout the month. Among the locations that set all-time September highs on Thursday were these four stations in southeast Germany, all of which broke monthly records that had just been set on September 1 of this year (thanks to Michael Theusner, Klimahaus, for these statistics).

Gottfrieding: 34.0°C (93.2°F), old record 32.3°C
Mühldorf: 33.3°C (91.9°F), old record 32.6°C
Straubing : 32.9°C (91.2°F), old record 31.4°C
Chieming: 31.1°C (88.0°F), old record 30.6°C

Still more records fell on Friday, as dozens more stations with long periods of record set all-time September highs, according to Herrera. Sarajevo, the capital of Bosnia and Herzegovina, hit 38.0°C (100.4°F), beating its previous September record of 37.7°C. Weather records in Sarajevo extend back to 1880. Several locations came within 2°F of their all-time highs for any time of year--again, a remarkable outcome for the final week of astronomical summer! Special thanks for these data go to Maximiliano Herrera, who maintains a comprehensive list of extreme temperature records for every nation in the world on his website.

See the Jeff Masters post from Thursday for details on the many heat records set in Europe and elsewhere last month, which was the warmest August in global record-keeping that goes back to 1880.

Warmest September on record for U.S.? It's possible
Summer isn't quite ready to let go of the contiguous U.S., either, as warm weather has predominated in many areas through September. In a swath running from Colorado's Front Range to New England, a number of locations are on track for what could be their warmest September on record. These include:




Figure 3. The 8- to 14-day outlook from the NOAA Climate Prediction Center shows a high probability that most of the contiguous U.S. will have above-average temperatures during the last week of September. Image credit: NOAA/CPC

All of these places, and others around the nation, have a running start toward possibly setting their all-time monthly record for September. One big obstacle in their way is the climatological tendency for temperatures to drop as we move toward the end of the month. However, that tendency will be muted somewhat by persistent upper-level high pressure that's keeping any major pushes of Canadian or Arctic air at bay. NOAA's Weather Prediction Center is projecting high odds of above-normal temperatures across much of the nation for the 8- to 14-day period (see Figure 3). With these positive signals, I won't be surprised to see a number of U.S. cities end up with their warmest September on record. The wide geographic spread of the warmth also suggests that the contiguous U.S. as a whole may be in the midst of its warmest September in more than a century of record-keeping. The just-released autumn/winter outlook from weather.com projects more warmth for October and beyond, especially for the eastern U.S.

Have a great weekend, everyone!

Bob Henson

Hurricane Heat

Earth Has its Hottest Summer and Hottest August on Record

By: Jeff Masters , 4:00 PM GMT on September 17, 2015

August 2015 was Earth's hottest August on record, and the Northern Hemisphere summer period of June-July-August was the hottest summer since record keeping began in 1880, said NOAA's National Centers for Environmental Information (NCEI) on Thursday. NASA rated August 2015 as the 2nd warmest August on record, a scant 0.01°C from tying August 2014's record mark. August 2015's warmth makes the year-to-date period (January - August) the warmest such period on record, according to both NOAA and NASA. NOAA said that August 2015 was the sixth month in 2015 to break its monthly temperature record, joining February, March, May, June, and July. August 2015 tied with January 2007 for the third warmest monthly departure from average of any of the 1628 months since records began in January 1880 (the record warmest departures occurred in February 2015 and March 2015). Over the oceans, August 2015 had the warmest departure from average of any month in the historical record (previous record: July 2015.) A potent El Niño event in the Eastern Pacific that crossed the threshold into the "strong" category in early July continues to intensify, and strong El Niño events release a large amount of heat to the atmosphere, typically boosting global temperatures by at least 0.1°C. This extra bump in temperature, when combined with the long-term warming of the planet due to human-caused emissions of heat-trapping gases like carbon dioxide, makes it extremely likely that 2015 will be Earth's second consecutive warmest year on record. The UK Met Office put out a press release earlier this week predicting that 2016 will continue to see record or near-record levels of global heat, and it is quite possible that Earth will see three consecutive years with record-breaking surface temperatures: 2014, 2015, and 2016.


Figure 1. Departure of temperature from average for August 2015, the warmest August for the globe since record keeping began in 1880. Record warmth was observed across South America and parts of Europe, Asia, and Africa. Record warmth was also over much of the world's oceans, including the waters surrounding Hawaii, where the warm waters are expected to cause a significant coral bleaching episode resulting in a large-scale die-off of coral. Image credit: National Centers for Environmental Information (NCEI) .

Global satellite-measured temperatures in August 2015 for the lowest 8 km of the atmosphere were the 3rd warmest in the 37-year record, according to the University of Alabama Huntsville (UAH). The lowest 8 km of the atmosphere heats up dramatically in response to moderate to strong El Niño events, with a time lag of several months--as occurred during the El Niño events of 1998 and 2010, the only two years that had warmer August temperatures than 2015. Earth's lower atmosphere temperature will likely hit record levels by early 2016.



Two billion-dollar weather disasters in August 2015 in China
Two billion-dollar weather-related disasters hit the Earth last month, both in China, according to the August 2015 Catastrophe Report from insurance broker Aon Benfield: Typhoon Chan-hom ($1.6 billion in damage) and flooding August 20 - 24 that caused $1.2 billion in damage. With fifteen billion-dollar weather disasters through August 2015, Earth is on pace for a below-average number of such disasters, compared to statistics from the past ten years.


Disaster 1. Typhoon Chan-hom made landfall about 80 mi south-southeast of Shanghai, China on August 11, killing 16 people and doing at least $1.5 billion in damage. The typhoon did another $100 million in damage to Guam, Japan, Taiwan, and Korea. In this image, we see people watching huge waves from Chan-hom pounding Wenling, in east China's Zhejiang province, on August 10, 2015. Image credit: STR/AFP/Getty Images.


Disaster 2. Heavy rainfall in China from August 20 - 24 killed 28 people and did $1.2 billion in damage. More than 238,000 residents were evacuated as floods and landslides destroyed 7,770 homes and damaged 35,100. In this picture, we see vehicles stranded on a flooded road in Wuhan, Hubei Province of China, on August 23, 2015, when 160.2 millimeters (6.31") hit the city. This was their heaviest daily rainfall since 1998, according to Changjiang Times. Image credit: ChinaFotoPress/Getty Images.

Most expensive disaster in Dominica's history
August 2015 also saw one nation experience its most expensive disaster in its history: the Caribbean island of Dominica (population 72,000), where Tropical Storm Erika unleashed a catastrophic deluge on August 27 that brought extreme flooding. The storm caused $612.7 million in damage to roads and bridges, $39.5 million in damage to the airport, and an additional $12 million in clean up costs (thanks go to David C. Adams of Thomson Reuters for this info.) Erika's total preliminary price tag of $675 million East Caribbean dollars, which is about $275 million U.S. dollars--not far from Dominica's annual GDP of $500 million. The storm will likely set the island back 20 years in development, Prime Minister Skerrit said. According to EM-DAT, the international disaster database, Dominica's previous most expensive disaster was the $175 million in damage from Hurricane Marilyn of 1995. Erika's death toll of at least 31 makes it the 3rd deadliest disaster in Dominica's history behind the 40 killed in 1979's Hurricane David and the 2,000 people killed in Dominica by The Dominican Republic Hurricane of 1930.


Video 1. Floodwaters rage through a street on Dominica island in the Caribbean on Thursday, August 27, 2015, after Tropical Storm Erika dumped 12+" of rain on the island.

Deadliest weather disaster of August 2015: Asian monsoon floods
The deadliest weather-related disaster of August 2015, according to insurance broker Aon Benfield, was the monsoon flooding during the first week of August that left more than 303 people dead in India, Bangladesh and Pakistan. At least 250,000 homes were damaged or destroyed by floodwaters and landslides in India, and 89,000 homes in Bangladesh.

However, an even deadlier disaster may have been the heat wave and wildfires that beset Central & Southern Europe and the Middle East. At least 109 direct heat deaths occurred in Egypt in August, and hundreds more indirect heat deaths (excess mortality) likely occurred in areas affected by the intense August heat.


Figure 2. A Pakistani army soldier drops a bag of relief food from an army helicopter to flood affected villagers in the Rajanpur district, in Punjab province, on August 6, 2015. A spokesman for Pakistan's National Disaster Management Agency said that 116 people had died and more than 850,000 people had been affected around the country by this year's monsoon floods. Image credit: SS MIRZA/AFP/Getty Images.

Arctic sea ice falls to 4th lowest August extent on record
Arctic sea ice extent during August 2015 was the 4th lowest in the 36-year satellite record, according to the National Snow and Ice Data Center (NSIDC). Sea ice extent likely reached its annual minimum extent on September 11, bottoming out at the 4th lowest extent on record.

Notable global heat and cold marks set for August 2015
Hottest temperature in the Northern Hemisphere: 52.5°C (126.5°F) at Mitribah, Kuwait, August 2
Coldest temperature in the Northern Hemisphere: -42.4°C (-44.3°F) at Geo Summit, Greenland, August 28
Hottest temperature in the Southern Hemisphere: 42.5°C (108.5°F) at Villamontes, Bolivia, August 31
Coldest temperature in the Southern Hemisphere: -82.6°C (-116.7°F) at Concordia, Antarctica, August 27

Major stations that set (not tied) new all-time heat or cold records in August 2015
Charlotte Amalie AP (U.S. Virgin Islands) max. 35.0°C August 1
Nihonmatsu (Japan) max. 38.0°C August 2
Ishikawa  (Japan) max.  37.5°C August 2
Chizu   (Japan) max. 36.9°C August 2
Higashishirakawa (Japan) max. 36.4°C August 3
Osmaniye (Turkey) max. 43.2°C August 3
Baku (Azerbaijan) max. 41.2°C August 4
Salahaddin (Iraq) max. 41.4°C August 4
Nemuro (Japan) max. 33.6°C August 5
Attoko (Japan) max. 34.9  August 5 
Ikeda (Japan) max. 37.1°C August 5
Nukanai (Japan) max. 36.7°C August 5
Kamisatsunai  (Japan) max. 34.6°C August 5
Sarebetsu (Japan) max. 37.1°C August 5
Taiki (Japan) max. 35.8°C August 5
Taneichi (Japan) max. 35.4°C August 5
Wakayanagi (Japan) max. 36.9°C August 5
Senmaya (Japan) max. 36.2°C August 5
Kashimadai (Japan) max. 35.8°C August 5
Esashi (Japan) max. 37.3°C August   5
Yanagawa (Japan) max. 39.7°C August 5
Funahiki (Japan) max. 34.9°C August  5
Ononimachi (Japan) max. 36.0°C August  5
Monte Rosa Obs. (Italy) max. 9.3°C August 5
Mont Blanc Obs. (Italy) max. 6.1°C August 6
Yoneyama (Japan) max. 36.3°C August  6
Shiogama (Japan) max. 35.8  August 6
Otawara  (Japan) max. 36.8  August 6
Ajiro (Japan) max.  36.8°C August 6
Kawamoto (Japan) max. 37.4°C August 6
Oasa (Japan) max. 35.1°C August 6
Chiba (Japan) max. 38.5°C August 7
Genoa (Italy) max. 38.5°C August 7
Albenga (Italy) max. 38.0°C August 7
Capo Mele (Italy) max. 37.0°C August 7
Strasbourg Airport  (France) max. 38.7°C August 7
Mergentheim (Germany) max. 40.2°C August 7
Mannheim (Germany) max. 39.8°C August 7
Lahr (Germany) max. 39.5°C August 7
Frankfurt City (Germany) max. 39.6°C August 7
Berlin Kaniswall (Germany) max. 38.9°C August 7
Ohringen (Germany) max. 38.9°C August 7
Wurzburg (Germany) max. 39.4°C August 7
Gorlitz (Germany) max. 37.9°C August 7
Plauen (Germany) max. 37.8°C August 7
Wasserkuppe (Germany) max. 32.4°C August 7
Usti nad Orlici (Czech Republic) max. 37.4°C August 7
Stara Boleslav (Czech Republic) max. 38.9°C August 7
Paseka (Czech Republic) max. 37.9°C August 7
Dosky (Czech Republic) max. 38.0°C August 7
As (Czech Republic) max. 34.9°C August 7
Harrachov (Czech Republic) max. 33.9°C August 7
Tuhan (Czech Republic) max. 38.6°C August 7
Javornik (Czech Republic) max. 37.5°C August 7
Krasne Udoli (Czech Republic) max. 35.2°C August 7
Rychnov nad Kneznou (Czech Republic) max. 36.8°C August 7
Wroclaw (Poland) max. 38.9  August 8
Prague Karlov (Czech Republic) max. 38.9°C August 8   
Tuhaň (Czech Republic) max. 38.8°C August  8
Pruhonice (Czech Republic) max. 38.7°C August  8
Ceska Lipa (Czech Republic) max. 38.6°C August  8
Javornik (Czech Republic) max. 38.2  August  8
Pribram (Czech Republic) max. 38.1°C August  8
Semcice (Czech Republic) max. 38.1°C August  8
Doksy (Czech Republic) max. 38.0°C August  8
Minsk (Belarus) max. 35.8°C August 8
Kaunas (Lithuania) max. 35.3°C August 8
Bajandaj (Russia) max. 35.8°C August 8
Kurume (Japan) max. 38.5°C August  8
Aso Otohime (Japan) max. 34.6  August 8
Hitoyoshi (Japan) max. 37.8°C August 8
Hong Kong Observatory (Hong Kong,China) max. 36.3°C August 8
Happy Valley (Hong Kong, China) max. 37.9°C August 8, New Territorial record high for Hong Kong
Hong Kong Int. Airport (Hong Kong,China) max. 37.7°C August 9
Trieste Airport (Italy) max. 37.8°C August 9
Brest (Belarus) max. 36.7°C August 9
Wamena (Indonesia) min. 4.5°C August 15
Sisian (Armenia) max. 36.2°C August 16
Vanadzor (Armenia) max. 36.1°C August 16
Ardebil (Iran) max. 40.5°C August 16
Santo Domingo (Dominican Republic) max. 37.2°C August 27
Jerusalen (Colombia) max. 41.0°C August 29



New all-time national and territorial heat records set or tied in 2015
As of September 14, 2015, twelve nations or territories tied or set all-time records for their hottest temperature in recorded history in 2015, and two (Israel and Cyprus) set all-time cold temperature records. For comparison, only two nations or territories set all-time heat records in 2014, and nine did in 2013. The most all-time national heat records held by any year is nineteen in 2010. Most nations do not maintain official databases of extreme temperature records, so the national temperature records reported here are in many cases not official. I use as my source for international weather records researcher Maximiliano Herrera, one of the world's top climatologists, who maintains a comprehensive list of extreme temperature records for every nation in the world on his website. If you reproduce this list of extremes, please cite Maximiliano Herrera as the primary source of the weather records. Wunderground's weather historian Christopher C. Burt maintains a database of these national heat and cold records for 235 nations and territories on wunderground.com's extremes page. Here are the all-time national or territorial heat and cold records set so far in 2015:

Anguilla set its national heat record on September 12, when the mercury hit 33.8°C (92.8°F) at The Valley Airport.
The U.S. Virgin Islands set their national heat record on September 10, when the mercury hit 35.6°C (96°F) at Charlotte Amalie Airport. Note: the unofficial record listed by NOAA for the U.S. Virgin Islands is 99°F at the Charlotte Amalie Airport in 1988, 1994, and 1996. Mr. Herrera has researched the history of temperature measurements in the islands, and found that data taken at this airport was generally reliable after 1998 and before 1972. Between 1972 to 1998, the data was seriously flawed, with minimum temperatures up to 20°F from the real temperature. There is one other reliable station at the St. Croix Airport, with good data back to 1992. The other dozen or so stations in the islands have data of poor quality.
Hong Kong set its national heat record on August 9, when the mercury hit 37.9°C (100.2°F) at Happy Valley.
Germany set a new national heat record of 40.3°C (104.5°F) twice this year: on July 5 and August 7, both at the Kitzingen station in Bavaria.
Vietnam tied its national heat record of 42.7°C (108.9°F) at Con Cuong on May 30.
Palau tied its national heat record of 34.4°C (94.0°F) at Koror Airport on May 14.
Venezuela set a new national heat record of 43.6°C (110.5°F) at Coro on April 29.
Laos tied its national heat record of 42.0°C (107.6°F) at Thakhek on April 20.
Ghana set a new national heat record of 43.3°C (109.9°F) at Navrongo on April 10. This is the third time this year Ghana has tied or set a new all-time heat record.
Cocos Islands (Australian territory) tied their all-time heat record with 32.8°C (91.0°F) on April 8.
Equatorial Guinea set a new national heat record of 35.5°C (95.9°F) at Bata on March 17.
Wallis and Futuna Territory (France) set a new territorial heat record with 35.5°C (95.9°F) on January 19 at Futuna Airport.

Israel set a new national cold record of -14.2°C (6.4°F) at Merom Golan on January 10.
Cyprus set a new national cold record for an inhabited place of -10.7°C (12.7°F) at Prodromos on January 9 (and also a new cold record for an uninhabited place of -12.0°C at the new mountain station of Troodos Square; unofficial readings in the past were as low as -13°C, though).

Special Mentions:
Antarctica set a new heat record for its mainland of 17.5°C (63.5°F) at Esperanza Base on March 24. Previous record: 17.4°C (63.3°F) at Marambio Base, set the previous day. The World Meteorological Organization (WMO) has appointed a committee to study this event and determine if this represents an official record for the continent. Note that this is a record for mainland Antarctica, not a territorial or continental record. The all-time maximum record for the continent and territory of Antarctica is 19.8°C (67.6°F) on January 30, 1982, in Signy Island, South Orkney, an island group located about 450 miles northeast of the tip of the Antarctic Peninsula, the northernmost portion of mainland Antarctica. Geologically, the South Orkney are on the Antarctic plate, and politically, they are part of Antarctica. This record was improperly listed as a territorial record for Antarctica in May's global summary.

Switzerland had its highest reliably measured temperature on record in Geneva on July 7, when the mercury hit 103.5°F (39.7°C). The only higher temperature ever measured in the country was a 106.7°F (41.5°C) reading on August 11, 2003 at Grono. As reported at the Swiss news site swissinfo.ch, this old record was achieved "using an old measurement technique of weather huts, which generally recorded temperatures a few degrees higher than modern instruments." Weather records researcher Maximiliano Herrera agrees that this year's 39.7°C reading in Geneva is the highest reliably measured temperature ever in Switzerland, though the August 11, 2003 temperature at Grono was probably warmer (near 40°C), after correcting for the known problems with the site.

Samoa was originally listed by Mr. Herrera as tying its national heat record with 36.5°C (97.7°F) on January 20 at Asau, but a subsequent review of the record revealed possible issues with the measurement equipment, so this record is dubious.

Kudos also to Mr. Herrera for supplying the data for the "Notable global heat and cold marks set for August 2015" and "Major stations that set (not tied) new all-time heat or cold records in August 2015" sections.

Jeff Masters

Heat Climate Summaries

Gulf of Mexico Distubance--30% Chance to Develop; TD 9 Struggling; 95L May Develop

By: Jeff Masters , 2:35 PM GMT on September 17, 2015

An area of disturbed weather has developed along the boundary of an old front in the Eastern Gulf of Mexico off the coast of Florida, and is bringing heavy rains to portions of the Florida Peninsula, where 2 - 3" of rain are expected over the next few days. The disturbance is under high wind shear of 20 - 30 knots, and it unlikely to develop in the Gulf. Satellite loops on Thursday morning showed little signs of rotation, and only a modest area of heavy thunderstorms. However, the disturbance is moving to the northeast, and will emerge over the waters off the coast of South Carolina by Saturday, when the GFS and European models predict that wind shear may fall to the moderate range, 15 - 20 knots. This drop in shear may be enough to allow some development. None of our three reliable models for predicting tropical cyclone genesis are showing development of a tropical depression, though. In their 8 am EDT Thursday Tropical Weather Outlook, NHC gave the disturbance 2-day and 5-day odds of development of 10% and 30%, respectively.


Figure 1. Latest satellite image of the Gulf of Mexico, courtesy of NOAA.

Tropical Depression Nine no big deal
Tropical Depression Nine continues to chug to the northwest at 6 mph over the open Atlantic, well away from any land areas. Satellite images show that high wind shear has exposed the surface circulation of TD 9 to view, and the storm has lost almost all of its heavy thunderstorms. The long-range fate of TD 9 is complicated to predict, since the storm will interact with Invest 95L to its southeast. In any case, TD 9 is very unlikely to threaten any land areas, and will be of most concern to trans-oceanic sailors and fish.


Figure 2. Latest satellite image of TD 9.

Invest 95L may develop
A tropical wave (Invest 95L) located about 600 miles southwest of the Cape Verde islands on Thursday morning was moving west-northwestwards at about 10 - 15 mph. Satellite images showed little change to the wave on Thursday morning; 95L has pretty of spin, but dry air is keeping heavy thunderstorm activity meager. Conditions are favorable for development, with wind shear a light 5 - 10 knots, ocean temperatures at 28°C (83°F), and only a modest amount of dry air from the Saharan Air Layer lying to the north of the disturbance. Our three reliable models for predicting tropical cyclone genesis, the UKMET, European, and GFS models, forecasted in their 00Z Thursday runs that 95L would develop into a tropical depression by Monday. In their 8 am EDT Thursday Tropical Weather Outlook, NHC gave 95L 2-day and 5-day odds of development of 70% and 80%, respectively. 95L will turn more to the north over the Central Atlantic over the weekend, and it unlikely to ever pose a threat to the Caribbean or North American coast.


Figure 3. Latest satellite image of 95L.

I'll have a new post by noon EDT, when the results of NOAA's monthly report on August global temperatures will be available.

Jeff Masters

Hurricane

TD 9 Forms in Central Atlantic

By: Bob Henson , 7:05 PM GMT on September 16, 2015

The last few days of rare September quietude in the global tropics are coming to an end, with a new tropical depression in the Atlantic and a named tropical storm in the Pacific. Tropical Depression 9, located about 1200 miles east of the Lesser Antilles, is moving slowly toward the north-northwest. Although TD 9 has a closed circulation and a reasonable amount of shower and thunderstorm activity, it remains a weak system, with top sustained winds of only 30 mph. TD 9’s north-northwest motion reflects the increasing southwesterly upper-level flow that will combine with easterly trade winds to put the depression under strengthening wind shear. This shear will dent TD 9’s chances at growth, even as it approaches an area of sea-surface temperatures 2-3°C above average (around 29°C or 84°F). The 0600 GMT runs of the HWRF and GFDL models bring TD 9 up to tropical storm strength for a brief time during the next 24 to 48 hours, but the official NHC forecast keeps TD 9 short of becoming a named storm throughout the next 120 hours. There could be another window for TD 9 to strengthen in the open Atlantic early next week if its circulation survives the trek.


Figure 1. Visible-wavelength image of Invest 95L, collected by the GOES-East floater satellite at 1445 GMT (11:45 am EDT) on Wednesday, September 16. Image credit: NOAA/NESDIS.

Behind TD 9 is Invest 95L, located well southwest of the Cape Verde islands. With its origins further east than TD 9, 95L has a bit more time to potentially develop into a tropical storm before it encounters the wind shear and relatively dry air that’s been dominating the western and central North Atlantic. NHC gives 95L a 70% chance of becoming a tropical cyclone by Friday. Most statistical and dynamical models gradually intensify 95L to tropical-storm strength while bringing it west-northwest to higher latitudes, reducing the odds it will make it anywhere near North America or the Caribbean.

There are no systems of immediate concern for tropical development near the Gulf or Atlantic coast, although a broad area of surface low pressure will combine with some upper-level support and a weak surface boundary to bring heavy rains to much of the Florida peninsula over the next several days. No flash flood watches were in effect on Wednesday morning, but the NOAA Weather Prediction Center is calling for widespread 2-3” amounts over the southern half of Florida. This could be good news for the Everglades region west of Miami, an area in moderate to severe drought that was largely missed by the extensive rains across Florida this summer.

In the Northwest Pacific, Tropical Storm Krovanh is still on track to become a major typhoon over the next several days. Krovanh could affect the very sparsely populated Iwo Jima and nearby islands as it strengthens rapidly; the Joint Typhoon Warning center brings Krovanh to Category 4 strength in the next 48 hours as it begins recurving over warm waters with relatively light wind shear.


Figure 2.. Enhanced infrared MTSAT image of rapidly organizing Tropical Storm Krovanh from 1714 GMT (1:14 pm EDT) on Wednesday, September 16. Image credit: NOAA/NESDIS.


Flash-flood death toll rises in Utah; Henri’s remnants sock Europe
Some of the worst impacts associated with tropical cyclones this year are happening long after the storms dissipate. Moisture from ex-Hurricane Linda was entrained into rich monsoonal flow that swept across the U.S. Southwest on Monday and Tuesday. As an upper-level trough interacted with the moisture, heavy thunderstorms erupted on Monday over far southern Utah, causing two deadly flash floods that killed at least 16 people. Two vehicles were swept away near the town of Hildale (see our blog post from Tuesday), with 12 people killed and one child still missing. The disturbing photo below (Figure 3) shows the ability of floodwaters to wreak destruction. Many people killed in floods die from trauma rather than from drowning, as pointed out in this overview of flood impacts published in the open-access journal PLOS. During flash floods in mountainous areas, the percentage of deaths caused by trauma is especially high.


Figure 3. The twisted wreckage of two vans that were washed away in a flash flood with women and children inside on Monday, September 14, 2015, rests on the bank of Short Creek near Hildale, Utah, on Tuesday, September 15. Image credit: George Frey/Getty Images.

Just to the northwest of Hildale, in Zion National Park, four canyoneers were killed and three others were missing on Wednesday morning after floodwaters coursed through the narrow Keyhole Canyon on Monday. Zion’s slot canyons are notorious for extremely rapid flash flooding, with little or no ability to escape the water. Less than a mile long, Keyhole Canyon is considered a relatively easy trek, although a permit is required. The website canyonyeeringusa.com rates the generalized flash flood risk of Keyhole as “low”, adding “The collection zone is small, and the canyon short. But it does flash big at times, so don't get caught in there!” Rangers warned visitors on Monday morning of probable flash-flood danger, according to a park spokesperson quoted in the Los Angeles Times. After the second of two thunderstorm complexes passed through around 4:30 pm, the flow through the nearby North Fork of the Virgin River rose from 55 to 2630 cubic feet per second in 15 minutes, a level recorded about once every three years.

Monday’s death toll in Utah appears to have been the largest in a local/regional U.S. flash flood episode since June 11, 2010, when at least 20 people were killed by a flash flood that swept through a remote campsite in southwest Arkansas.


Figure 4. WunderMap radar imagery shows intense thunderstorms stretching from western Germany to southern France at 1445 GMT (4:45 pm CEST) on Wednesday, September 16.

The remnants of former Tropical Storm Henri--having traveled thousands of miles across the Atlantic over the past five days--got swept into a strong midlatitude trough that pushed a broken line of powerful thunderstorms into Germany and France on Wednesday evening. The French newspaper Le Monde reported that at least two people in France were killed by high winds in today’s storms, with several other injured. Winds gusted to 75 mph at Lyon’s Bron airport, the highest wind speed on record for that site in September, according to Nick Wiltgen at weather.com.

Bob Henson

Hurricane Flood

Linda’s Moisture Contributes to Heavy Rain, Deadly Flooding in Southwest

By: Bob Henson , 6:32 PM GMT on September 15, 2015

Utah experienced its single deadliest flash flood on record on Monday, and Los Angeles saw one of the wettest September days in its history, as moisture from the remnants of former Category 3 Hurricane Linda was carried into the Southwest. Strong thunderstorms on Monday afternoon sent torrents of water downstream into a crossroads in the steep terrain just northeast of the town of HIldale, at the Utah/Arizona border just south of Zion National Park. Two vehicles carrying 16 people were swept away by water and debris on Monday afternoon. At least 8 of the 16 occupants died, with 3 others rescued; a woman and four children remain missing. Flash floods are a particular risk in this area because of its steep terrain and narrow canyons, which make it hard to judge one’s risk. Floodwaters can pour into areas where little or no rain has fallen. The downpour was focused in and near the cliffs just upstream (north) of Hildale.


Figure 1. National Weather Service NEXRAD radar reflectivity from 2:20 pm MDT Monday, Sept. 14, 2015, shows an intense thunderstorm with very heavy precipitation (bright red) centered in far southeast Washington County, Utah, near the town of Hildale. A flash flood warning was issued at 2:22 pm for the area. Additional heavy rain struck about two hours later. Image credit: NWS and RAL Real-Time Weather Page.


Figure 2. Debris and water cover the ground after a flash flood Monday, Sept. 14, 2015, in Hildale, Utah. Image credit: Mark Lamont, via AP.


The isolated heavy thunderstorms over Utah and Arizona on Monday emerged as a rich stream of Pacific moisture, with some contribution from Linda’s remnants, intersected with a seasonally strong upper-level trough now making its way across the western United States. Atmospheric soundings from Monday show above-average amounts of water vapor, but even higher amounts have been reported this time of year, so the meteorological setup was not particularly extreme. “I don't see the conditions across Utah as being all that unusual,” Jim Steenburgh (University of Utah) told me. “This is a monsoonal pattern producing monsoon convection.  Flash floods are a natural component of the monsoon system and the geology of the Colorado Plateau.”

As is often the case in flash floods, part of the disaster can be attributed to bad meteorological luck--the fact that an intense thunderstorm happened to develop and move slowly through a particular spot prone to flash flooding. Steenburgh analyzed the topography and meteorology involved in this tragedy this morning at his Wasatch Weather Weenies blog. As shown in Figure 1, an intense thunderstorm struck around 2:20 pm MDT; it was followed by a second intense cell that struck the same area around 4:15 pm MDT (see Steenburgh’s blog for a radar loop). “There is a possibility that the two storms provided a one-two blow that resulted in a more substantial flash flood event than if either had occurred in isolation,” noted Steenburgh. In an email, he added that there is some uncertainty over whether or not the fatal accident happened after the first cell or the second.

Forecasters at the Salt Lake City office of the National Weather Service recognized early Monday morning that a moderate risk of flash flooding existed in southern Utah, and that morning’s hazardous weather outlook warned of the potential for locally heavy rainfall, especially across southern Utah. The office issued a flash flood warning at 2:22 pm MDT for southwestern Kane and southeastern Washington counties, including the Hildale area, noting that radar estimates indicated at least 2” of rain had fallen.

New high-resolution models have increased the ability of forecasters to project the evolution of thunderstorms several hours in advance, but the hugely varied terrain of the Southwest, and the resulting complex patchwork of atmospheric conditions, makes it very difficult to give much advance warning of the kind of flood that struck near Hildale. Further north, Salt Lake City was also hammered by fast-developing thunderstorms that struck the University of Utah campus within 15 minutes of their formation. This prompted UU’s Steenburgh to reflect on the challenges of forecasting in his blog on Monday, prior to the Hildale flood: “There is no human or computer-based forecast tool available today that can reliably forecast the development of a storm cell from nothing on such short time scales...Essentially, developing computer models that can provide detailed and reliable forecasts of convective storms at short lead times represents the holy grail of nowcasting. This is an area of active research in the atmospheric sciences and perhaps we will make some inroads in the coming years and decades, if not for storms like the [Salt Lake City storm], perhaps for severe convective phenomena like derechos and supercells.”


Figure 3. Commuter traffic makes its way slowly along Interstate 10 in downtown Los Angeles amid heavy rain on Tuesday morning, Sept. 15, 2015. Image credit: AP Photo/Richard Vogel.

Heavy rain hits coastal Southern California
Hollywood and environs are getting a sneak preview today of what could be a meteorological blockbuster this winter. The feed of moisture that includes Linda’s remnants is combining with upper-level energy from the Western trough to produce unusually heavy rains for so early in the autumn, with widespread 1” to 2” amounts from the Los Angeles area to northern San Diego County. Several highways have been closed, and more than 100 people were evacuated from a flooded assisted-living center in West Hollywood, as reported by KTLA and the Los Angeles Times. Unfortunately, the rains are too far south to help douse the devastating wildfires now unfolding in northern California.

From midnight through 9:47 am PDT Tuesday, downtown Los Angeles racked up 2.39” of rain, making it the second-wettest September day on record. Only six other September days have yielded more than 1” of rain in downtown LA, where records date back to 1877:

3.96” Sept. 25, 1939
2.39” Sept. 15, 2015 (through 9:47 am PDT)
1.95” Sept. 24, 1986
1.74” Sept. 10, 1976
1.62” Sept. 24, 1939
1.58” Sept. 30, 1983
1.39” Sept. 18, 1965

El Niño conditions were in place and intensifying during all of these events except for 1983, just after the “super” El Niño of 1982-83 had wound down. Since El Niño tends to increase the number of hurricanes in the Northeast Pacific, it’s not surprising that several of the above events were associated with decaying tropical cyclones, including Hurricane Newton (1986), Hurricane Kathleen (1976), Tropical Storm Octave (1983), and the memorable cyclone in 1939 that made landfall near Long Beach as a full-fledged tropical storm (1939), producing a two-day total of 5.58” at downtown Los Angeles and a storm total of 11.60” at Mount Wilson. (Thanks to Jon Erdman and Jen Watson of The Weather Channel for data on the September rains.)



Figure 4. The WU tracking map was devoid of tropical storm names at 1:40 pm EDT on Tuesday, September 15, 2015.

Earth was free of named tropical cyclones on Tuesday morning
There were no named tropical storms on the planet on Tuesday morning, the second such period to occur this month after a 54-hour streak last weekend (the longest such streak September since 2009, according to WU contributor Phil Klotzbach at Colorado State University). The tropics aren’t completely tranquil, though, as several systems are being monitored for potential development.


Figure 5. An infrared image from Meteosat-9 shows Invest 95L (far left) and Invest 93L (center) at 1500 GMT (11:00 am EDT) on Tuesday, September 15, 2015. Image credit: EUMETSAT and NHC.

Invest 95L is the healthiest of the Atlantic waves, with a large area of showers and thunderstorms gradually consolidating south of the Cape Verde islands. Toward the central Atlantic, Invest 93L enlarged substantially overnight, although its convection is somewhat scattered. The National Hurricane Center gives both 95L and 93L a 60% chance of development by Thursday. Models generally support the idea of both 95L and 93L becoming tropical storms later this week. However, as upper-level troughs are now beginning to dig further southward toward the subtropical Atlantic, both systems are likely to recurve long before they have a chance to threaten the Caribbean or North America. The center of Invest 94L has now moved into Mexico near Tampico, although there remains extensive thunderstorm activity to its east under a region of fairly high wind shear (greater than 20 mph). In the Northeast Pacific, Invest 90E should spin harmlessly in open water, with NHC giving it only a 10% chance of development in the next five days.

The one system on Earth now showing potential to become a major tropical cyclone is Tropical Storm Twenty, whose winds reached minimal tropical-storm strength at 1200 GMT Tuesday. The Joint Typhoon Warning Center projects TS 20 to strengthen into a Category 3 typhoon as it recurves just east of Iwo Jima by Friday.

Bob Henson




Hurricane Flood

Wildfires Rage across California; Tropics Quiet for Now

By: Bob Henson , 5:06 PM GMT on September 14, 2015

The explosive fire behavior that many Californians have been fearing all summer came to fruition over the weekend about 70 miles north of San Francisco, as the Valley Fire metastasized from an estimated 400 acres on Saturday to 50,000 acres on Sunday (see timeline at bottom of this page). The fire roared across the community of Middletown on Saturday night, prompting hasty evacuations and apparently destroying large parts of the town. One death has been confirmed by the California Department of Forestry and Fire Protection, and four firefighters from a helicopter crew were hospitalized with second-degree burns. Officials have had trouble confirming the amount of damage as the fire continued to rage nearby, but the National Interagency Fire Center reported in its daily update on Monday that at least 412 structures had been lost. The fire was zero percent contained, and close to 20,000 people have had to evacuate.

Two other large wildland fires are afflicting central California. The Butte Fire, which has scorched 65,300 acres and destroyed at least 214 structures since Wednesday, is now 25 percent contained, with more than 4500 firefighters on the scene and many structures still threatened. The long-burning River Complex Fire, which has roamed across 76,614 acres of far northern California since July 30, is 50 percent contained.


Figure 1. Firefighters create a firebreak near a home in Middletown, California, early on Sunday, Sept. 13, 2015, just ahead of the fast-growing Valley Fire. Image credit: AP Photo/Elaine Thompson.


Figure 2. A kitchen stove sits among the remains of a home on Sunday, Sept. 13, 2015, destroyed by the Butte Fire near Mokelumne Hill, California. Image credit: AP Photo/Rich Pedroncelli.


Figure 3. The infrared signal from the Valley Fire was brighter and larger than Reno, NV, on this image collected early Sunday morning, September 13, 2015, by NASA’s Visible Infrared Imaging Radiometer Suite (VIIRS). Image credit: NWS/Sacramento.


As discussed in this blog a couple of weeks ago, September and October are often the worst months for wildfire in California. The region’s Mediterranean climate leaves it high and dry during summer, so the impact of any drought during the previous winter’s wet season becomes exacerbated by the heat of summer and by the strong winds brought by autumn frontal systems and offshore Santa Ana winds. California is in the midst of a four-year drought on par with anything in the century-plus precipitation record, and state temperatures this year are the warmest on record by far. A new climate.gov analysis by Tom Di Liberto illustrates how tough it will be for California to dig itself out of its multiyear precipitation deficit: every region in California would need record-smashing rainfall this winter in order to bring the five-year totals (2011-12 through 2015-16) merely up to average.

Strong El Niños often bring wet conditions to Southern California, and the intensity of the emerging El Niño event may be enough to extend those above-average rainfalls into the central part of the state, as noted by the NOAA Drought Task Force in a report last month. However, even unusually heavy precipitation may not yield an above-average snowpack in the Sierra Nevada that could help boost water supplies next summer. Snowpack will depend hugely on how cold it is when the biggest storms hit the Sierra, and temperatures are at record warmth both globally and regionally.

Did pyrocumulus play a role?
I asked Daniel Swain, a Stanford University doctoral student and author of the excellent California Weather Blog, to weigh in on the situation. He responded late Sunday night with some clues as to what might have made the Valley Fire behave so explosively.

“It has been really disconcerting to watch this event to watch unfold over a little more than 24 hours. It became pretty clear last night that a true firestorm was underway--50,000+ acres in less than 24 hours and 40,000+ acres in less than 12 hours! What's amazing is that weather conditions were not particularly severe from a fire danger perspective. While there were some gusty winds and warm temperatures, that's not at all unusual for that part of the world. One strange thing did happen, though: a mid-evening ‘heat burst’/gusty wind event seems to have occurred across the North Bay and Lake County area yesterday, possible due to downdrafts from very weak mid-level convective clouds in the area. I've been sent a couple of photographs that suggest that the pyrocumulus cloud from the fire itself may have played a role in this strange event (which I followed with some of the wunderground PWSs, actually!), which would not be that surprising given the magnitude of the fire event. Still, the fact that the fire spread as fast and as far as it did given ambient weather conditions is nothing short of extraordinary.”

Pyrocumulus are the bubbling, cumuliform clouds that often form above large, intense wildland fires. The most spectacular pyrocumulus are sometimes called pyrocumulonimbus for their close similarity to cumulinumbus clouds, sometimes including lightning and anvil-shaped cirrus clouds. Pyrocumulonimbus can even inject aerosols into the stratosphere, according to NASA expert Michael Fromm and colleagues in this open-access article published in 2010 by the Bulletin of the American Meteorological Society. A NASA Earth Observatory article documents spectacular pyrocumulus captured in July 2014 by NASA’s Terra and Aqua satellites during California wildfires.


Figure 4. This view of a developing pyrocumulus cloud above the Oregon Gulch fire, a part of the Beaver Complex fire, was taken from an Oregon Air National Guard F-15C on July 31, 2014, at 8:20 pm PDT. Image credit: James Haseltine, via NASA Earth Observatory.

The role of drought and heat
In his email, Swain also stressed the preconditioning role of this year’s unprecedented combination of drought and heat:

“in some ways, this fire is a realization of widespread fears that California's worst drought on record had created the potential for truly extreme fire behavior this summer and fall. CALFIRE, the state agency tasked with fighting wildfires in California, has been emphatically and explicitly stating that the kinds of extreme fire behavior being observed on the Valley Fire (and other California fires this year) is not something that has been previously observed, and can be attributed directly to the severity of the ongoing, multi-year drought. This kind of on-the-ground assessment is consistent with a number of recent studies suggesting that the observed combination of extremely low precipitation and record-high temperatures is unprecedented in modern California. It's also a very sobering reminder that while many of the impacts of a severe drought are not as conspicuous as those during a more acute meteorological disaster--like a flood or a tornado--sometimes they can be truly and immediately devastating.

As for the week ahead, Swain’s outlook isn’t exactly optimistic:

“The Valley Fire still has zero containment, and is still spreading quickly. Clouds clear tomorrow and winds will start to pick up Tuesday in advance of that weak trough. I'm a bit worried about these pre-frontal winds (could hit 30-40 mph in the fire area), even though the trough itself may drop some light showers in the region. Does look warmer and drier once again after that, so it would be a temporary reprieve at best. Meantime, it seems that Linda's remnants will bring some rain to Southern California early this week (though the models seem to be all over the map with location/amount). If the higher end totals pan out, it'll put a temporary damper on fire season south of Santa Barbara (for perhaps a week or so), but historically that amount of rainfall does very little to mitigate the coming Santa Ana season, which is when most of SoCal's major fires occur.”

A rare September weekend: No tropical cyclones on Earth
We’re just past the climatological peak of the Atlantic hurricane season, and close to the peaks of North Atlantic hurricane and typhoon production as well. Yet for most of this weekend, we had no officially classified tropical cyclones anywhere on the planet. The disturbance shown just east of Vietnam in Figure 5 evolved into short-lived, minimal-strength Tropical Storm Vamco, which was bringing heavy rains early Tuesday local time as it approached the central Vietnam coast (see Figure 6). Varco’s formation ended a 54-hour streak with no tropical cyclones on Earth, the longest such streak to occur in any September since 2009, according to WU blogger Phil Klotzbach (Colorado State University).


Figure 5. At 1400 GMT (10:00 am EDT) on Sunday, September 13, 2015, there were no tropical cyclones anywhere on the planet. The disturbance shown east of Vietnam later became Tropical Storm Vamco. Image credit: Brian McNoldy, University of Miami/RSMAS.


Figure 5. Tropical Storm Vamco (purple blob at center) was moving onto the coast of Vietnam at 1611 GMT (12:11 pm EDT) on Monday, September 14.


Figure 7. This METEOSAT-9 satellite image, collected over the eastern tropical Pacific at 1500 GMT on Monday, September 14, shows tiny Invest 93L (left) and much larger Invest 95L (right). Image credit: NOAA/NHC.

Once Vamco is officially declassified, we may get a second global break from tropical cyclone activity before the next Atlantic system spins up. The most likely candidate is Invest 93L, located several hundred miles west-southwest of the Cape Verde islands at midday Monday. The National Hurricane Center gives 80% odds that this system will become a tropical cyclone by Wednesday. Models are in fairly close agreement that this system will develop into Tropical Storm Ida by midweek, but they also agree it should be recurving sharply by that point, posing no threat to North America or the Caribbean. A much larger tropical wave closer to the African coast, newly designated Invest 95L, is worth watching for potential development later this week. NHC gives this wave 40% odds of becoming a tropical cyclone by Saturday as it enters the central tropical Atlantic. Invest 94L, centered just east of Tampico, Mexico, is associated with a large area of showers and thunderstorms extending into the central Gulf of Mexico at the tail end of a decaying cool front. This system has a chance of developing into a short-lived tropical cyclone over the next several days (NHC gives it 30% odds over the next five days). It would most likely end up tracking westward into Mexico, although its slow development and weak steering currents add some uncertainty to the long-term outlook.

Bob Henson





Video 1. This heart-stopping video was taken by residents evacuating the Anderson Springs area, about five miles northwest of Middletown, California, at 8:30 pm Saturday, September 12, as the Valley Fire roared into the area. Image credit: mulletFive.

Fire Hurricane

Disturbances 93L and 94L Little Threat; All-Time Record Heat in the Caribbean

By: JeffMasters, 3:41 PM GMT on September 13, 2015

An area of disturbed weather has developed along the boundary of a stalled cold front in the Western Gulf of Mexico's Bay of Campeche, and was designated Invest 94L by NHC on Sunday afternoon. Satellite loops show that 94L has a some respectable rotation and a moderate-sized region of heavy thunderstorms, but this activity was not well-organized. Long-range radar out of Brownsville, Texas showed heavy rain from 94L was affecting the Mexican coast, about 100 - 200 miles south of the Texas border. Wind shear was high, near 30 knots, and the 8 am EDT Sunday run of the SHIPS model predicted that wind shear would remain high, 20 - 30 knots, through Tuesday. These are marginal conditions for development, even though ocean temperatures are very warm--near 30°C (86°F). None of our reliable models for tropical cyclone genesis develop 94L, and they show little movement of the disturbance through Tuesday. In their 2 pm EDT Sunday Tropical Weather Outlook, NHC gave the wave 2-day and 5-day odds of development of 10% and 20%, respectively. The Hurricane Hunters are on call to investigate 94L on Monday, if needed.


Figure 1. Latest satellite image of 94L.

Invest 93L in the Central Atlantic may develop
A tropical wave located a few hundred miles southwest of the Cape Verde islands on Sunday morning was moving west to west-northwestwards at about 15 mph. The wave showed a modest increase in its heavy thunderstorm activity overnight, and was designated Invest 93L by NHC on Sunday morning. Conditions are favorable for development, with wind shear a moderate 10 - 20 knots, ocean temperatures at 28°C (83°F), and only a modest amount of dry air from the Saharan Air Layer lying to the north of the disturbance. The 8 am EDT Sunday run of the SHIPS model predicted that the wind shear over 93L through Thursday would be light to moderate, 5 - 15 knots, ocean temperatures would remain near 28°, and the atmosphere would remain relatively moist. Two of our three models for predicting tropical cyclone genesis, the UKMET and GFS models, forecasted in their 00Z Sunday runs that the wave would develop into a tropical depression midway between the Lesser Antilles Islands and Africa by Wednesday. In their 2 pm EDT Sunday Tropical Weather Outlook, NHC gave the wave 2-day and 5-day odds of development of 70% and 90%, respectively. It appears likely that this wave will curve to the north well before it can affect the Lesser Antilles Islands. The next name on the 2015 Atlantic list is "Ida".


Figure 2. Latest satellite image of 93L.

Elsewhere in the Atlantic: more fish storms
NHC is mentioning two other areas of interest in their Tropical Weather Outlook: an area of disturbed weather in the Central Atlantic about about 975 miles southwest of the Azores, far from any land areas, is being given 2-day and 5-day odds of development of 0%. A tropical wave emerged from the coast of Africa on Sunday. All three of our reliable models for predicting tropical cyclone genesis (UKMET, European, and GFS), in their 00Z Sunday runs, predicted that this wave would develop into a tropical depression midway between the Lesser Antilles Islands and Africa by Thursday. In their 2 pm EDT Sunday Tropical Weather Outlook, NHC gave the wave 2-day and 5-day odds of development of 0% and 20%, respectively. This wave will likely follow a path similar to 93L, turning northwards well before reaching the Lesser Antilles Islands. That is likely to be a common fate of tropical waves emerging from the coast of Africa during the remainder of September; we now have an active jet stream across the North Atlantic that is bringing frequent strong troughs of low pressure capable of recurving tropical disturbances to the north.

Remains of Grace bringing rain to the Caribbean
The remains of Tropical Storm Grace are bringing a few showers to Hispaniola and surrounding islands, but high wind shear will discourage any development. Grace's remains brought heavy rain and renewed flooding to the island of Dominica on Saturday, where 31 people died in floods due to Tropical Storm Erika in August. Radar-estimated rainfall amounts of up to 6" fell on the island from Grace's remains, according to the Antigua Met Service. Unfortunately, Grace's remains did little to alleviate the drought in Puerto Rico; San Juan picked up just a trace a rain on Saturday, and is still over 10" below the usual 34" of rain that they should have received by this point in the year.

All-time record heat in the Caribbean
Record heat scorched the Caribbean again on Saturday. According to weather records researcher Maximiliano Herrera, an all-time heat record was set on the island of Anguilla in the Lesser Antilles: 33.8°C (92.8°F), besting the record of 33.7°C set just four days previously. The Cuban capital of La Habana (Havana) also recorded its hottest temperature on record and the hottest temperature ever measured in September in Cuba, with 38.2°C (100.8°F) at the Casablanca Observatory. Havana's previous all-time heat record was set just a few months ago, on April 26, 2015: 37.0°C. According to an email I received from Cuban meteorologist Alejandro Adonis Herrera G., one of the instruments at the site recorded 38.1°C, but with maximum thermometer and technical corrections it was decided that the record is 38.2°C.


Figure 3. Temperature trace from the instrument at Havana's Casablanca Observatory on September 12, 2015. The station hit 38.2°C (100.8°F), the hottest temperature ever recorded in Havana. Image credit: Alejandro Adonis Herrera G.

Record heat and drought has been widespread over the Caribbean this summer, with the worst drought conditions occurring over Haiti, Eastern Cuba, Nicaragua, Panama, Colombia, Venezuela, Honduras, and Costa Rica. Reuters reported last month that Cuba began a two-month cloud-seeding campaign in September over the eastern part of the Caribbean island in hopes of easing its worst drought since at least 1901. The atmospheric circulation associated with the strong El Niño event in the Eastern Pacific has brought warm, sinking air and high pressure to the Caribbean, and has contributed to many cities recording their all-time highest temperatures on record. Another big factor in Saturday's record highs, and the record highs all across the Caribbean this year, is the fact that the year-to-date period of 2015 has been the warmest on record for the globe as a whole. Here is Mr. Herrera's list of cities in countries bordering the Caribbean that have set all-time heat records this year:

Cuba
Havana (Cuba), max. 38.1°C, September 12
Cienfuegos (Cuba) max. 37.0°C July 6
Jucaro (Cuba) max. 36.8°C July 10
Jucaro (Cuba) max. 37.0°C July 28
Contramaestre (Cuba) max. 38.2°C July 29
Isabel Rubio Airport (Cuba) max. 36.3°C July 29
Indio Hatuey (Cuba) max. 38.1°C July 30
Holguin (Cuba), max. 38.7°C, April 26
Guaro (Cuba), max. 38.0°C, April 26
Contramaestre (Cuba), max. 37.7°C, April 27
Velasco (Cuba), max. 38.6°C, April 28
Ciego de Avila (Cuba), max. 38.0°C, April 28
Puerto Padre (Cuba), max. 38.4°C, April 29
Punta Lucrecia (Cuba), max. 37.3°C, April 29
Nuevitas (Cuba), max. 38.5°C, April 30

Colombia
Riohacha (Colombia) max. 40.6°C July 13
Cartagena, Colombia, max. 40.4°C, June 24
Santa Marta, Colombia, max, 38.6°C, June 24
Arjona, Colombia, max, 40°C, June 24
Urumitia, Colombia, max, 42.0°C, June 27
Riohacha, Colombia, max, 40.0°C, June 29

Mexico
Merida (Mexico), max. 43.6°C, April 26

Honduras
Tela (Honduras), max. 40.6°C, April 28

Venezuela
Coro (Venezuela), max. 43.6°C, April 29 (New all-time national record high for Venezuela)

Dominican Republic
Santo Domingo (Dominican Republic), 37.2°C, August 27

U.S. Virgin Islands
Charlotte Amalie (U.S. VI), 35.6°C (96°F), September 10 (all time high for the station and the U.S. Virgin Islands)

Jeff Masters

Hurricane Heat

Only a Few Minor Threat Areas in the Tropical Atlantic

By: Jeff Masters , 2:43 PM GMT on September 12, 2015

A tropical wave that moved off the coast of Africa on Thursday was a few hundred miles south of the Cape Verde islands on Saturday morning, and was moving west to west-northwestwards across the Atlantic at about 15 mph. Though the wave does not yet have much spin or heavy thunderstorm activity, conditions are favorable for development, with wind shear a moderate 10 - 20 knots, ocean temperatures at 28°C (83°F), and only a modest amount of dry air from the Saharan Air Layer to the north of the disturbance. One of our three models for predicting tropical cyclone genesis, the UKMET model, forecasted in its 00Z Saturday run that the wave would develop into a tropical depression midway between the Lesser Antilles Islands and Africa by Monday. Many of the 20 members of the GFS ensemble and 50 members of the European ensemble forecast predicted development by Wednesday, though the operational high-resolution versions of these models were lukewarm in their support of development. In their 8 am EDT Saturday Tropical Weather Outlook, NHC gave the wave 2-day and 5-day odds of development of 10% and 50%, respectively. It appears likely that this wave will curve to the north well before it can affect the Lesser Antilles Islands. The next name on the 2015 Atlantic list is "Ida".


Figure 1. MODIS image of the tropical wave south of the Cape Verde islands from NASA's Aqua satellite taken at approximately 8 am EDT Saturday, September 12, 2015. The Cape Verde islands are visible at the upper right. Image credit: NASA.

Gulf of Mexico disturbance bringing heavy rains to Mexico
An area of disturbed weather has formed in the Western Gulf of Mexico's Bay of Campeche in association with a cold front that pushed south of Texas and has stalled over Mexico and its offshore waters. This disturbance is bringing heavy rains to the coast of Mexico, but none of our reliable models for forecasting tropical cyclone development are predicting that a tropical depression will form in the Gulf over the next five days, due to high wind shear of 20 - 30 knots. The Mexican Weather Service is warning that rainfall amounts of up to 4" may affect portions of Mexico from this disturbance.

Elsewhere in the Atlantic
NHC is mentioning two other areas of interest in their Tropical Weather Outlook, neither of which are a threat to become tropical cyclones that will fact land. The remains of Tropical Storm Grace are bringing a few showers to Puerto Rico and surrounding islands, but high wind shear will discourage any development. An area of disturbed weather in the Central Atlantic about about 1000 miles southwest of the Azores, far from any land areas, is being given 2-day and 5-day odds of development of 10% and 20%, respectively.

Wunderblogger Steve Gregory has an update on the tropics and on the U.S. "Very Active Early Fall Pattern" setting up in his Friday afternoon post.

Have a great weekend!

Jeff Masters

Hurricane

El Niño Heads for Potential Record Strength; Japan Picks up Pieces from Etau’s Rains

By: Bob Henson , 6:31 PM GMT on September 11, 2015

NOAA’s monthly update on El Niño, released on Thursday, held no big surprises: we are on the upswing of one of the strongest El Niño events--very possibly the strongest--of the past 65 years of recordkeeping. As of last week (see PDF), sea-surface temperatures across a key part of the eastern tropical Pacific called Niño3.4 were running 2.1°C above the long-term average for this time of year.


Figure 1. Anomalies (departures from average for this time of year) in sea-surface temperature across the northern and eastern Pacific show the distinct band of warmth in the eastern equatorial Pacific characteristic of El Niño, as well as several other large areas of unusual warmth over the Northeast Pacific Ocean. An excellent article in BayNature explains the persistent “Blob” in the Northeast Pacific and how it might intersect with El Niño in the coming winter. Image credit: Levi Cowan, tropicaltidbits.com.


Every El Niño is different, but the strongest events have some very distinct characteristics. Now that the atmosphere and ocean are in the mutually reinforcing pattern typical of strong El Niños, the course of the next few months is relatively predictable. Niño3.4 anomalies (departures from seasonal average) should continue to rise until peaking sometime around December or January, then subside early in 2016. (In its monthly update, NOAA gives 95% odds that El Niño will continue through the northern winter of 2015-16.) As evident in Figure 1, the odds of neutral conditions will rise dramatically toward spring, but this could represent the beginning of a transition toward La Niña. As the ocean rebounds from strong El Niño conditions, La Niña--a cooling of the eastern tropical Pacific--often, but not always, follows. (See the historical ENSO database for examples.) Since we’re now in the second winter of El Niño conditions (albeit borderline conditions in 2014-15), it’s very unlikely that we’ll see El Niño continue past next spring. I would expect to see gradually rising odds of La Niña in upcoming forecasts as they extend further into 2016. If a La Niña were to develop by mid-year, it would favor a more active Atlantic hurricane season than usual in 2016.


Figure 2. Probabilities of El Niño (red bars), neutral (olive bars), or La Niña (blue bars) conditions for each three-month period from August-October 2015 to April-June 2016, based on a forecaster-consensus outlook produced by NOAA’s Climate Prediction Center and the International Research Institute for Climate and Society. The thin red, olive, and blue lines show the long-term climatological likelihood of El Niño, neutral, or La Niña conditions for each period. Image credit: IRI.


A surge in El Niño strength this month?
In his WU blog, Steve Gregory observed earlier this week that temperatures in the Niño3.4 region appear to have risen by 0.3°C over a period of a week, with the rise not yet fully reflected in NOAA’s weekly El Niño updates (issued each Monday). Steve points out that the Niño3.4 values can vary quite a bit from one week to the next, and NOAA forecasters caution us not to obsess about minor week-to-week changes. That said, it’s worth noting that a weekly change of 0.3°C would fall in the top 5-10% of weekly changes observed from 1990 to mid-2015. If sustained, such a rise would also push the current El Niño event closer to record values.

NOAA’s weekly Niño3.4 values are based on a series of short-term analyses of sea-surface temperature called OISST (optimum interpolation SST). The OISST values include satellite-based measurements that can introduce biases when folded in with older data. To produce one-month and three-month statistics for the Niño3.4 area, NOAA uses a separate data set called the Extended Reconstructed Sea Surface Temperature (ERSST) to rank and classify El Niño events on a monthly and trimonthly basis. This monthly dataset goes back to 1854 and uses statistical techniques to fill in data gaps. The most recent three-month values, called the Oceanic Niño Index, were at 1.2°C above the long-term average for June through August. This is slightly below the JJA value of +1.4 observed during the pacesetting El Niño event of 1982-83. However, the 2015-16 event may now be overtaking 1982-83 in terms of its current strength, an outcome suggested by a range of international computer models (see Figure 3 below).

For more on the implications of El Niño for this winter, see our blog posts on the typical impacts for the U.S. in general and what might happen in the Northeast in particular. Jeff Masters will have a forthcoming post on the potential impacts beyond U.S. borders.


Figure 3. Forecasts by a suite of international computer models tracked by Australia’s Bureau of Meteorology have gotten progressively stronger on the 2015-16 El Niño. For the above outlooks, issued in August and valid in November, the model average (shown in the bottom bar) indicates a Niño3.4 anomaly (departure from the seasonal average) of just above 2.8°C for the month as a whole. If these model runs through winter 2015-16 were to prove accurate, the current El Niño would be the strongest in records going back to 1950. The red and blue shading denotes values above or below 0.8°C, which represent the threshold for El Niño and La Niña, respectively, as used by Australian forecasters. NOAA uses 0.5°C as the threshold, since lesser values can still produce U.S. impacts. More information on each models can be found here. Image credit: BOM.


Japan still recovering from floods, landslides associated with Tropical Storm Etao
Damage continues to mount in central Japan as a result of a persistent band of heavy rain that caused landslides and flooding over the area. The rainband formed on the southeast flank of Tropical Storm Etao as the storm moved northward across the island of Honshu, as the southerly inflow encountered Honshu’s high mountains. The city of Ikari recorded 21.69" (551 mm) of rain in just 24 hours, and the popular destination of Nikko received 26.30" (668 mm) from Sunday into Thursday (thanks go to Maximiliano Herrera for the Ikari rainfall info.) The 24-hour total at Ikari was larger than the city’s previous highest 48-hour total in more than 35 years of recordkeeping. The prolonged rains led to the collapse of a flood berm and the inundation of several areas, including parts of the Tokyo suburb of Joso (population 60,000). At least 3 people are dead and 23 missing, and at least 99 landslides have been reported. Nick Wiltgen at weather.com has much more on the flooding from Etao.


Figure 4. Local residents wait to be rescued on the roof of their home in a flooded area in Joso, Ibaraki Prefecture, on September 10, 2015. The Japanese city about 30 miles (50 km) northeast of Tokyo was flooded when Kinugawa river burst its banks, destroying homes and cars as desperate residents waited for help, and as thousands of people were ordered to evacuate. Image credit: Jiji Press/AFP/Getty Images.


Japan’s destructive rains from Etao may been influenced by the presence of weakening Tropical Storm Kilo to the southeast (see Figure 5). Although Kilo had weakened greatly over the last several days, it still had a large circulation and moisture envelope, and some of that moisture could have been ingested by the rainband located between the two storms. Along these lines, a recent open-access paper in the journal Advances in Meteorology documents the enhancement of a rainband in eastern China associated with Typhoon Fitow in early October 2013. Modeling of the event with and without the presence of Typhoon Danas, located well to the east of Fitow, suggests that moisture from Danas more than doubled the amount of rainfall produced in northern Zhejiang province, from about 220 mm (8.66”) in the non-Danas experiment to the 500-plus mm (more than 19 inches) that was actually observed as well as produced in the model when Danas was included. It’s also possible that the Fujiwhara effect, where two cyclones influence each other’s motion, contributed to Etau’s slowdown in forward speed, which also enhanced rainfall. (Thanks to Naoko Kitabatake, Japan Meteorological Agency, for pointing out the potential interactions between Kilo and Etau.)


Figure 5. Using imagery from Japan’s Himiwari-8 satellite with RealEarth software, this image shows Tropical Storm Etao northwest of Japan; the much larger circulation of Tropical Storm Kilo well to the east; and the intense rainband over eastern Honshu island (center). Image credit: UW-Madison CIMMS.

Elsewhere in the tropics
The Pacific is enjoying a rare moment of quiet in the tropical cyclone realm: both Kilo and Etau have expired as tropical cyclones, according to the Joint Typhoon Warning Center. The only other system of current interest is Invest 99E, which should remain weak as it spins well south of Mexico. The Atlantic is also relatively quiet, with Tropical Storm Henri zipping northeastward with top sustained winds of just 40 mph. Henri may nick southeast Newfoundland on Saturday as a weak post-tropical storm. The National Hurricane Center is tracking two areas with minimal odds of development--one near the northern Lesser Antilles and the other well southwest of the Azores. A wave that recently came off Africa is not expected to evolve significantly over the weekend, although NHC gives it 50-50 odds of developing into a tropical cyclone between Sunday and Wednesday. This system is worth monitoring later next week as it moves into the central tropical Atlantic.

Have a fantastic weekend, everyone--and happy birthday, Jeff Masters!

Bob Henson

Hurricane El Niño

Henri Forms; a New African Wave is Worth Watching; Etau Deluges Japan

By: Jeff Masters , 4:03 PM GMT on September 10, 2015

Tropical Storm Henri got its name on Wednesday evening in the waters a few hundred miles east of Bermuda, but appears destined to be short-lived and quickly forgotten. Henri is under moderate wind shear of 15 - 20 knots, which is inhibiting development, but ocean waters are warm, near 28°C (82°F). The 8 am EDT Thursday run of the SHIPS model predicted that Thursday night through Friday night, Herni should find moderate wind shear of 5 - 15 knots and a moister atmosphere, which should allow it to intensify into a strong tropical storm. By Saturday morning, Henri will have crossed over the warm waters of the Gulf Stream into very cold waters of 17°C (63°F), which should cause a rapid transition to an extratropical storm. Henri will pass close to southeast Newfoundland, Canada on Saturday morning. Henri's formation date of September 9 comes two weeks earlier than the usual September 24 formation date for the Atlantic's eighth named storm of the year, and matches the total number of named storms that occurred during the entire year the last time we had a strong El Niño event--in 1997. The Atlantic has seen close to average levels of activity this year: 8 named storms, 2 hurricanes, and 1 major hurricane; a typical season sees 6 named storms, 2 hurricanes, and 1 major hurricane by this point in the season. However, this year's storms have been weaker and shorter-lived than usual; our Accumulated Cyclone Energy (ACE) index (25) is about half of average (50.) The official halfway point of the Atlantic hurricane season is September 11, so we are halfway home!


Figure 1. Latest satellite image of Henri.

New African tropical wave worth watching
A tropical wave moving off the coast of Africa on Thursday has the potential to develop into a tropical depression early next week as it moves westwards across the Atlantic at about 15 mph. Though the wave does not yet have much spin or heavy thunderstorm activity, conditions are favorable for development, with wind shear a moderate 10 - 20 knots, ocean temperatures at 27.5 - 28.5°C (82 - 84°F), and only a modest amount of dry air from the Saharan Air Layer to the north of the disturbance. One of our three models for predicting tropical cyclone genesis, the UKMET model, forecasted in its 00Z Thursday run that the wave would develop into a tropical depression midway between the Lesser Antilles Islands and Africa by Sunday. Many of the 20 members of the GFS ensemble forecast also predicted development, though the operational high-resolution version of the GFS model did not. In their 8 am EDT Thursday Tropical Weather Outlook, NHC gave the wave 2-day and 5-day odds of development of 0% and 20%, respectively. This wave looks less likely to affect the Lesser Antilles Islands than the waves that spawned Grace, Erika, and Danny, but it is too early to be confident of this.

Gulf of Mexico disturbance next week
An area of disturbed weather is expected to form in the Western Gulf of Mexico's Bay of Campeche on Sunday or Monday next week. This disturbance will be capable of developing into a tropical depression, and could bring heavy rains to the coast of Mexico south of Texas early next week.


Figure 2. Tropical Storm Kilo as seen by the MODIS instrument on the Aqua satellite at 02:50 UTC September 10, 2015. At the time, Kilo had top winds of 65 mph. Image credit: NASA.

Kilo and Linda continue to churn the Pacific
In the Eastern Pacific off the coast of Mexico's Baja Peninsula, Tropical Storm Linda quickly weakened to a minimal-strength tropical storm with 40 mph winds at 11 am EDT Thursday. A northeasterly flow of moisture along the east side of Linda continues to stream into Northwest Mexico and the Southwest U.S., and will contribute to numerous thunderstorms with heavy rain over the next two days. Flash flood watches are posted for Southwest California for the regions just inland from San Diego to Los Angeles. Linda is expected to be dead by Friday. Long-lived Tropical Storm Kilo has finally weakened below hurricane strength, after being a Category 1 or stronger storm for thirteen days. Kilo became a tropical depression on August 20, and is now entering its 22nd day as a tropical cyclone. Kilo will move on a northerly path that will take it into the cold waters between Russia and Japan on Friday night, when it will finally die after 23 - 24 days as a tropical cyclone. According to the Hurricane FAQ, this will make Kilo one of the top-ten longest-lived tropical cyclones on record. In the Central Pacific waters about 300 miles north of Honolulu, Hawaii, Tropical Storm Jimena finally died on Thursday, after fifteen days as a tropical cyclone.


Video 1. A house floats away and a rooftop helicopter rescues occur in the floodwaters spawned by Japan's Tropical Storm Etau. Thanks go to wunderground member Xandra for posting this video in my blog comments.

Tropical Storm Etau deluges Japan
Tropical Storm Etau hit Japan just after 10 a.m. on Sept. 9 on the Chita Peninsula, Aichi Prefecture. A band of heavy rain set up over the northern Tokyo metropolitan area, bringing extreme rainfall and catastrophic flooding. The city of Ikari recorded 21.69" (551 mm) of rain in just 24 hours, and Nikko has received 26.30" (668 mm) since Sunday (thanks go to Maximiliano Herrera for the Ikari rainfall info.) For more details, see the news story by TWC's Nick Wiltgen.

The challenges NHC faced on predicting the path and intensity of Tropical Storm Erika are discussed by James Franklin, Branch Chief of the Hurricane Specialist Unit, in a September 9 blog post, After Further Review: Tropical Storm Erika.

Jeff Masters

Hurricane

El Niño Expected to Increase Nuisance Coastal Flooding in U.S.

By: Jeff Masters , 7:03 PM GMT on September 09, 2015

In the waters of the Eastern Pacific, strong westerly winds have pushed a massive amount of warm water against the coasts of the Americas, resulting in one of the strongest El Niño events ever observed. Not only does El Niño impact atmospheric patterns, changing storm tracks and suppressing Atlantic hurricane frequency, it also typically resulting in an increase in coastal “nuisance” flooding at high tide along the U.S. West Coast and mid-Atlantic coasts. Nuisance flooding is expensive, causing frequent road closures, overwhelmed storm water systems, and damage to infrastructure. According to a September 9 press release from NOAA, some cities along the mid-Atlantic coast can expect record amounts of “nuisance” flooding at high tide during the coming winter—at Sandy Hook, NJ, Lewes DE, Washington D.C. and Norfolk, VA.


Figure 1. Nuisance street flooding in Norfolk, Virginia on October 9, 2013, during passage of a front at high tide. In the background: on the right side is a church built in 1902 and now for sale largely due to frequent flooding, and in the middle behind the trees is the Chrysler Museum of Art that just completed renovation that include improvements to reduce the potential damage from flooding. Image credit: Tal Ezer, Old Dominion University.

How El Niño events cause more coastal flooding
Along the U.S. West Coast, El Niño wind patterns drive ocean currents that pile up water along the coast, raising sea level for many months. Recent satellite data show that ocean levels are elevated by 7 - 18 cm (3 - 7”) along the coast of North America, from California to Mexico. Along the mid‐Atlantic coast, atmospheric patterns during El Niño typically favor more and stronger winter storms along the coast that drive a higher frequency of storm surges. Both conditions have historically led to flooding during periods of seasonally high tides in the non-summer months. Along the U.S. West Coast, the nuisance flooding resulting from the El Niño-driven boost to the base water level is not a big deal during high tide--if it's a nice sunny day. However, the higher base sea level means that if a whopper storm does hit the coast during El Niño, the resulting storm surge could potentially do a lot more damage. Along the mid‐Atlantic coast, the storm surges from El Niño-related extratropical storms will not be riding up on top of an elevated base sea level like occurs on the West Coast.


Figure 2. Street flooding in Norfolk, Virginia has increased dramatically in recent years, largely due to global-warming induced sea level rise. However, part of the steep increase in Norfolk's flooding events may be due to a slowdown of the Atlantic Meridional Overturning Circulation (AMOC) and its upper branch, the Gulf Stream. See the 2013 paper Ezer et al., Gulf Stream's induced sea level rise and variability along the U.S. mid-Atlantic coast. The top years for flooding in Norfolk, 1998 and 2009, both featured El Niño events, and a series of significant coastal storms (twin major Nor'easters in 1998, and the Veteran's Day Nor'easter of 2009.) Norfolk experienced eight nuisance flood days during the 2014 meteorological year (May 2014 through April 2015), and the new NOAA report predicts that the city may experience 18 days in meteorological year 2015 (May 2015 - April 2016), due to El Niño—125 percent above average. Image credit: Larry Atkinson.

“We know that nuisance flooding is happening more often because of rising sea levels, but it is important to recognize that weather and ocean patterns brought on by El Niño can compound this trend,” said co-author of the report, William Sweet. “By using the historic data that NOAA has collected from tide gauges for more than 50 years, we can better understand and anticipate how the weather patterns may affect nuisance flooding in these communities.”

Links
AP news story on the report by Seth Borenstein
Sea Level Rise Making Floods Routine for Coastal Cities, October 2014 story from Climate Central

Today (September 9) is the 50th anniversary of Category 3 Hurricane Betsy hitting Louisiana. Storm Surge expert Hal Needham has a blog post analyzing Betsy's storm surge.

Wunderblogger Steve Gregory has a new Wednesday afternoon post, California Heat Wave While Much Cooler Temps overspread the East.

Jeff Masters

Flood Sea level rise

Grace Dissipates; TD 8 Forms South of Newfoundland

By: Jeff Masters , 3:27 PM GMT on September 09, 2015

Tropical Depression Eight spun into life on Wednesday morning in the waters a few hundred miles east-southeast of Bermuda, and appears poised to become Tropical Storm Henri by Thursday. TD 8 is under high wind shear of 20 knots, which is inhibiting development, but ocean waters are warm, near 28.5°C (83°F). The 8 am EDT Wednesday run of the SHIPS model predicted that by Thursday, TD 8 should find moderate wind shear of 5 - 15 knots and a much moister atmosphere, which should allow it to become a tropical storm. By Friday afternoon, TD 8 will move northwards across the warm waters of the Gulf Stream, and encounter very cold waters near 23°C (73°F), which should cause a rapid transition to an extratropical storm. TD 8 will likely pass over or near southeast Newfoundland, Canada on Saturday morning.


Figure 1. Latest satellite image of TD 8.

Grace dissipates
Tropical Storm Grace finally succumbed to dry air and high wind shear and dissipated on Wednesday morning. The remains of Grace could produce some gusty winds and showers over portions of the Lesser Antilles on Friday.

Gulf of Mexico disturbance next week
An area of disturbed weather is expected to form in the Western Gulf of Mexico's Bay of Campeche on Sunday or Monday next week. This disturbance will be capable of developing into a tropical depression, and could bring heavy rains to the coast of Mexico south of Texas early next week.


Figure 2. Hurricane Linda near peak intensity as seen by the GOES West satellite at 2 pm EDT September 8, 2015. At the time, Linda was a Category 3 storm with 125 mph winds. Image credit: NOAA Viz Lab.

Three tropical cyclones in the Pacific
In the Eastern Pacific off the coast of Mexico's Baja Peninsula, Hurricane Linda put on a spectacular show on Tuesday, peaking as a Category 3 storm with 125 mph winds--the Northeast Pacific's fifth major hurricane of the season. A northeasterly flow of moisture along the east side of Linda is streaming into Northwest Mexico and the Southwest U.S., and will contribute to numerous thunderstorms with heavy rain over the next two days. Flash flood watches are posted for Southwest California for the regions just inland from San Diego to Los Angeles. As of 11 am EDT Wednesday, Linda had weakened to a Category 1 storm with 80 mph winds, and is expected to continue to weaken to tropical depression status by Thursday, well offshore from Mexico. In the Central Pacific waters 320 miles north of Honolulu, Hawaii, Jimena has weakened to a tropical depression with top sustained winds of 35 mph at 11 am EDT Wednesday. Jimena will continue to weaken over the next few days, and will not bring heavy rain to Hawaii. Long-lived Category 1 Typhoon Kilo is now in its 21st day as a tropical cyclone and 12th day at hurricane strength. Kilo is predicted to move on a northerly path that will take it into the cold waters between Russia and Japan on Friday, when it will finally die after 23 - 24 days as a tropical cyclone.

Tropical Storm Etau hit Japan just after 10 a.m. on Sept. 9 on the Chita Peninsula, Aichi Prefecture. A band of heavy rain associated with Etau is hammering the Tokyo metropolitan area. As of 11 am EDT Wednesday, evacuation advisories are currently in effect for about 697,000 people. The vast majority (626,000) are in the city of Kawasaki, just south of Tokyo. According to JMA, the highest 24-hour rainfall total is currently 398 mm (15.67 inches) in Dorobu, part of the city of Nikkō in Tochigi Prefecture. That's the highest 24-hour total ever recorded at that location since observations began there in 1977. The top 72-hour total is 438 mm (17.24 inches) in Okunikkō, which is also part of the city of Nikkō (thanks go to TWC's Nick Wiltgen for this info.)


Weather Underground has opened a new Weather Underground store where you can get your favorite WunderFriend t-shirt or hood. Not sure which style is best? Take this short quiz to see which WunderFriend fit best here.

Today (September 9) is the 50th anniversary of Category 3 Hurricane Betsy hitting Louisiana. Storm Surge expert Hal Needham has a blog post analyzing Betsy's storm surge.

Jeff Masters

Hurricane

Grace on the Decline; 92L Forms near Bermuda

By: Bob Henson , 3:58 PM GMT on September 08, 2015

As we approach the peak of hurricane season, 2015 continues to underwhelm in terms of tropical cyclone intensity across the Atlantic, though we’re a bit ahead of schedule on the number of named storms. From 1966 to 2009, the median date for the seventh named storm was September 16. This year’s #7 system was downgraded to Tropical Depression Grace with the 11 am EDT advisory from the National Hurricane Center. Grace saw a modest flare-up of convection on Monday night, but by Tuesday morning, showers and thunderstorms were again on the wane around Grace’s center, struggling against dry mid-level air and persistent wind shear. At 11 am EDT Tuesday, Grace was located more than 1200 east of the Lesser Antilles, moving west at about 20 mph. Grace’s top sustained winds were down to 35 mph, and with conditions even more hostile down the road, Grace should degenerate into a post-tropical low or a tropical wave by Thursday, if not sooner.


Figure 1. Invest 92L (top) is healthier-looking than Tropical Depression Grace (bottom) in this water-vapor image from the GOES-East satellite, taken at 1445 GMT (10:45 am EDT) on Tuesday, September 8, 2015.

Convection was much more robust on Tuesday morning around Invest 92L, located about 300 miles east-southeast of Bermuda. Sea-surface temperatures throughout the northwest Atlantic north of 20°N are running 1-2°C above normal, which will provide 98L with ample oceanic fuel. Upper-level flow will remain weak above 98L for the next several days. NHC gives 98L a 40% chance of development over the next five days, and statistical models are in league with the HWRF in bringing Invest 92L to tropical storm strength over the next couple of days. By the weekend, 92L could be clipping southeast Newfoundland on a rapidly recurving trajectory.

Another area to watch is the far western Gulf of Mexico, where the tail end of a cool front may intersect with a weak upper-level low slated to drift westward during the week. Long-range forecasts from the GFS and European models continue to suggest that a tropical cyclone might develop in the far western Gulf over the weekend or early next week. Even if no such system develops, large amounts of deep tropical moisture are likely to be steered into the upper Gulf Coast region, possibly dumping heavy rain.

Linda surges to Category 3 strength
Making the most of a favorable environment that won’t last long, Hurricane Linda rapidly intensified to Category 3 strength on Tuesday morning, becoming the fifth major hurricane of 2015 in the Northeast Pacific. Linda’s top sustained winds were 120 mph in the 11 am EDT Tuesday advisory from NHC. Linda’s strength will be no match for the increasingly cool waters and stable air that lie ahead of the hurricane on its northwestward track, which will run parallel to and about 300 miles west of Baja California.


Figure 2. A visible-wavelength image of Hurricane Linda collected by the GOES-West satellite at 1430 GMT (10:30 am EDT) on Tuesday, September 8, 2015. Image credit: NOAA/NESDIS.

Meanwhile, Tropical Storm Jimena continues on a rare track that’s taking it westward across the Pacific several hundred miles north of Hawaii. Jimena’s upper- and lower-level centers of circulation have been hard to reconcile over the last 24 hours, but the storm has hung on in the face of westerly wind shear of more than 25 mph. “This seems to be the season for stubbornly resilient storms,” mused a forecaster at the Central Pacific Hurricane Center in a discussion of Jimena on Monday night. Jimena may survive for several more days before its remnants become absorbed in a midlatitude front.

Etau approaches Japan; Kilo heads for Siberia
Tropical Storm Etau will bring heavy rains and wind to the Japanese island of Honshu, including Tokyo, as it sweeps through on Tuesday night (Wednesday morning local time). More than 120,000 people have been advised to evacuate. Etau should make landfall near the city of Nagoya, more than 100 miles southwest of Tokyo.


Figure 3. The convective core of Tropical Storm Etau was visible on radar southeast of Japan at 0035 JST Wednesday, September 9 (11:35 am EDT Tuesday). Image credit: Japan Meteorological Agency.

In its 11th day as a hurricane-strength system and its 20th day as a tropical cyclone, Typhoon Kilo continues its prolonged traverse of the North Pacific. Kilo was at minimal typhoon strength on Tuesday morning (sustained 1-minute winds of 75 mph) and was moving to the west-northwest at an increasing pace. Kilo may intensify slightly over the next several days before rapidly recurving toward Siberia’s Kamchatka Peninsula as a weakening post-tropical storm by this weekend. Though an impressively long-lived system, Kilo is destined to fall well short of the record 31 days as a tropical cyclone set by Hurricane/Typhoon John in 1994.

Jeff Masters will be back with our next post on Wednesday.

Wunderblogger Steve Gregory has an update on the remarkable new El Niño numbers in his Tuesday afternoon post.

Bob Henson


Figure 4. Long-lived Typhoon Kilo remains an elegantly structured tropical cyclone, as evident in this enhanced infrared MTSAT satellite image from 1401 GMT (10:01 am EDT) on Tuesday, September 8, 2015. Image credit: Japan Meteorological Agency.

Hurricane

Remembering the Labor Day Hurricane of 1935 in the Florida Keys

By: Bob Henson , 5:50 PM GMT on September 07, 2015

As Tropical Storm Grace struggles in the Atlantic (see below), today offers a chance to commemorate the victims of a much more devastating cyclone. Eighty years ago, on this federal holiday that recognizes U.S. workers, a group of World War I veterans toiling to improve life on the Florida Keys lost their lives in one of the great workplace tragedies of U.S. history. The strongest landfalling hurricane on record in the Western Hemisphere brought Category 5 winds and a terrifying storm surge to the upper Florida Keys on the late evening of Monday, September 2, 1935. The compact Labor Day hurricane of 1935 developed very rapidly from a system that was classified as a tropical storm less than two days before landfall in the Keys. Brushing the south end of Andros Island, it headed toward the north coast of Cuba before angling unexpectedly rightward and intensifying with astonishing speed as it approached the Keys, passing over the very warm waters of the Florida Straits. As the hurricane barreled across the Keys on Monday night, local weather observer Ivar Olsen measured 26.35” (892 mb) with a barometer that was later tested and proven reliable at the Weather Bureau. This remains the lowest value ever measured by a ground-based station in a tropical cyclone in the Western Hemisphere. (Dropsondes released by reconaissance aircraft produced sea-level pressure measurements of 882 mb on October 19, 2005, during Hurricane Wilma, and 870 mb on October 12, 1979, during Typhoon Tip). The 1935 hurricane went on to skirt the west coast of the Florida peninsula before accelerating northeastward, reentering the Atlantic off the Virginia coastline and producing rains that topped 16” in Maryland.


Figure 1. Track of the 1935 Labor Day hurricane.


Figure 2. Surface weather analysis from the U.S. Weather Bureau for September 4, 1935, showing the Labor Day hurricane two days after it struck the Keys. NOAA, via Wikipedia.

The storm’s rapid development combined with several other factors to produce the human tragedy that resulted. No satellite monitoring was available in 1935, and ships avoided tropical cyclones for good reason. As a result, forecasters at a brand-new Hurricane Warning Center, established that year in Jacksonville, Florida, by the U.S. Weather Bureau, could only surmise from nearby surface stations how quickly the storm was developing and how its motion was evolving. Persistence forecasting suggested that the storm’s west-southwest motion would take it to the north coast of Cuba, but there was little sign of its approach there on Monday morning. An American “barnstormer” pilot with the Cuba Army Air Corps, Capt. Leonard Povey, volunteered to carry out what is believed to be the first-ever hurricane-hunter flight, approaching the storm on Monday afternoon in an open-cockpit Curtis Hawk II aircraft. Povey found the hurricane further north than expected, and a hurricane warning was issued for the Keys at 4:30 pm, just a few hours before the hurricane struck full force.


Figure 3. Drawings of the Curtis Hawk II aircraft that Capt. Leonard Povey used to investigate the 1935 Labor Day hurricane in the world’s first known “hurricane hunter” flight. Image credit: NOAA Hurricane Research Division.


Figure 4. The rescue train derailed by the 1935 Labor Day hurricane before it had a chance to rescue the hundreds of veterans stationed on the Keys. Image credit: Wikipedia.

The most heartbreaking parts of the saga are vividly told in “Storm of the Century: The Labor Day Hurricane of 1935” (National Geographic, 2002), which I reviewed for Weatherwise magazine. (This interview with author Willie Drye hits many of the main points.) Hundreds of veterans had been deployed to the Keys to build the most difficult sections of the highway that now runs the length of the island chain, from Key West to Miami. Many veterans of World War I had struggled to find work and deal with postwar life, and the Great Depression hit them particularly hard. At the Keys, they were housed in hastily built barracks and tents that stood no chance of surviving a Category 5 hurricane. Superiors recognized the potential for disaster if a hurricane were to strike, but as “Storm of the Century” recounts in agonizing detail, a series of miscues--ranging from slack holiday schedules to telephone miscommunications to obstructions along the railway track to simple inertia--meant that a rescue train ran hours later than it should have. The train ended up pushed off its tracks by the storm; miraculously, everyone on board survived, but the train had not yet reached hundreds of the most vulnerable workers. At least 257 veterans and 228 civilians died in the winds and storm surge of that horrifying evening. (See video at bottom, which includes recent interviews with two survivors.]

How much at risk are the Keys today?
An 80th-anniversary symposium held on September 2 at the Keys History & Discovery Center in Key West looked back at the awful events of 1935 from the perspective of today’s hurricane risk. The presenters included local historian Jerry Wilkinson, who has studied the hurricane for decades and worked to establish permanent individual markers for the lost veterans, and former National Hurricane Center director Max Mayfield, who discussed the current landscape of NWS and NHC hurricane warnings and the continued vulnerability of the Keys. A second night of commemoration will take place Tuesday, September 8, at the Keys History & Discovery Center. Curator Brad Bertelli will join British-based novelist and Florida native Vanessa Lafaye, author of “Under a Dark Summer Sky,” a work of historical fiction set during the 1935 hurricane.

Also participating in the September 2 event was Matt Moreland, who this spring became meteorologist in charge at the Key West NWS office--which began as an observing post in 1870, the same year that the NWS was established. In a phone chat, Moreland emphasized that the placid weather of the Key West location during much of the year is counterbalanced by the location’s risk to hurricane impacts. “Something like the 1935 hurricane still represents our worst-case scenario--a hurricane going from Category 1 to Cat 5 in 36 hours,” said Moreland. “Once you get to Cat 3 or higher, there is a threat of extensive flooding for all of the islands, and portions of the Overseas Highway as well.” On any given day, about 100,000 residents and tourists are strung along the 120-mile stretch of the Keys, which have only one highway escape route. It’s estimated that a full evacuation (including residents, tourists, and those with special needs) would need to begin 84 hours in advance.


Figure 5. A couple walks hand in hand as they brave flood waters several feet deep along South Street in Key West, Florida, after Hurricane Wilma passed through in the early morning hours of October 24, 2005. Along with some wind damage, the majority of the island was indundated. Image credit: Josh Ritchie/Getty Images.

The Keys have had several close calls this century, including 2005’s Hurricane Rita, which was in the process of intensifying to a Cat 3 while crossing over the Florida Straits south of the Keys. “If the track had come 30 or 40 miles further north, the lower Keys would have seen extensive damage,” said Moreland. “That kind of track error is not uncommon at 24 hours out.” Later in 2005, Hurricane Wilma flooded more than 60% of Key West, destroyed more than 10,000 vehicles, and inflicted more than $1 billion in damage across Monroe County (which includes all of the Keys). One of Moreland’s biggest concerns is complacency, along with the high turnover of the workers that keep tourism humming along the Keys. Outreach and decision support are critical parts of the NWS/Key West mission. Moreland and colleagues work year-round to maintain close ties with a wide range of partners, including local, county, and regional emergency managers; federal entities from the Coast Guard to the Navy to the National Park Service; and the Monroe County Tourist Development Council, which provides storm updates with official NWS information to hotels and resorts. According to Moreland, these strong relationships and the office’s teamwork-oriented approach ensure that decision makers in the Keys stay vigilant against the prospect of a 1935-type storm.


Figure 6. At the September 2, 2015, commemoration of the Labor Day 1935 hurricane at the Keys History & Discovery Center: (left to right) NWS/Key West forecaster Bill Cottrill; former NHC director Max Mayfield; NWS/Key West forecaster Krizia Negron; and NWS/Key West meteorologist in charge Matt Moreland. Image credit: Courtesy Matt Moreland.


Figure 7. A visible GOES-East satellite image of highly sheared Tropical Storm Grace, collected at 1545 GMT (11:45 am EDT) on Monday, September 7, 2015. Image credit: NOAA/NESDIS.

Grace under fire; Gulf bears watching later this week
Tropical Storm Grace failed to take advantage of the usual nighttime bump in thunderstorm activity, and it appears that Grace’s window for becoming a stronger system is rapidly closing. Wind shear to Grace’s north is forcing shower and thunderstorm activity toward Grace’s south side, as was the case with Tropical Storm Erika a few days ago. As Grace continues westward through the central Atlantic, with winds of only 45 mph, it will encounter increasing westerly wind shear and relatively dry air. In its 11 am EDT update, NHC projects Grace to be a post-tropical remnant low south of Puerto Rico by Saturday. Dynamical models are in general agreement, save for the suspiciously bullish GFDL model.

A weak upper-level low and surface trough now producing scattered thunderstorms in the eastern Gulf of Mexico will drift slowly westward through the week, perhaps intersecting with the tail end of a cool front in the western Gulf by this weekend. The 0000 GMT Monday run of the European model suggests the possiblity of some hybrid/subtropical development this weekend in the far western Gulf, with very rich moisture surging toward the Texas/Louisiana coast, and the 1200 GMT Monday run of the GFS model shows low surface pressure taking shape in the Bay of Campeche over the weekend. We’ll have plenty of time to watch for this potential development.

In the Northeast Pacific, Hurricane Linda has surged to Category 2 intensity, with top sustained winds of 100 mph. Linda may reach Category 3 strength before a rapid decline begins, as the hurricane’s track takes it toward progressively cooler water and drier air. Dynamical models generally turn Linda westward by the weekend, although some of Linda’s moisture may stream into the southwest United States later this week. Further west, Typhoon Kilo continues its slow weakening and recurvature well east of Hawaii, while newborn Tropical Storm Etau could bring heavy rain to Japan later this week as a weak tropical storm or depression.

Have a great Labor Day, everyone!

Bob Henson


Video 1. This Miami Herald video includes compelling photos from the Labor Day hurricane of 1935, as well as new interviews with Everett Albury and Alma Pinder Dalton, who were 6 and 11 when the hurricane struck. Video credit: Jenny Staletovich/Miami Herald staff. Thanks to wunderground member barbamz for locating this video.

Hurricane

In Eastern Atlantic, Grace Intensifies While Fred Clings to Life

By: Bob Henson , 5:07 PM GMT on September 06, 2015

Tropical Storm Grace became the Atlantic’s seventh named storm of the 2015 tropical season on Saturday. Grace’s arrival keeps this year’s pace of named Atlantic storms close to the long-term average: during the period 1966-2009, the average date of formation for the seventh named storm was September 16. With top sustained winds of 45 mph as of 11:00 am EDT Sunday, Grace was moving just north of due west at about 14 mph through the eastern Atlantic, about 450 miles west-southwest of the Cape Verde islands. Grace took advantage of the typical nighttime surge in tropical cyclone convection to build a north-south swath of heavy thunderstorms around its center. The convection has ebbed somewhat in intensity over the last few hours, but Grace remains quite well structured in visible satellite imagery, though its convective envelope remains elongated.


Figure 1. An infrared view of Tropical Storm Grace (center) and a significant wave moving into the Atlantic from Africa (far right), taken at 1515 GMT (11:15 am EDT) on Sunday, September 6, 2015. Image credit: UW-CIMMS


Over the next couple of days, Grace will move over sea-surface temperatures of 27-28°C (80-82°F), slightly above average for this time of year. Wind shear will be relatively light beneath a weak upper-level ridge. The National Hurricane Center projects Grace to become a strong tropical storm by late Monday, and I’d put at least 50-50 odds on the likelihood of Grace making it to minimal hurricane status by Monday or Tuesday. Later in the week, as Grace moves west of 40°W, the storm will encounter an intensifying belt of southwesterly upper-level winds extending from the Caribbean into the central Atlantic. Vertical wind shear of more than 40 knots will develop, and Grace is likely to decay significantly as the shear disrupts its circulation and injects dry air into its core. NHC projects Grace to be no more than a minimal tropical storm by Thursday, as it approaches the Lesser Antilles.

Grace is the fourth storm this year to develop in the deep tropics of the eastern Atlantic--the Cape Verde development region, which can produce some of the longest-lived and most dangerous hurricanes to affect the United States. Getting so many Cape Verde storms this year is a bit surprising given the hostile conditions engendered by this year’s intensifying El Niño event, which is at record strength for early September. As noted by wunderground member Webberweather53, this is the first time that at least four named systems have developed east of latitude 60°W during a strong El Niño event. El Niño is responsible for hurricane-snuffing wind shear that has been at record levels for most of the summer over the Caribbean and nearby waters. It’s no coincidence that this year’s only two Atlantic hurricanes to date, Danny and Fred, both peaked in strength well east of the Lesser Antilles. Although Danny briefly reached Category 3 strength, the Atlantic has seen a total of only about 78 hours of hurricane activity between Danny and Fred. As a result, the Atlantic’s accumulated cyclone energy, or ACE--a measure of the longevity and strength of each year’s tropical cyclones--has reached a mere 20% of the typical end-of-season total. By comparison, the Northeast Pacific has already produced 32% more ACE than a typical season. El Niño typically favors the Northeast Pacific over the Atlantic in tropical cyclone activity.



Figure 2. Disorganized convection associated with Tropical Depression Fred is shown in this enhanced infrared image from the GOES-East satellite at 1615 GMT (12:15 pm EDT) on Sunday, September 6, 2015. Image credit: NOAA/NESDIS.

Fred refuses to quit
Though it was given a terminal diagnosis days ago, Tropical Depression Fred has shown it isn’t quite ready to leave this mortal coil. Now in its seventh day as a tropical cyclone, Fred’s entire life has unfolded east of longitude 45°W. It became the first hurricane in modern records to pass through the Cape Verde islands, and over the last several days it’s survived in the face of persistent wind shear by generating new convection each time a batch of thunderstorms is sheared away from its center. Downgraded to a tropical depression on Saturday evening, Fred is beginning to interact with an upper-level trough to its northwest and should begin moving more rapidly to the northeast over the next several days, then begin curving back toward the southeast as the trough passes it by. Although the ECMWF model merges Fred with the trough, most other models indicate that Fred will get yet another lease on life over the next several days, as wind shear lessens somewhat. Fred will continue to travel over SSTs that are around 1°C (1.8°F) above average for at least the next five days, so it’s possible Fred could linger as a tropical depression or weak tropical storm throughout this week.

Another healthy wave coming off Africa
African continues to generate an impressive supply of easterly waves that have at least a chance of developing into tropical cyclones as they move into the Atlantic. Our next tropical wave is in the process of moving from West Africa into the Atlantic at a fairly low latitude (see Figure 1 above). SSTs remain unusually high in this region, and I expect we will see this wave emerge into a tropical depression and perhaps become Tropical Storm Henri late this week. Once again, the tendency for high wind shear from the Caribbean northeastward will greatly reduce the odds that any tropical cyclone from the deep Atlantic tropics might approach North America relatively intact.


Figure 3. Sea-surface temperatures (left) and departures from average for this time of year (right), both in degrees C, across the North Atlantic for the week ending on August 29, 2015.

Tropical Storm Linda forms in the Northeast Pacific
Tropical Storm Linda became the latest named system in the Northeast Pacific at 11:00 am EDT Sunday. With winds of 45 mph, Linda is located about 610 miles south of the southern tip of Baja California. Satellite imagery now shows Linda organizing very quickly, and it has a window of a couple of days where it could attain at least Category 1 hurricane strength before it reaches cooler waters and more stable air. Late this week, Linda or its remnants should curve westward before making a run at Baja California. Fortunately, there is no sign at present that Linda will resemble Category 5 Hurricane Linda of 1997. That Linda was the strongest hurricane on record in the eastern Pacific, with top sustained winds of 185 mph. With damage from Linda relatively minor, its name was not retired, but the storm gave a brief scare to southern California. An NHC report notes that some model runs showed a weakening Linda heading toward Baja California or southern California, and special weather statements were issued by the Oxnard, CA, NWS office. (Because lists of hurricane names for the Northeast Pacific and Atlantic are rotated every six years, the same alphabet is being used in 2015 as in 1997--which happens to be the last year that a strong El Niño was in place during the Atlantic/Pacific hurricane season.)


Figure 4. Tropical Storm Linda congeals in the Northeast Pacific, as shown by this infrared image from the GOES-West satellite at 1630 GMT (12:30 pm EDT) on Sunday, September 6, 2015. Image credit: NOAA/NESDIS.

Elsewhere in the Pacific
Downgraded on Saturday night after more than a week as a hurricane, Tropical Storm Jimena is now feeling the effects of marginal SSTs and southwesterly wind shear as it carries out a gradual cyclonic loop north of Hawaii. Jimena’s top sustained winds are down to 60 mph, and they should continue to decrease today and Monday. The GFDL and HWRF models indicate that Jimena could make a comeback late in the week before recurvature into the midlatitudes, but SSTs would be barely supportive of strengthening. The official NHC forecast puts little stock in any late-week revival scenario for Jimena, weakening it to a post-tropical low by Thursday.

Further west, we still have Typhoon Kilo in the open Northwest Pacific. If we include its stint in the Northeast Pacific, Kilo is now in its ninth day of packing hurricane-force winds and its 18th day classified as a tropical cyclone. The latest outlook from the Joint Typhoon Warning Center gives Kilo a final surge of strength to Category 3 status later this week as it begins recurving well east of Japan. Kilo may have 6-7 days left to go as a tropical cyclone, which would leave it well short of the longevity record of 31 days set by Hurricane/Typhoon John (1994).

Bob Henson

Hurricane

TD 7 Forms in the Eastern Atlantic; Likely to Become Tropical Storm Grace

By: Jeff Masters , 3:46 PM GMT on September 05, 2015

Tropical Depression Seven spun into life on Saturday morning in the waters a few hundred miles south of the Cape Verde islands in the Eastern Atlantic, and appears poised to become Tropical Storm Grace by Sunday. TD 7 is under conditions which favor development: light wind shear of 5 - 10 knots, warm ocean waters of 28.3°C (83°F), and a moist atmosphere. The farther south TD 7 stays during the coming week, the greater its chances of development, since a strong band of upper-level winds blowing from west to east will lie a few hundred miles to its north, at a latitude roughly even with Puerto Rico. The atmosphere is also drier to the north. The wave is headed nearly due west today, but will gradually assume more of a west-northwest track. The 8 am EDT Saturday run of the SHIPS model predicted that by Wednesday, TD 7 should gain enough latitude to begin experiencing high wind shear of 20 - 25 knots and a much drier atmosphere. These conditions should act to weaken and possibly destroy TD 7 by the time it makes its closest pass by the northern Lesser Antilles Islands on Friday night or Saturday. Penetration into the Caribbean will be difficult for the storm, as the high wind shear which has dominated the region all summer shows no signs of slackening during the coming ten days.


Figure 1. MODIS image of Tropical Depression Seven in the waters of the Eastern Atlantic a few hundred miles south of the Cape Verde islands, taken at approximately 8:15 am EDT Saturday, September 5, 2015. Image credit: NASA.

Fred hanging on
Persistent Tropical Storm Fred continues to mill about in the waters of the Eastern Atlantic as a minimal-strength tropical storm with 40 mph winds. High wind shear will affect Fred through Monday, keeping the storm weak or possily killing it. However, Fred will encounter lower wind shear and anomalously warm waters of 27.5°C (82°F) by Tuesday, and come close to the Azores as a tropical storm on Thursday or Friday.


Figure 2. Hurricane Ignacio is about to get absorbed by an extratropical storm to its north, as seen by Aqua/MODIS on September 4, 2015. Image credit: NASA.

Pacific quieting down
Two tropical cyclones died today over the North Pacific, leaving two others spinning. We lost Hurricane Ignacio Saturday morning, as it got absorbed by a powerful extratropical storm midway between Hawaii and Alaska's Aleutian Islands. The remains of Ignacio may bring heavy rains to British Columbia on Wednesday. Tropical Storm Kevin, off the coast of Mexico's Baja Peninsula, also met its maker Saturday morning, when high wind shear of 35 knots tore away all of Kevin's heavy thunderstorms. Who's left? Well, in the Central Pacific, we still have weakening Category 1 Hurricane Jimena, with top sustained winds of 80 mph at 11 am EDT Saturday. Jimena will likely pass within 500 miles of Kauai in the Hawaiian Islands on Wednesday. However, high wind shear should weaken Jimena to a tropical depression by then, leaving heavy rains the main threat from the storm. Long-lived Category 1 Typhoon Kilo is now in its 16th day as a tropical cyclone, including a long spell as a major hurricane. Kilo is predicted to steadily re-intensify over the weekend, reaching Category 4 strength by Monday as it moves on a westward path that will likely take it several hundred miles north of Wake Island. Kilo is likely to be around until at least September 11, as it passes to the east of Japan.

An area of disturbed weather in the Northeast Pacific located about 550 miles south-southwest of Manzanillo, Mexico (Invest 98E) is close to tropical depression status as it moves to the northwest at 5 - 10 mph, well offshore from Baja Mexico. This storm is expected to stay out to sea over the next five days. In their 8 am EDT Friday Tropical Weather Outlook, NHC gave 2-day and 5-day odds of development of 90%.

Have a great Labor Day weekend!

Jeff Masters

Hurricane

Watching African Wave 91L; Rare September European Heat Wave Smashes Records

By: Jeff Masters , 3:45 PM GMT on September 04, 2015

A strong tropical wave with plenty of spin and heavy thunderstorm activity (Invest 91L) moved off the coast of Africa on Thursday, and is headed west at 15 - 20 mph, on a path that will take it a few hundred miles south of the Cape Verde islands over the weekend. The 00Z Friday (8 pm EDT Thursday) runs of one of our top three models for predicting tropical cyclone genesis, the GFS model, showed development of 91L into a tropical depression by Tuesday midway between Africa and the Lesser Antilles Islands. In their 8 am EDT Friday Tropical Weather Outlook, NHC gave the wave 2-day and 5-day odds of development of 40% and 60%, respectively. The tropical Atlantic is relatively moist, has the highest sea surface temperatures of the year, and is expected to have low to moderate wind shear, conditions which favor development. The wave should take about 6 - 8 days to make it to the Lesser Antilles Islands.


Figure 1. MODIS image of Invest 91L off the coast of Africa taken at approximately 8:15 am EDT Friday, September 4, 2015. Image credit: NASA.

Fred barely alive
Tropical Depression Fred continues to barely hang on as a tropical cyclone in the waters of the Eastern Atlantic, but high wind shear is expected to kill Fred by Saturday. However, Fred could spring back to life in 3 - 5 days, when the storm will encounter lower wind shear and anomalously warm waters of 27.5°C (82°F), over 500 miles southwest of the Azores Islands. Fred could affect the Azores 6 - 7 days from now, but it is too early to judge the risks of this.

The remains of Tropical Storm Erika are still generating some disorganized shower activity off the Southeast U.S. coast, but high wind shear will prevent re-development.


Figure 2. From left to right: Typhoon Kilo, Hurricane Ignacio, and Hurricane Jimena spin across the Pacific Ocean as seen by Aqua/MODIS at 02:40 UTC September 3, 2015. Image credit: NASA.

A Busy Pacific for Tropical Cyclones
Four tropical cyclones continue to spin over the North Pacific, though none are expected to threaten land over the next five days. Tropical Storm Kevin in the Eastern Pacific, with top sustained winds of 60 mph at 11 am EDT Friday, is feeding moisture in the Southwest U.S. monsoon, and will contribute to isolated heavy rains over Arizona and New Mexico over the next few days. No flood watches or warnings were up on Friday for the anticipated rain, though. Kevin is expected to turn west and head out to sea, eventually succumbing to high wind shear and mid-level dry air. In the Central Pacific, Hurricane Jimena is slowly weakening, with top sustained winds of 85 mph at 11 EDT Friday. Recent runs of the GFS and European models continue to predict that Jimena will approach Hawaii from the northeast late next week as a tropical storm, and pass within 200 miles of the islands. Meanwhile, Hurricane Ignacio, now a Category 1 storm north of Hawaii, is weakening as it heads north towards the Gulf of Alaska. Ignacio is expected to transition to a powerful extratropical storm by Monday, and bring heavy rains to Britich Columbia on Tuesday. Long-lived Typhoon Kilo is now in its 15th day as a tropical cyclone, including a long spell as a major hurricane. Kilo is predicted to steadily re-intensify over the weekend, reaching Category 4 strength by Sunday as it moves on a westward path that will likely take it several hundred miles north of Wake Island. Kilo is likely to be around until at least September 11, and may pose a threat to Japan 6 - 7 days from now.

One "sleeper" system to watch is an area of disturbed weather in the Northeast Pacific located several hundred miles south-southwest of Manzanillo, Mexico. Slow development of this system is possible during the next several days as the low moves northwestward and gradually merges with another disturbance to its west. The models are not handling this merger well, and this system may end up being of concern to Mexico's Baja Peninsula. In their 8 am EDT Friday Tropical Weather Outlook, NHC gave 2-day and 5-day odds of development of 10% and 40%, respectively.

Rare September Heat Wave Scorches Europe
Meteorological summer is over in Europe, but a rare and extraordinarily intense heat wave has kept its grip on much of the continent during early September. Hundreds of European cities broke all-time September heat records the past three days; some stations with long periods of record exceeding a century saw their records smashed by 7 - 8°F--"a margin rarely seen before in the world," in the words of weather records researcher Maximiliano Herrera, who has been tabulating the new records.


Figure 3. Historians recover relics from the 17th century on the bed of the Vistula River in Warsaw, Poland on September 3, 2015. The water level of the Vistula, Poland's largest river, is at its lowest level since measurements began in 1789, due to severe drought conditions. The treasures being excavated were looted by an invading Swedish army in the mid-17th century and got buried in the Vistula when a Swedish barge sank. Jewish tombstones and wreckage from a WWII fighter plane have also been uncovered this summer from the Vistula and its tributaries due to the low water levels. Image credit: JANEK SKARZYNSKI/AFP/Getty Images.

September 1, 2015: a rare day in the annuals of climatology
The carnage began on September 1, with September national heat records falling in eight countries. Notably, the new national heat record set in Lithuania was more than 3°C (5.4°F) higher than the previous September record--an astonishing margin for a monthly national record in a nation with dozens of reliable stations with a period of record extending back nearly 150 years. Here are the eight nations that set new September all-time heat records on September 1, 2015, according to Maximiliano Herrera:

Moldova: Tiraspol, 38.4°C (101.1°F)
Ukraine: Voznesens'k, 38.8°C (101.8°F)
Austria: Pottschach, 36.0°C (96.8°F)
Czech Republic: Javornik, 37.4°C (99.3°F)
Slovakia: Michalovce, 36.4°C (97.5°F)
Poland:  Tarnow, 36.8°C (98.2°F)
Belarus: Zitkovici, 35.6°C (96.1°F)
Lithuania: Druskininkai, 35.1°C (95.2°F)

All-time September heat records were smashed at individual stations in many other countries, including Russia, Romania, Bulgaria, Serbia, Montenegro, Macedonia, Kosovo, Bosnia and Herzegovina, Croatia, Slovenia, Italy, San Marino, Hungary, and Germany, with 48 stations in Germany alone setting new all-time September heat records (thanks go to Dr. Michael Theusner for this stat.) Some stations with more than a century of data even managed to beat their ABSOLUTE records for any month.


Figure 4. Severe drought had much of Europe in its grip by mid-August, 2015. Image credit: European Drought Observatory.

September 2 and beyond: more record heat
The incredible heat continued on September 2, shifting eastwards some, with a 38.6°C (101.5°F) at Falesti, Moldava beating that nation's all-time September heat record set just the previous day. Ukraine tied its national record, just set the previous day. The extreme heat backed off considerably on September 3 and 4, but will build back in again over Southeast Europe over the weekend, with more all-time September heat records likely to fall.

European drought cost this summer: $2.7 billion
It's been a incredible summer for extreme heat in Europe, with Germany setting its all-time heat record (twice), and with hundreds of stations having long periods of record setting all-time heat records. The heat has been responsible for hundreds of heat deaths in Europe, and according to the August 2015 Catastrophe Report from insurance broker Aon Benfield, drought in Romania, Poland, and the Czech Republic this summer has cost at least $2.7 billion--just below the $3 billion price tag of the California drought.

We’ll be back with an update on the tropics on Saturday. Have a great Labor Day weekend!

I'll be on the Weather Underground TV show (#WUTV on Twitter) tonight on The Weather Channel. The show airs between 6:00 and 8:00 pm EDT. If you don’t have access to TWC on cable, you can still access selected clips from each episode, live streaming of online-only content, and a WUTV chatroom, all on the Weather Underground WUTV website.

Jeff Masters

Hurricane heat Drought

Arctic Sea Ice May Reach Second-Lowest Extent on Record This Month

By: Bob Henson and Jeff Masters , 4:18 PM GMT on September 03, 2015

A burst of late-season loss over the last several weeks has put the Arctic Ocean’s ice cover within reach of the lowest extent observed in any year except 2012. The extent values tracked by the National Snow and Ice Data Center, or NSIDC (see Figure 1), show that 2015 has caught up to several other recent years in the amount of ice depleted, and is poised to surpass 2011 and 2007 if the rapid loss continues. The milestone is a timely one, given this week’s historic Alaskan visit by President Barack Obama.

NSIDC reviewed the near-term outlook for sea ice in an update posted on Wednesday: “There is still a possibility that 2015 extent will be lower than 4.3 million square kilometers, the third lowest sea ice extent, surpassing the 2011 sea ice extent minimum, and a small chance of surpassing 2007, resulting in the second-lowest daily minimum. This assumes that we continue to have sea ice loss rates at least as fast as those of 2010. This was indeed the case for the final ten days of August 2015.”

As explained by NSIDC with a swiss-cheese analogy, sea ice extent refers to the amount of ocean covered by at least 15 percent ice concentration (the dimensions of the slice of cheese), whereas sea ice area is the literal amount of ocean covered by ice, not counting the holes. Arctic ice normally reaches its maximum extent in March and its minimum in September. The ice extent drops in spring and summer largely as a result of melting (from below and above), though it can also be influenced by compaction (which pushes broken-up areas of ice together, reducing the total ice extent). Another factor is a pattern of atmospheric pressure called the Arctic Dipole, which favors Asia-to-Europe cross-polar flow that can push ice out the Fram Strait into the North Atlantic, hastening ice depletion.



Figure 1. Sea ice extent across the Arctic Ocean for the period August-November, 1979-2015. This year’s extent was just over 4.6 million square kilometers on September 2, and dropping rapidly, with only the 2012 curve falling much lower. Nine of the 10 lowest extent values have occurred within the last decade. Image credit: NSIDC.


There’s still plenty of darkness and cold air to foster ice-cover regrowth across most of the Arctic each winter, but the summer minima have plummeted in recent decades (see Figure 1). With just weeks left before net ice expansion resumes, it’s all but impossible for 2015 to catch up to 2012. That year saw the lowest extent since satellite records began in 1979 (3.41 million square km, or about 50% below the typical minimum observed in the 1980s and 1990s). However, a minimum in the vicinity of 4.2 to 4.3 million sq km seems within reach. That would be well below the average value of 4.8 million sq km predicted by an array of 38 participants in the latest monthly Sea Ice Outlook produced by the Sea Ice Prediction Network. By that time this forecast was issued (August 20), Arctic ice extent had come off near record-low values for late spring, recovered somewhat by early summer—thanks in part to a cold June across the Arctic, with relatively little melting--and dipped again in August, with fairly steady losses through the month. Then came a surprisingly strong cyclone that developed across the Beaufort Sea last week. High winds and seas from that storm helped weaken a large arm of multi-year ice extending from the central Arctic into the Beaufort Sea. The storm also brought punishing waves and erosion to the Alaskan coast near Barrow (see Figure 2).


Figure 2. High surf batters the coast near downtown Barrow, Alaska, on August 27, 2015. Image source: Barrow Sea Ice Webcam, tweeted by Brian Brettschneider


Figure 3. This intense surface cyclone disrupted a large chunk of Arctic sea ice that extended from the Central Arctic into the Beaufort Sea. Analysis for 0000 GMT on August 27, 2015, shows sea level pressure (in green); potential temperature at the tropopause, a marker of upper-level energy that can help foster surface cyclones (in black); and the extent of Arctic sea ice (grey shading, with concentration fraction shown by the bar at right). A corresponding animation shows the sequence of events beginning on August 16 and segues into a model prediction from August 2 to September 9. Image credit: Steven Cavallo, University of Oklahoma.


What’s ahead this month and beyond?
“It is still pretty stormy over the Arctic,” said Steven Cavallo, a University of Oklahoma meteorologist who specializes in polar weather. Cavallo has researched tropopause polar vortices (TPVs) and their relationship to surface cyclones. “There are a lot of TPVs around, meaning the potential for surface cyclone formation is high, so I think the forecast sensitivity is very high right now and there could still be some significant ice loss.” Recent model runs have flip-flopped in predicting additional strong cyclones over the Arctic over the next few days. Cavallo hypothesizes this could be related to the difficult-to-predict effects of tropical cyclones recurving into the polar jet stream. At the Arctic Sea Ice Blog and Forum, there’s been a lot of conversation along these lines. “People on the forum are speculating on and off about a 'train' of cyclones, either Atlantic or Pacific, injecting heat and moisture into the Arctic,” said blog/forum founder Neven Acropolis in an email. Two good places to follow the dialogue are “The 2015 melting season” thread and Acropolis’s own excellent posts.


Figure 4. Sea ice concentration for September 1, 2015, as calculated by the National Snow and Ice Data Center. Areas shaded in lighter blue denote reduced concentration (area) within the overall bounds of ice extent. Image credit: NSIDC.


The ice that’s managing to persist across the Arctic this summer doesn’t look especially healthy. Polar climate specialist Jennifer Francis (Rutgers University) calls out the warning signs conveyed in the most recent ice concentration image from NSIDC (see Figure 4, at right). “Much of the ice that's left is either slushy, severely broken up, or covered in melt ponds,” Francis noted. Depletion is especially large on the Pacific side of the Arctic, she added, which recent work suggests may favor a severe winter in parts of eastern North America. Much research in the last few years by Francis and others has worked to draw connections between Arctic sea ice loss, high-latitude warming, and midlatitude winter weather. A new entry in this mini-discipline is a paper published last week in Nature Geoscience that links two modes of warm Arctic weather to subsequent winter cold downstream across East Asia and North America.

The power of this year’s still-strengthening El Niño event may be enough to swamp whatever influence the decline of Arctic sea ice might have on the upcoming winter across North America. Sea-surface temperatures (SSTs) are cooling over the western tropical Pacific in tandem with the building El Niño warmth over the eastern tropical Pacific. A number of studies (nicely summarized by Daniel Swain at California Weather Blog) suggest that the western-Pacific cooling will help lead to more storminess over the Gulf of Alaska, which in turn could finally erode the persistently warm SSTs and the “ridiculously resilient ridge” of high pressure that have prevailed in that area for most of the last two years. If so, a pathway will be carved for the classic El Niño signature of very mild winter temperatures across most of Canada and the northern United States, in line with the latest seasonal forecasts from NOAA. If, instead, we see a third consecutive winter of unusual cold across the U.S. Midwest and Northeast, it’ll be a strong sign that another player is onstage. Judah Cohen (Atmospheric and Environmental Research) bases his North American winter forecasts in part on the apparent relationship between low Arctic sea ice extent and cold Northern Hemisphere winters. “I really do think that this could be a very interesting winter and could be very informative on the interplay of tropical vs. Arctic forcing,” said Cohen in an email. “Can the Arctic, as a forcing agent of mid-latitude weather, finally step out out of the shadow of the tropics or not?”



Figure 5. Both the Arctic and Antarctic rack up more than 12 million square klilometers of sea ice extent each winter, but the summer ice depletion is greater in the Antarctic, where the ice sits at lower latitudes. Image credit: The Cryosphere Today/University of Illinois at Urbana-Champaign.

Why it matters
Although a coating of ice does return to most of the Arctic Ocean each winter, the persistence of ice through the summer is a vital part of the region’s ecosystem. Polar bears, ringed seals, and other wildlife use the ice as a platform for hunting prey and raising their young. Many indigenous residents of the lands circling the Arctic have also relied on the presence of year-round ice for centuries. The picture is far different at the other end of the world: instead of being surrounded by ocean, the South Pole lies at the heart of the landmass of Antarctica. Sea ice in this hemisphere develops on the fringes of Antarctica, which puts it at a lower latitude than most Arctic sea ice. As a result, nearly all of the ice that forms each winter around Antarctica melts back each summer. The average wintertime extent of ice around Antarctica has actually grown slightly in recent years, for reasons not fully understood. This is often falsely presented as “balancing” the loss of Arctic sea ice, but the Arctic loss is far more substantial than the Antarctic gain, and much more important to regional climate, ecology, and economy. Ice-free navigation is now once again possible in the Arctic along the coast of Canada (the southern route of the fabled Northwest Passage), and has been open for over a month along the coast of Russia (the Northeast Passage or Northern Sea Route.) Mariners have been attempting to sail these passages since 1497; the first time they were open for ice-free navigation without an icebreaker was in 2005 for the Northeast Passage and 2007 for the Northwest Passage. The continuing erosion of summer ice cover in the Arctic has stoked interest in expanding industrial activity across the region, including oil and gas development--an ironic turn of events, given the role of fossil-fuel-produced greenhouse gases in the worldwide warming of recent decades.

Tropical Atlantic: Tenacious Fred hangs on
Tropical Storm Fred has been in “never say die” mode, hanging on as a minimal tropical storm on Thursday morning as it drifted across the eastern Atlantic. New thunderstorms blossomed on the east side of Fred’s circulation center on Wednesday night into Thursday, despite stout wind shear of more than 35 mph. By midday Thursday, only a much smaller patch of convection was located just north of Fred’s exposed center. The shear is expected to increase, and the National Hurricane Center expects Fred to become a remnant low by Friday. NHC is mentioning the possibility, though, that Fred could spring back to life in five days, when the storm will encounter lower wind shear and anomalously warm waters of 27.5°C (82°F) over 500 miles southwest of the Azores Islands.

New tropical wave moving off the coast of Africa has potential to develop
A strong tropical wave with plenty of spin and heavy thunderstorm activity will move off the coast of Africa by Thursday night, and has the potential to become a tropical depression early next week as the storm moves west at 15 - 20 mph. The 00Z Thursday (8 pm EDT Wednesday) runs of two of our top three models for predicting tropical cyclone genesis, the GFS and European models, predicted that this new wave would become a tropical depression in the waters southwest of the Cape Verde islands by Monday. In their 8 am EDT Thursday Tropical Weather Outlook, NHC gave the wave 2-day and 5-day odds of development of 10% and 40%, respectively. The tropical Atlantic is relatively moist, has the highest sea surface temperatures of the year, and is expected to have low to moderate wind shear, conditions which favor development. The wave should take about 7 - 8 days to make it to the Lesser Antilles Islands.


Figure 6.Typhoon Kilo and Hurricanes Ignacio and Jimena, all captured in this infrared image from the GOES-West satellite at 1330 GMT (9:30 am) Thursday, September 3, 2015. Image credit: NOAA/NHC and Michael Lowry, The Weather Channel.

Pacific continues to bristle with tropical cyclones
The Northeast Pacific has a new named system, Tropical Storm Kevin. As of 11 am EDT Thursday, Kevin’s top sustained winds had increased to 50 mph. Kevin is expected to live out the rest of its life below hurricane strength over open water before increasing amounts of shear and mid-level dry air take their toll. Some moisture associated with Kevin will be working its way into Colorado and New Mexico through Saturday ahead of a large upper-level trough approaching the region, enhancing shower and thunderstorm activity there. In the Central Pacific, powerful Hurricane Jimena is very slowly weakening but remains a high-end Category 2 as it embarks on a broad cyclonic loop well northeast of Hawaii over the next few days. We’ll have to keep an eye on Jimena in the long range, as the recent runs of the GFS and European models bring Jimena back toward Hawaii from the northeast late next week, still as a tropical storm. Such a scenario might be dismissed out of hand in any other year, but with SSTs so warm in the Central and Northeast Pacific, Jimena could conceivably remain over waters at or above the threshold of 26°C (79°F) over most or all of such a trek. Meanwhile, Hurricane Ignacio, now a Category 1 storm north of Hawaii, is also weakening but remains impressively well-structured, with extensive spiral banding. Ignacio is on track to plow into the Gulf of Alaska as a powerful extratropical storm by early next week. En route, Ignacio will pass over unusually warm waters along the way, with sea-surface temperatures up to 3-4°C (5.4-7.2°F) above average (though eventually too cool to support Ignacio as a tropical cyclone).

Ultra-resilient Typhoon Kilo is now in its 14th day as a tropical cyclone, including a long spell as a major hurricane. Kilo is predicted to steadily reintensify over the next 3-4 days, again reaching Category 4 strength by Tuesday as it moves on a westward loop that will likely take it several hundred miles north of Wake Island. In the long range, Kilo may pose a threat to Japan.

We’ll be back with our next update on Friday.

Bob Henson and Jeff Masters


Arctic Climate Change Hurricane Sea Ice

U.S. Wildfires 2015: Are The Worst Yet To Come?

By: Bob Henson and Jeff Masters , 4:38 PM GMT on September 02, 2015

Thus far, 2015 has been one of the worst U.S. wildland fire seasons since modern records began. More than 8.2 million acres have burned across the nation as of September 1, an area larger than Massachusetts and Rhode Island combined. Across the last ten years, that’s the largest amount of fire-scorched U.S. acreage for the January-August period, and it’s close to 50% above the decadal year-to-date average. We are well ahead of the pace set in 2007, when 9,328,045 acres burned, the highest annual total in records going back to 1960.



Figure 1. Flames from a backfire operation burn behind an emergency vehicle near the Rocky Fire on August 3, 2015, near Clearlake, California, north of San Francisco. Some 3,000 firefighters battled the Rocky Fire, which burned more than 80,000 acres and destroyed almost 100 residences and outbuildings. Image credit: Justin Sullivan/Getty images.


There’s a more complex story hiding behind these factoids. Certainly there have been some intense and large fires across the Pacific Northwest, pumping out smoke that’s reddened skies and clotted lungs across large swaths of the nation. But up until August, the main factor behind this year’s large wildfire acreage (as explained by Tom Yulsman at Discover’s ImaGeo blog) was the extent of fire in Alaska. More than 5.1 million acres had burned across the state as of September 1, most of it by midsummer. With Alaska’s fire activity now slowing down, the state’s total affected acreage will likely rank second behind 2004, when a total of 6,590,140 Alaskan acres went up in flames.

It was clear by early summer that the Pacific Northwest was in line for a potentially rough fire season, with long streches of record spring and summer heat following a winter with record-low snowpack. Simply having a parched landscape doesn’t automatically translate into big fire, though. If strong, dry winds are absent; if fires aren’t triggered by lightning and/or human activity; and/or if firefighters manage to tamp down fires quickly, then the potential for disaster may go unrealized. Wildfires didn’t begin taking full advantage of the Pacific Northwest’s primed-for-fire condition until mid-August, when the Okanogan Complex roared to life across north-central Washington. Now the state’s largest assemblage of wildfires on record, the Okanogan Complex (40 percent contained as of Tuedsay) has destroyed more than 170 homes.


Figure 2.The Significant Wildland Fire Potential Outlook for September 2015 shows above-normal risk across parts of four western states, as well as a small part of central Texas. Image credit: National Interagency Coordination Center.


On August 13, officials upgraded the National Preparedness Level for wildland fire to category 5, the highest, meaning that multiple major fires have the potential to exhaust all of the nation’s firefighting resources. This is the first category-5 ranking since a week-long stretch in August 2013, and the fifth such period in the last ten years. Cooler temperatures should continue to tamp down the fire risk in Alaska this month, but it’s far too soon for other western states to rest easy. The latest monthly outlooks for wildland fire potential, issued on Monday by the National Interagency Coordination Center, show an above-normal risk of significant wildfire in September across eastern Washington, northeast Oregon, and far northwest Montana, as well as the Sierra Nevada and coastal mountains south of the Bay Area in California. By October, the risk is expected to return to near normal over the Pacific Northwest and central California, but the highly populated belt of Southern California is still targeted for above-normal risk.

Why fall is the most-feared time for wildfire in California
California’s Mediterranean climate means that rainfall is focused in the period from late fall into spring, with the landscape then getting progressively drier until the next wet season kicks in. This sets up prime conditions for wildland fire during the typically warm, dry weather of September and October, sometimes goosed by strong offshore winds (dubbed the Santa Ana wind in the L.A. area). Late October 1991 brought the horrific Oakland hills firestorm, which destroyed more than 2,800 homes and killed 25 people, and Southern California’s record-setting wildfire seasons of 2003 and 2007 both peaked in October.


Figure 3. Meg Tallberg (left), whose home was not damaged by fire, offers her support to neighbor and friend Jenny Fratis (right), whose house (background) was destroyed in the Witch Fire, as residents returned to Rancho Bernardo in California's San Diego County on 25 October, 2007. Image credit: Robyn Beck/AFP/Getty Images.


This year, California is entering fire season after four years of drought, culminating in what’s been the warmest year for California in more than a century of recordkeeping. Although some unusual summer rains have provided dabs of relief across the far southeastern desert, much of the landscape across central and southern California remains tinder-dry. Some 46% of the state is now in exceptional drought, the highest ranking assigned by the National Drought Mitigation Center in its weekly U.S. Drought Monitor. That’s down a bit from 58% at this time a year ago, but the impacts of long-term drought in the hardest-hit areas remain severe. In August, a study from the University of California, Davis, estimated that the ongoing drought will cost California about $2.7 billion in 2015. Several intense, destructive fires have already struck the state, including the small but frightening, interstate-jumping North Fire east of Los Angeles in mid-July and the huge Rocky and Jerusalem Fires north of San Francisco in late July/early August.

The main questions awaiting the West’s fire-prone areas this autumn--questions that forecasters can’t answer with confidence--is how often and where windy frontal systems and/or strong offshore flow will materialize. NOAA’s seasonal outlook for September through November maintains above-average temperatures throughout the West Coast states, with precipitation below average in the Pacific Northwest and above average over southern California. The strengthening El Niño gives SoCal a good chance at above-average rains this winter, but the heaviest Niño-related rains often don't arrive till December/January.


Figure 4. While in Alaska, WU art director Lauren Moyer captured the not-so-common sight of a virtually cloud-free Mount Denali on August 3, 2015. In the foreground is a WU personal weather station, MEVCA2. Image credit: wunderphotographer moyerdestroyer.

Climate change and wildfire risk
One of the key points made by President Barack Obama in his visit to Alaska this week (including Wednesday’s scheduled stop north of the Arctic Circle, the first ever by a president in office) is the role of human-induced climate change in exacerbating wildfire risk across the state. In a speech delivered Monday in Anchorage, Obama noted: “Alaska’s fire season is now more than a month longer than it was in 1950. At one point this summer, more than 300 wildfires were burning at once.” The lengthening fire season in Alaska reflects a global trend: a new open-access analysis published in Nature Comunications in July found that 25% of Earth’s vegetated surface saw fire seasons grow longer from 1979 to 2013 by an average of close to 20%.



Figure 5. Areas that have experienced changes in the frequency of long fire weather seasons (at least one standard deviation above the historical average) during the period 1996-2013 compared with 1979–1996. Reds indicate areas where fire weather seasons have lengthened or long fire weather seasons have become more frequent. Blues indicate areas where fire weather seasons have shortened or long fire weather seasons have become less frequent. Image credit: Figure 3(b), “Climate-induced variations in global wildfire danger from 1979 to 2013,” W. Matt Jolly et al., Nature Communications 2013.


Alaska has warmed more quickly than the rest of the nation over the last 60 years, with annual average temperatures in Alaska climbing by about 3.0°F over the period from 1949 to 2014. The warming has come in phases, according to the Alaska Climate Research Center, with temperatures spiking in the 1970s and then plateauing at a “new normal” for several decades before a new level of warmth was hit in 2014, continuing into this year. The period Jan-July 2015 was Alaska’s second warmest in 91 years of recordkeeping, according to NOAA’s National Centers for Environmental Information. The U.S. National Climate Assessment, published in 2014, had this to say about Alaska’s evolving climate and fire risk: “Both wetland drying and the increased frequency of warm dry summers and associated thunderstorms have led to more large fires in the last ten years than in any decade since record-keeping began in the 1940s….More extensive and severe wildfires could shift the forests of Interior Alaska during this century from dominance by spruce to broadleaf trees for the first time in the past 4,000 to 6,000 years.”



Figure 6. Annual average temperature across Alaska, 1949 – 2014. Image credit: Alaska Climate Research Center.


Wildfires are the complex product of many variables, including forest management, fire suppression, temperatures and moisture, ignition sources, and firefighting practices. Prior to European settlement, gigantic fires were part of the natural ecosystems across much of North America. In a dot.earth blog post from 2013, Andrew Revkin discusses the historical context of U.S. fire suppression and its role in helping lay the groundwork for today’s megafires. Whatever factors have led to the forests we have today, their ability to burn intensely is being stoked by rising temperatures that intensify the impacts of naturally occurring drought, a point illustrated vividly this year from California to Washington and emphasized in several recent studies (including this one, published just this week in Geophysical Research Letters). There will be some inevitable randomness in the final, fateful steps (weather events, arsonists, etc.) that lead from a particular parched landscape to a devastating fire. We’re very unlikely to see the entire West in flames anytime soon (thankfully!), but it’s reasonable to expect that heat unprecedented in modern times and dried-out vegetation will sometimes lead to fires more intense and/or widespread than ever before seen by residents of a given area. With ever-larger numbers of Americans choosing to live amid western forests, and cities such as Oakland and Los Angeles adjoining fire-prone areas, the risks to life and property will only rise with time.



Figure 7. It’s a hurricane! It’s a typhoon! It’s both! Dan Lindsey (CIRA) posted this tongue-in-cheek analysis of Kilo, using a visible image from Japan’s Himiwari-8 satellite, as the storm straddled the International Date Line on September 1, 2015. Hurricanes are reclassified as typhoons when they move west across the Date Line. The Sydney Morning News asked whether Kilo should be called a “hurriphoon” or a “typhane.” Kilo was officially reclassified from Hurricane Kilo to Typhoon Kilo at 0600 GMT on September 1. Image credit: RAMMB/CIRA/JMA.


Tropics calming down
After weeks of hyperactivity, the Northern Hemisphere tropics are beginning to calm down for the time being. The 00Z Thursday morning run of the GFS model was not predicting any new tropical cyclones to develop anywhere in the world during the next seven days, though the European model was showing possible development next week of a tropical wave expected to come off the coast of Africa this Friday. This wave is expected to move westwards at about 15 mph towards the Lesser Antilles Islands; NHC did not mention this wave in their 8 am EDT Wednesday Tropical Weather Outlook. Tropical Storm Fred continues to weaken in the far eastern North Atlantic; likewise, Hurricane Jimena in the Northeast Pacific and Hurricane Ignacio in the Central Pacific are gradually spinning down. Only Typhoon Kilo is expected to resurge over the next several days. Currently almost stationary just west of the International Date Line, Kilo should gradually accelerate westward across warm waters south of a subtropical ridge, gaining strength along the way and perhaps reaching Category 4 status once again by the end of the week. Today (September 2) is Kilo’s 13th day as a tropical cyclone, and this morning's run of the GFS model predicted that Kilo would remain a tropical cyclone for at least nine more days. According to the National Hurricane Center, the longest-lived tropical cyclone in the satellite era is Hurricane/Typhoon John, which was tracked for 31 days during August and September 1994.

WU contributor Phil Klotzbach has a new post on the recent frenzy of North Central Pacific activity; see also his two-part entry on record-setting action across the Northern Hemisphere as a whole, posted on August 25 and August 28.

We’ll be back with another post on Thursday.

Bob Henson and Jeff Masters


Fire Climate Change Hurricane

Fred Weakens after Lashing Cape Verde Islands

By: Bob Henson , 4:21 PM GMT on September 01, 2015

Tropical Storm Fred, downgraded from hurricane status on Monday night, carved its way into the record books as it made the most direct hurricane strike on the Cape Verde islands in modern records. Fred has since weakened while plowing into a large batch of dry, dusty Saharan air. As of 11:00 am EDT Tuesday, Fred was located about 250 miles northwest of the islands, with top sustained winds down to 50 mph. The National Hurricane Center expects that Fred will continue to steadily weaken over the next couple of days as it moves northwestward.

At its height, Fred boasted prominent spiral banding, and microwave data revealed a well-defined eye, although it was mostly cloud-covered in visible satellite imagery. Although it appears that Fred’s center did not make a landfall on any of the islands, it came within roughly 20 miles of the northeastern island of Boa Vista and the northwestern islands of Sao Nicolau and Santo Antau, so Fred’s eyewall may have affected each of these areas. Boa Vista was on the stronger right-hand side of the storm, whereas Sao Nicolau and Santo Antau fell on the weaker left-hand side of Fred. Either way, many residents unaccustomed to extreme weather could have experienced very strong winds and heavy rain. Several weather stations on the islands did not report at the height of the storm, so our picture of what happened is still incomplete. Arlindo Lima, president of the National Civil Protection Service for the Republic of Cabo Verde (the nation’s official name in all languages since 2013) reported that Boa Visa and Sal, both north of Fred’s track, were the hardest-hit islands, with about 120 islanders displaced to a shelter. The nation’s airports were closed ahead of Fred’s arrival. Reports and photos on a Facebook page dedicated to Boa Vista suggest widespread but mostly minor damage, with trees and communication towers knocked down. There were no reports of casualties as of early Tuesday, according to an AFP update. Storm surge expert Hal Needham (Louisiana State University) was not expecting the surge from Fred to be extreme, since the hurricane had not had much time as a tropical cyclone to push large amounts of water ahead of it. The Cape Verde news site A Naca reported flooding related to Fred in the West African republic of Guinea-Bissau, with flooding and some evacuations in the capital city of Bissau. (Thanks to WU member barbamz for several of the websites above, translated via Google Translate.)


Figure 1. Official positions for Hurricane Fred, as provided by the National Hurricane Center, suggest that the hurricane wove its way around the northern Cape Verde islands without making a complete landfall, although Fred’s eyewall may have affected several islands. Image generated by WU’s Storm app for iPad.


Figure 2. MODIS image of Hurricane Fred from NASA's Terra satellite, taken at approximately 11:15 am EDT on Monda,y August 31, 2015. At the time, Fred had top sustained winds of 85 mph. Image credit: NASA.


Figure 3. “Hot towers” (orange) extending up to 52,000 feet (16.2 km) were evident near the center of intensifying Tropical Storm Fred at 0236 GMT Sunday, August 30 (10:36 pm EDT Saturday), not long after it had moved off the west coast of Africa. As NASA’s Global Precipitation Mission satellite examined the developing Fred, it found rainfall occurring at close to 128 mm (5.0 inches) per hour within the hot towers. Fast-growing Fred was designated as a tropical depression about three hours after this image was collected; it became a tropical storm at 5:00 am EDT Sunday and a hurricane at 2:00 am EDT Monday. Credit: NASA/JAXA/SSAI, Hal Pierce


Fred the record-setter
Fred’s arrival led to a “fountain of ‘firsts’,” as Capital Weather Gang put it. Among them:

--Fred was the easternmost hurricane to develop in the tropical Atlantic in NOAA’s HURDAT database, which extends back to 1851. (These records are less complete and reliable prior to the advent of satellite monitoring in the 1960s.) Fred was dubbed a hurricane at 2:00 am EDT Sunday while at 15.3°N, 22.5°W. During the record-setting 2005 Atlantic season, Hurricane Vince actually formed further east than Fred (18.9°W), but at a much higher latitude (34.1°N).

--Fred made the closest approach to a Cape Verde island of any hurricane in the HURDAT database. The only other hurricane to affect the islands, other than glancing blows from well to the south, was an unnamed 1892 storm that moved between the two clusters of islands that makes up the Republic of Cabo Verde. As Jeff Masters and I noted yesterday, independent hurricane scholar Mike Chenoweth has identified the most damaging storm known to affect the islands: an apparent hurricane on September 2, 1850 (predating the HURDAT database) that reportedly destroyed more than 600 homes and wiped out crops. See our Monday post for more details from Mike’s research.

--The Cape Verde islands were under their first-ever official hurricane warning on Monday.

--Courtesy of Fred, we now have the first satellite images ever collected of a hurricane over the Cape Verde islands.


New tropical wave expected to emerge from Africa on Thursday
A tropical wave currently over west-central Africa is expected to move off the coast of Africa on Thursday, at a location a few hundred miles southeast of the Cape Verde islands. The Tuesday morning runs of the GFS model predicted some slow development of this wave late in the week as it moves west at 15 - 20 mph towards the Lesser Antilles Islands. Our other two reliable models for predicting tropical cyclone genesis, the European and UKMET models, depicted an atmosphere with higher wind shear, and little or no development of the new tropical wave. In their 8 am EDT Tuesday Tropical Weather Outlook, NHC gave the wave 2-day and 5-day odds of development of 0% and 20%, respectively.


Pacific staying busy
Several potent tropical cyclones are racking up the accumulated cyclone energy (ACE) across the Pacific, even as El Niño continues to keep the Atlantic relatively suppressed. Accumulated cyclone energy, or "ACE," is used to express the activity and destructive potential of individual tropical cyclones and entire tropical cyclone seasons. ACE is calculated as the square of the wind speed every 6 hours, and is then scaled by a factor of 10,000 for usability. For the Northern Hemisphere as a whole, the total ACE (now more than 500 units) is far ahead of any other year through August 31, according to WU contributor Phil Klotzbach (Colorado State University). The previous record-holder, 2004, had a total of 389 ACE units by this point. The record for an entire year was 853 ACE units, achieved in 1992.


Figure 4. Accumulated cyclone energy (ACE) through August 31 for each year up since reliable records began in 1971 in the Northeast Pacific. Image credit: Phil Klotzbach, Colorado State University.

Most of this year’s amazing ACE can be attributed to a number of typhoons and hurricanes in the North Pacific that have been both powerful and long-lived. From Saturday into Sunday, Hurricane Kilo, Hurricane Ignacio, and Hurricane Jimena were all at Category 4 strength--the first time since the satellite era began in the 1960s that three simultaneous Category 4 hurricanes had existed in the waters of the Eastern Pacific, east of the International Date Line. Ignacio continues to slowly decline as it heads northwest of Hawaii, while Jimena—now in its fourth day as a major hurricane—should weaken only gradually as it moves northward well east of Hawaii. A new system in the Northeast Pacific, Tropical Depression 14-E, is expected to become a minimal tropical storm at best as its heads toward Baja California.

For sheer longevity, Hurricane Kilo--which will become Typhoon Kilo when it crosses the Date Line over the next few hours--appears to be going for the gold. Today (September 1) is Kilo’s 12th day as a tropical cyclone and third day as a major hurricane. The Joint Typhoon Warning Center keeps Kilo as a major tropical cyclone for the next five days as it drifts across the open North Pacific, restrengthening from Category 3 to Category 4 levels by Day 3. Klotzbach notes that the ECMWF model keeps Kilo going as a strong tropical cyclone for at least 10 more days, possibly challenging the record of about 11 total days that Hurricane Ioke racked up as a major tropical cyclone. According to the National Hurricane Center, the longest-lived tropical cyclone in the satellite era is Hurricane/Typhoon John, which was tracked for 31 days during August and September 1994. In the Atlantic, the record-holder is 1971’s Hurricane Ginger (28 days).

Phil Klotzbach has much more on the record-setting Northern Hemisphere tropical cyclone season in a two-part Weather Underground blog entry posted on August 25 and August 28.

We’ll have our next post on Wednesday.

Bob Henson





Hurricane


The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

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About

Cat 6 lead authors: WU cofounder Dr. Jeff Masters (right), who flew w/NOAA Hurricane Hunters 1986-1990, & WU meteorologist Bob Henson, @bhensonweather