Category 6™

Not a trace of Don; What's next?

By: JeffMasters, 7:41 PM GMT on July 30, 2011

Don is dead

Tropical Storm Don, the fourth named storm of the 2011 season, made landfall near Baffin Bay, Texas yesterday evening around 10pm CDT in less-than-grand fashion. The storm was looking very weak for the 24 hours before landfall, but fizzled rapidly after landfall, and by early Saturday morning, there was barely a trace of the storm to show that it even existed in the first place.

NHC Hurricane Specialist Eric Blake probably said it best in this mornings 5am EDT discussion on the storm:

THE DON IS DEAD. THE CYCLONE LITERALLY EVAPORATED OVER TEXAS ABOUT
AS FAST AS I HAVE EVER SEEN WITHOUT MOUNTAINS INVOLVED. DON HAS NO
CONVECTION...MEAGER RAINFALL...AND ONLY A SLIGHT SIGNATURE IN
SURFACE OBSERVATIONS AND RADAR DATA. THEREFORE...THIS IS THE LAST
ADVISORY ON THIS SYSTEM.


Figure 1. Total precipitation accumulation for the storm, estimated by radar.

The heaviest rainfall was falling south of the storm's center yesterday, so it wasn't surprising that Brownsville saw the most rain, 0.63 inches. KBRO also recorded 18 mph wind gusts. But to the north of the center, where many of the media were located, not a drop of rain fell. Corpus Christi saw zero inches of rain, but did record gale-force wind gusts (39 mph). Harlingen, near Baffin Bay, and close to where the center made landfall, saw 0.20 inches of rain and 18 mph wind gusts. This storm did very, very little to relieve any drought conditions in Southern Texas. And so it continues.

What's next: Invest 91L continues to impress

Invest 91L, which is located near 12°N 48°W in the central Atlantic, continues to impress today, and has shown signs of more organization over the past 24 hours. 91L will probably develop into a tropical cyclone before it reaches the Lesser Antilles, so residents of these islands should remain watchful and prepared. Satellite loops show not only organized thunderstorm activity, but also the makings of a surface circulation. Something this wave has working against it right now is dry air—there's a large mass of Saharan air on the north and east sides of the system, which could at least prevent significant intensification. Also, University of Wisconsin CIMSS analysis shows some strong wind shear (30-40 knots) to the north of the wave. However, I don't expect this to prevent development of the wave. Wind shear out ahead of the system is relatively low (5-15 knots). Moisture is plenty high within the system, and sea surface temperatures are warm and toasty (28°C+) and will only get warmer as 91L moves west into the Caribbean.


Figure 2. Infrared satellite of invest 91L taken at 1:15pm EDT today.

Forecast for 91L
Most of the reliable forecast models (GFS, CMC, FIM, and the ECMWF) have come to agree that 91L will develop, however, they differ on how long-lived that will be. Some of the models are suggesting it will be a short-lived tropical cyclone, not making it out of the Caribbean alive, and some suggest that it will hold together and intensify as it moves north of the Caribbean islands. The forecast track for the system will most likely be to the northwest through the Caribbean, at which point it will take a northeast turn near the Bahamas, never reaching the U.S. coast. HWRF agrees with this track (and also brings the system to category 2 strength by August 3rd). However, there is still some uncertainty that the system could track west, south of the Caribbean islands, and potentially into the Gulf of Mexico. However, none of the models that suggest this solution actually show that the wave will be a tropical cyclone at that point.

The National Hurricane Center is giving this wave an 80% chance of developing into at least Tropical Depression Five over the next 48 hours. Chances are we will see Emily out of this system. A Hurricane Hunter mission is scheduled for tomorrow at 2pm EDT, but I wouldn't be totally surprised to see them call this system this evening, given the threat to the Lesser Antilles.

Watching a northwest Caribbean disturbance

A broad area of disturbed weather is producing some heavy thunderstorms in the northwest Caribbean, southeast of the Yucatan Peninsula. Little to no low-level circulation exists with this feature, and none of the models are picking up on it. The Hurricane Center has "blobbed" this item (as I like to say) with a "near 0%" chance of developing over the next 48 hours. This disturbance could cause major flooding in the region given the amount of thunderstorm activity, and predictability for systems like this (potential Bay of Cempeche tropical cyclones) is very low. Models have a short lead time on development, and they spin up very fast once they enter the Bay of Campeche given the favorable topography of the land surrounding it. The difference between this system, though, and one like Arlene, is that there is very, very little low level circulation already present. Pre-Arlene was a bit more organized before it crossed the Yucatan, and so it's hard to imagine that this disturbance will be able to hold together, should it get that far.

If 91L develops, I'll be back tomorrow with a post.

Angela

Hurricane

Tropical Storm Don close to landfall; 91L tracks west

By: JeffMasters, 11:42 PM GMT on July 29, 2011

Tropical Storm Don continues to make its way west-northwest toward the Texas coast this evening. Don has increased steadily in pressure over the past 18 to 24 hours. Wind speed remained 45 knots in the 5pm EDT advisory. The strongest thunderstorm activity continues to be south of the center, southeast of Brownsville, Texas, but the strongest winds are to the north according to Hurricane Hunter data. A mesoscale vortex developed on the southern end this afternoon with high radar reflectivity. Radar estimated rainfall rates are as much as 5 inches per hour to the south, and around 2 inches on the north side of the storm, but these are likely an overestimate, although rainfall rate is definitely higher on the southern end of this storm. It began raining in Brownsville, Texas in the 2pm CDT hour, and so far the airport has received 0.3 inches of rain. The heaviest thunderstorms still look to be to Brownsville's southeast.


Figure 1. Radar reflectivity from Brownsville, Texas at 5pm CDT.

Forecast for Tropical Storm Don
A Hurricane Hunter is currently in the storm, and center fixes suggest Don will make landfall south of Baffin Bay, Texas, in the next couple of hours. Tropical storm-force winds, should there be any, will most likely be seen in a swath from Baffin Bay to Corpus Christi. Once Don moves inland it is expected to dissipate quickly, and without having produced enough meaningful rainfall to impact any drought conditions. The Hydrometeorological Prediction Center isn't predicting any rainfall that would exceed flash flood guidance, and no flood watches or warnings are in effect.

NHC Invest 91L

Moderate thunderstorm activity continues in Invest 91L this afternoon, and the Hurricane Center estimates that the axis of the wave is located near 42W. Estimates from satellites show that 91L has a moderate circulation at all levels, and the Advanced Scatterometer resolved a surface circulation early this morning.


Figure 2. Advanced Scatterometer pass over 91L at 7am EDT this morning. The wind barbs show a low-level circulation had formed near the most intense thunderstorms—a good sign of potential development.

Some of the reliable models—GFS, UKMET, and CMC—are developing 91L into at least a weak tropical cyclone. The ECMWF continues to show no development, but a more interesting solution, one that takes the wave on a southerly track. The GFDL does not develop Invest 91L, but the HWRF forecasts category 1 hurricane strength by August 1st. The track for 91L is likely a turn to the northwest when it reaches the Caribbean and a curve to the northeast around the Bahamas. The models that are developing the system do not suggest this is a U.S. landfall threat, although it's pretty early in the game to predict that, and I imagine the track will fluctuate over the next few days. Today the Hurricane Center gives the wave a 30% chance of development (now 50% in the 8pm EDT outlook) over the next 48 hours, and I'm around 40-50% over its lifetime.

I'll have a post tomorrow afternoon on the aftermath of Don as well as NHC Invest 91L.

Angela

Hurricane

Don closing in on Texas; 91L a potential threat to the Lesser Antilles

By: JeffMasters, 3:22 PM GMT on July 29, 2011

Tropical storm warnings are flying along the coast of Texas from Brownsville to Matagorda as Tropical Storm Don closes in on the Texas coast. Don remains a disorganized, moderate strength tropical storm, and appears unlikely to cause major damage or bring much-needed drought-busting rains to Texas. A hurricane hunter plane is in Don, and found highest surface winds of 55 mph at 11:06am EDT. Don continues to have trouble with moderate wind shear of 10 - 20 knots, which is injecting dry air to the northwest into the storm. Water vapor satellite images show this region of dry air to the northwest of Don. Visible satellite imagery from this morning shows little change to Don so far today, with most of the heavy thunderstorms on Don's south side, and the cloud pattern elongated, the sign of a storm struggling with wind shear. Radar out of Brownsville, Texas shows the main rain areas are on the south of Don's center, and bands of heavy rain are now very close to the Texas/Mexico border.


Figure 1. Morning image of Tropical Storm Don from the Brownsville, Texas radar.


Figure 2. The latest drought map for Texas shows that over 75% of the state is in exceptional drought--the highest category of drought. Image credit: U.S. Drought Monitor.

Forecast for Don
The wind shear and dry air affecting Don will continue until landfall, and it is unlikely Don will intensify to more than a 60 mph tropical storm. With most of the heavy thunderstorms displaced to the south side of the storm, Mexico will be the primary beneficiary of Don's expected rains of 3 - 5 inches. South Texas will see modest rains of 1 - 2 inches over a few isolated areas, but Don is going to do very little to bring drought relief to the state. Most of Don's rains in Texas will be concentrated in the extreme southern portion of the state near Brownsville. This portion of Texas is experiencing only moderate drought, and the extreme to exceptional drought areas of the state will miss the bulk of Don's rains.

For those of you wondering about your odds of experiencing tropical storm force winds, I recommend NHC's wind probability forecast. The 11 am version of this forecast shows that Corpus Christi Texas has the highest chance of tropical storm-force winds (39+ mph): 48%. The primary threat from Don will be heavy rain, which will caused localized flooding problems. An isolated tornado is also a possible concern.


Figure 3. Morning satellite image of 91L.

African wave 91L a potential threat to the Lesser Antilles
A well-organized African wave near 9°N 44°W (Invest 91L) is headed west-northwest at 15 - 20 mph, and could arrive in the vicinity of the Lesser Antilles Islands as early as Monday night. Residents of the Lesser Antilles should pay careful attention to this system, as it has the potential to organize into a tropical storm before reaching the islands. While visible satellite loops currently show only minimal heavy thunderstorm activity and no signs of a surface circulation, there is a pronounced large-scale rotation to the cloud pattern. Water vapor satellite loops show that a large area of dry air from Africa lies just to the north of 91L, and this dry air is inhibiting development. The SHIPS model is diagnosing low shear, 5 - 10 knots, over 91L, but the University of Wisconsin CIMSS analysis shows that moderate shear, 10 - 20 knots, is affecting 91L. Sea surface temperatures are 27.5° - 28°C, which is 1° above the 26.5°C threshold usually needed to support a tropical storm.

Forecast for 91L
Low to moderate wind shear of 5 - 15 knots is predicted along 91L's path over the coming three days, which should allow the storm to steadily organize, assuming it can shut out any incursions of dry air that might intrude. The latest 06Z run of the GFS model does show 91L developing into a tropical storm by Monday, but the other three most reliable models for forecasting formation of a tropical storm--the ECMWF, NOGAPS, and UKMET models--show little or no development of 91L in their latest runs. On Monday, when most of the models predict that squalls of rain from 91L will begin affecting the Lesser Antilles, wind shear is expected to rise to the moderate or high range, which should act to interfere with development. The latest runs of the GFDL and HWRF models show 91L developing into a hurricane by Monday, but these models are not to be trusted for systems that have not developed into a tropical depression yet. The long-range path of 91L could take it through the Caribbean or towards the U.S. East Coast; it is too early to know with path might be more probable. NHC is giving a 30% chance that 91L will develop into a tropical depression by Sunday morning.

Iran records its hottest temperature of all-time
Omidieh, Iran and Shoshtar, Iran hit a scorching 52.6°C (126.6°F) on July 27, the hottest temperatures ever recorded in the country. The previous record was 52.5°C (126.5°F) set in Hamidiyeh on August 4, 2001. If confirmed by the Iranian weather service, these readings would rank as the third hottest undisputed temperatures ever measured in Asia. There have been only two Asian readings matching or exceeding Wednesday's new Iranian record of 52.6°C that are undisputed that I am aware of. Both of these occurred last year, and were recognized by their respective country's meteorological services as new official records for their country:

53.5° (128.3°F) in Moenjodaro, Pakistan on May 26, 2010
52.6°C (126.7°F) in Abdaly, Kuwait on June 10, 2010

Iran is the third nation this year to set a new all-time heat record (no nations have set an all-time coldest temperature record this year, or did so in 2010.) The Democratic Republic of the Congo, the world's 12th largest country, set a new all-time extreme heat record on March 8, 2011, when the temperature hit 39.2°C (102.6°F) at M'Pouya. Congo's previous all-time hottest temperature was 39.0°C (102.2°F) at Impfondo on May 14, 2005.

Also this July, a 50.2°C temperature was measured at Aydyngkol Lake, China--the highest temperature on record at any official Chinese weather station. Next week, our weather historian, Christopher C. Burt, will report on this record. Credit for researching these records goes to weather records researcher Maximiliano Herrera, who maintains a comprehensive set of world extreme temperature records on his web site.

Vacation
I'm taking some time off today through August 9 for a family celebration and vacation, and don't plan on blogging again until August 10 unless a major hurricane develops. In my absence, Angela Fritz will be handling most of the blogging duties, and she will have a post on the latest for Don this afternoon. Angela is on Pacific time, so her posts will be later in the day than I make them.

Jeff Masters

Hurricane

Don battling dry air and wind shear

By: JeffMasters, 7:37 PM GMT on July 28, 2011

Tropical Storm Don continues to be an unimpressive low-end tropical storm as it continues northwest towards the Texas coast. Don formed yesterday afternoon from an African tropical wave that moved into the Gulf of Mexico under a region of low wind shear. Don's formation date of July 27 is nearly a month ahead of the usual August 23 date for the arrival of the season's fourth named storm of the year. There is currently no hurricane hunter airplane in Don, and a new airplane is not due in the storm until tonight. The last center fix at 1pm EDT found surface winds of 45 mph and a central pressure of 1005 mb, a 4 mb rise from earlier this morning. Water vapor satellite images show a region of dry air to the northwest of Don, over the western Gulf of Mexico. Wind shear as diagnosed by the University of Wisconsin CIMSS group and the SHIPS model show a moderate 5 - 15 knots of shear from strong upper level winds out of the north. This shear is creating problems for Don by injecting dry air into the system. Visible satellite imagery from early this afternoon showed the presence of surface arc-shaped clouds expanding outwards to the north from the center of Don. These type of clouds are a sign that the storm is struggling with dry air. When dry air at middle levels of the atmosphere gets injected into thunderstorms due to wind shear, the dry air tends to create strong downdrafts that rob the storm of moisture. These downdrafts spread out at the ocean surface and create arc-shaped surface cumulus clouds.


Figure 1. Visible satellite image of Don from pm EDT July 28, 2011, showing arc-shaped surface clouds--the tell-tale sign of dry air interfering with the storm's organization.


Figure 2. The latest drought map for Texas shows that over 75% of the state is in exceptional drought--the highest category of drought. Image credit: U.S. Drought Monitor.

Forecast for Don
The big question for Don is, will it bring significant rains to Texas? According to the National Climatic Data Center, the six-month period ending in June 2011 was the driest on record. Average rain between January and June was more than eight inches (203 millimeters) below average in Texas, and the state experienced record heat between April and June. The heat and lack of rain have brought exceptional drought--the highest category of drought--to over 75% of the state. Don has the potential to bring some decent drought-busting rains to the state. If Don can expand in size and intensify to a 50 - 55 mph tropical storm, it has the capability to bring hundreds of millions of dollars worth of beneficial rains to the state. We don't want Don to stay in its current state, which is too small and weak to bring significant rains to Texas. If Don follows the current NHC forecast, which brings the storm up to a moderate-strength tropical storm, that would be just right. Don's small size makes it prone to dry air and wind shear, though, and it is uncertain whether the storm can overcome these problems enough to become a significant rain maker. NHC gave Don a 12% chance of intensifying into a hurricane in the 11am advisory, which is a reasonable forecast, since Don is running out of time to get its act together in time to become a hurricane. None of the computer models is predicting Don will become a hurricane.

For those of you wondering about your odds of experiencing tropical storm force winds, I recommend NHC's wind probability forecast. The 11 am version of this forecast shows that Port O'Connor, Texas has the highest chance of tropical storm-force winds (39+ mph): 45%.

New hurricane archive search feature
The autocomplete entities in the wunderground search box has been extended to include hurricanes, so you can now search for a storm by name, year, or basin. Here are some examples in case you feel like exploring your new options:

By name:

Hurricane David - Atlantic, 1979
David, Major Hurricane - Atlantic, 1979
Major Hurricane David - Atlantic, 1979

By year:

2005 Hurricanes Atlantic
2007 Hurricanes Eastern Pacific

By basin:

Hurricanes Western Pacific 2011
Hurricanes Atlantic 2008

By category:

Tropical Storms Atlantic 2005
Tropical Depressions Indian Ocean 2011
Subtropical Storms Eastern Pacific 2010
Extratropical Storms Western Pacific 1988

I'll have a new post Friday morning.

Jeff Masters

Hurricane

Tropical Storm Don unimpressive so far

By: JeffMasters, 2:08 PM GMT on July 28, 2011

Tropical Storm Don formed yesterday from an African tropical wave that crossed into the Gulf of Mexico, and the thus-far unimpressive storm appears poised to bring tropical storm conditions to the lower Texas coast by Friday night. An Air Force Hurricane Hunter plane arrived in the center of Don around 8am EDT this morning, and has found Don to be a small tropical storm with top winds near 40 mph. The 7:57am EDT center fix found a central pressure of 1002 mb, which is 2 mb higher than NHC was estimating in its 8am EDT advisory. However, a pass through the center at 9:49am EDT found the pressure had dropped 2mb, to 1000 mb. Top reliable surface winds seen by the Air Force plane with its SFMR instrument as of 9:45am EDT were 41 mph, at 8:10 am EDT. Water vapor satellite images show a region of dry air to the northwest of Don, over the western Gulf of Mexico. Wind shear as diagnosed by the University of Wisconsin CIMSS group and the SHIPS model show a moderate 10 - 15 knots of wind shear. The shear is from strong upper level winds out of the north. Since the atmosphere to the north of Don is relatively moist, the moderate shear will not be as damaging to the storm as if these winds had been blowing from the northwest, where the driest air lies. Thus the shear direction is often just as important as the strength of the shear, and in Don's case, the shear direction should not force significant amounts of storm-disrupting dry air into the core. Water temperatures in the Gulf of Mexico are near 29°C, which is 2.5°C above the 26.5°C threshold typically needed to maintain a tropical storm.


Figure 1. Morning satellite image of Don.

Satellite imagery shows that Don is a very small storm. Thus, the storm is vulnerable to pockets of dry air and modest-sized jets of wind shear that we can't see from the relatively coarse-resolution data collected by surface stations, hurricane hunter flights, and satellites. The moderate wind shear over Don is keeping Don's circulation tilted so that the surface center is displaced from the center at higher levels. This tilt is keeping the storm from intensifying. Latest visible satellite loops show a modest increase in the intensity of the thunderstorm's near Don's center began at 9am EDT, but this could be a transient burst and not a sign the storm is undergoing intensification.


Figure 2. The latest drought map for Texas shows that over 75% of the state is in exceptional drought--the highest category of drought. Image credit: U.S. Drought Monitor.

Forecast for Don
The big question for Don is, will it be a boon or bane for Texas? The state is currently suffering through its worst drought in recorded history, and Don has the potential to bring some decent drought-busting rains to the state. If Don can expand in size and intensify to a 50 - 55 mph tropical storm, it has the capability to bring hundreds of millions of dollars worth of beneficial rains to the state. However, we have a Goldilocks problem. We can't have Don intensifying into a hurricane, or its winds and flooding might bring hundreds of millions in damage. Neither do we want Don to stay in its current state, which is too small and weak to bring significant rains to Texas. If Don follows the current NHC forecast, which brings the storm up to a moderate-strength tropical storm, that would be just right. This forecast is low-confidence, though, since Don's small size makes it prone to sudden changes in strength, either upward or downward. NHC is giving Don just a 14% chance of intensifying into a hurricane in its 5am advisory, but this could easily change upward if Don manages to overcome its vertical tilt and start consolidating an eyewall. I put the odds of Don reaching hurricane strength at 30%. None of the computer models is predicting Don will become a hurricane.

A small system like Don is relatively difficult to resolve in some of the computer models we use to forecast tropical storm track, and the forecast tracks of Don from these models have a higher spread than usual. For those of you wondering about your odds of experiencing tropical storm force winds, I recommend NHC's wind probability forecast, which is showing that Corpus Christi and Port O'Connor, Texas have the highest chance of 39+ mph winds: 40%.

I'll have a new post this afternoon.

Jeff Masters

Hurricane

Tropical Storm Don forms in the Gulf of Mexico

By: JeffMasters, 9:29 PM GMT on July 27, 2011

Tropical Storm Don, the fourth tropical cyclone of the 2011 season, has formed in the Gulf of Mexico just north of the Yucatan Peninsula. Hurricane Hunters began investigating the system earlier this afternoon and quickly found a closed surface circulation. As the mission continued to gather data from what was thought to be a tropical depression at the time, winds of around 39 mph were found, as well as a 1001 mb central pressure, bringing the system up to tropical storm strength.


Figure 1. Satellite loop of Tropical Storm Don. This loop will stay current.

The official forecast for Don agrees with what most of the models have been suggesting over the past 24 hours. Don will make its way toward the northwest over the next 48 hours before making landfall somewhere between Brownsville and Galveston. The statistical models tend to suggest a more southerly track toward Brownsville, and the dynamical models are forecasting anything from Corpus Christi to Galveston. They all tend to agree landfall will occur late on the 29th (Friday night). Whether or not Don will reach hurricane status is still in question. The Hurricane Center's initial forecast is that Don will remain a tropical storm until landfall. Today some models were intensifying Don to a strong tropical storm, but none crossed the hurricane threshold. Now that we have data from aircraft reconnaissance, the models will be able to get a better handle on potential intensity. The runs that occur later tonight and early tomorrow will have much less uncertainty than those from today.


Figure 2. Model forecast tracks for Tropical Storm Don as of Wednesday afternoon.

I believe Jeff will be back tomorrow for an update.

Angela

Hurricane

Drought continues; Yellowstone fires could become more frequent; 90L set to develop

By: JeffMasters, 3:58 PM GMT on July 27, 2011

Southern Drought Continues

Temperatures continue to soar into triple digits in the Southern Plains this week, and are expected to remain well above average for at least the next month. High air temperatures and low humidity (because of the low soil moisture) will continue to maintain drought conditions in the South unless we see some Gulf-landfalling tropical cyclones—a good remedy for a such an extreme drought.

This year's drought in the South is unprecedented by many definitions. Last year at this time, 0% of the contiguous U.S. was in exceptional drought. Last week, the exceptional drought region covered 11.96%. The area of contiguous U.S. in exceptional drought conditions has never been this high since the Drought Monitor record started in 2000. The highest it had been before June of this year was 7.85% in August of 2002.


Figure 1. Temperature anomaly (difference from average) in degrees Celsius for the period July 1 through July 25 (top) and soil moisture anomaly in millimeters (bottom) on July 25 (from the Climate Prediction Center).

In late June, the U.S. Department of Agriculture designated 213 counties in Texas (84% of the state) as primary natural disaster areas. As I mentioned yesterday, the Texas drought and wildfires are one of the nine billion-dollar disasters of 2011 so far. The National Climatic Data Center estimated that this event had cost up to $3 billion as of June 16. This number is surely rising every day that the South doesn't see rain.

New study concludes Yellowstone wildfires could become more frequent

In a study published this week by the Proceedings of the National Academy of Sciences, researchers have concluded that global warming could have a serious impact on the severity and frequency of wildfires in the Yellowstone region (an area where the states of Montana, Idaho, and Wyoming come together). Historically in this region, fewer than 5% of wildfire occurrences account for 95% of the total area burned. But in a global warming scenario, they found that fire activity could become more severe and more frequent, causing the ecosystem to change dramatically.

Using climate conditions and historical fire data from 1972 to 1999, it was possible to link certain environmental thresholds (temperature, humidity, etc) to past wildfire events. Then by employing the output of various climate models, fire frequency can be forecast well into the future. Figure 2 illustrates the result from one of the climate models they used in the study, and the upward trend of fire activity over the next 100 years. In 1988, a particularly hot and dry year, 36% of the park burned. The study uses this year as a baseline to compare future events.


Figure 2. Figure 2B from the manuscript. Observed burn area (blue line) median of predicted area burned (black dotted line), and ranges (light and dark orange) aggregated over the Yellowstone area defined by the study by Westerling et al. (Source).

What was once a low-probability event could become a high-probability event by mid-century. Fires that have only happened every 100 to 300 years in the past could now be occurring every 30 years in the future. The results of this research has implications for sub-alpine forests across the globe. Warming temperatures and decreasing humidity will lead to more wildfires, and will cost billions of dollars to fight them, if we choose to do so.

Invest 90L

90L has moved west overnight and looks ripe to develop today. While the upper level circulation (500 mb) is very much displaced, the lower level circulation looks strong and coherent through the system's mid-levels (850 and 700 mb). Thunderstorm activity continues to organize, and it appears that a surface circulation is developing. Moisture remains high in the system (around 4.5 g/kg specific humidity) and wind shear should be somewhat favorable as it crosses through the Gulf of Mexico. In terms of track, the statistical models have generally been favoring a Brownsville landfall scenario, but the dynamical models have been inching north over the past day or so. The HWRF is in line with the ECMWF deterministic today, with landfall near Corpus Christi.



The Hurricane Hunters have a mission scheduled for 18Z today (2pm EDT) to investigate whether or not 90L has a closed surface circulation. If it does, given the amount of organized convection and moderate wind speeds (around 34 mph in the latest invest update), the Hurricane Center will probably call this system at least Tropical Depression Four.

If 90L develops this afternoon, I will have another update to look at track and intensity forecasts.

Angela

Drought Fire Hurricane

The nine billion-dollar weather disasters of 2011 (so far); Invest 90L rises again

By: angelafritz , 4:12 PM GMT on July 26, 2011

It's been an unprecedented year for weather disasters in the United States, with the dangerous portion of hurricane season still to come. We've already seen nine billion-dollar weather disasters so far in 2011. The National Climatic Data Center (NCDC) June disaster report estimates that, through May, 2011 is the costliest year since they began tracking billion-dollar disasters in 1980. The cost of the disasters through May could be as high as $32 billion, compared to a typical year-to-date cost of $6 billion. 2011 to-date now ties the entire year of 2008 for the most billion-dollar weather disasters in one year. Of course, this number could go up if we see some hurricane landfalls this year.

Here are NCDC's estimates of the top-end damages from 2011's billion-dollar weather disasters so far:



Missouri River Flooding
Snowfall was abnormally heavy in the Rocky Mountains of Montana and Wyoming this past winter (over 200% of average), and record rains fell over the Upper Midwest this Spring, the effects of which continue to be felt along the Missouri River. In May, the Army Corps of engineers began releasing a record amount of water through the dams above Gavins Point, including the Garrison Dam in Central North Dakota. The flooding has kept many bridges closed, making it impossible to cross the river for a hundred miles at a time in some places.

Texas Drought & Wildfires
Texas is in the midst of one of the worst droughts of its history. As of June 28, 2011, 91% of Texas was in extreme or greater drought, and 47% of the state was in an "exceptional drought," the most severe category. In April and May of 2011, wildfires burned over 3 million acres across the state. The governor of Texas, Rick Perry, has declared a State of Disaster every month since December 2010. As of June 16, NCDC estimates that the drought and fires in Texas have cost $3.0 billion—an amount that is likely to rise as the event continues.

Mississippi River Flooding
Between the spring snow-melt and two storms that dumped massive amounts of rain in the Mississippi watershed in April, the Mississippi was in for a flood of record proportions. The river began to bulge by the beginning of May, flooding every state from Illinois to Louisiana and Mississippi. A federal disaster was declared by the President in Kentucky, Tennessee, and Mississippi. In an effort to save Baton Rouge and New Orleans, Louisiana, the Army Corps of Engineers opened the Morganza Spillway on May 14, which flooded 4,600 square miles of Louisiana. The NCDC estimates $4 billion in damages from this flood, although the final amount might not be fully realized yet.

Mississippi River Flood 2011 Memphis
An overflowing Mississippi River at Memphis, Tennessee on May 8, 2011.

Midwest/Southeast Tornado Outbreak (May 22-27)
This six-day tornado outbreak killed approximately 180 people, and includes the EF-5 tornadoes that rolled through Joplin, Missouri on May 22, and El Reno, Oklahoma on May 24. Tornadoes in this storm were spawned from central Texas to the Upper Midwest. The whole event is estimated to have done $7 billion in damages.

2011 Super Outbreak (April 25-30)
Most of the tornadoes spawned in this storm happened in the Southeast, from Mississippi to Virginia, though a total of 334 tornadoes have been confirmed in 21 states from Texas to New York. April 27th, in particular, was a notably destructive and deadly day, as 188 tornadoes touched down in the Southeast, four of which were rated EF-5. The NCDC estimates that the Super Outbreak resulted in at least $5.5 billion in damages.

Mississippi River Flood 2011 Memphis
Just a portion of the aftermath from the EF-4 tornado that devastated Tuscaloosa, Alabama
on April 27, 2011. Image credit: Wikipedia

Midwest/Southeast Tornado Outbreak (April 14-16)
This storm generated at least 200 tornadoes across 16 states in mid-April, leading to 38 deaths. The system moved quickly from the Plains to the Mid-Atlantic, where the most notable tornado of the outbreak occurred near Raleigh, North Carolina. This tornado was rain-wrapped as it headed in the direction of Raleigh, and was later rated an EF-3. The NCDC estimates that this outbreak resulted in $2 billion in damages.

Southeast/Midwest Severe Storms (April 8-11)
Tornadoes were reported in Virginia and Iowa from April 8-11. A significant day of severe weather occurred on April 9th, as a powerful storm over the Upper Midwest spawned tornadoes in Iowa. The strongest of these tornadoes was the huge, 3/4 mile-wide tornado that plowed through the tiny town of Mapleton, Iowa on Saturday evening, leaving a trail of destruction 3.5 miles long. The tornado, preliminarily rated as an EF-3 with 136 - 165 mph winds, flattened 20% of the town of 1200 residents and damaged half of the buildings. The NCDC estimates that this weekend of severe weather caused $2.2 billion in damages.

Midwest/Southeast Severe Storms (April 4-5)
Damaging straight-line winds and tornadoes were spawned by a storm that pushed through the central U.S. in early April. Power outages were extensive across the southern and eastern U.S., and many people were killed by falling trees and branches. Tornadoes touched down in Arkansas, Kentucky, and Mississippi. 1,318 reports of damaging wind were submitted to local Weather Service offices on April 4th alone. The NCDC estimates that this tornado and wind event caused $2 billion in damages.

Groundhog Day Blizzard of 2011
This storm stretched from northeast Mexico to Canada, but is most memorable for its effect on Chicago, where 1-2 feet of snow fell, combined with winds over 60 mph which led to blizzard conditions. 21.2 inches of snow fell at Chicago O'Hare International Airport, making it the third largest snowfall total in Chicago history. Blizzard conditions were reported in many other large cities during the storm's lifetime, including Oklahoma City, St. Louis, Detroit, Cleveland, and New York. This storm also brought ice and wintry mix as far south as Albuquerque, Dallas, and Houston. At least 36 deaths were caused by this storm, most of which were vehicle-related. NCDC estimates this storm did at least $3.9 billion in damage.

Chicago Blizzard 2011
The Windy City on February 1, 2011 during the Groundhog Day Blizzard.

NHC Invest 90L, Born Again

Invest 90L spiked in thunderstorm activity and circulation yesterday, leading NHC to re-invest the system. 90L is still south of Cuba moving ever-so-slowly to the west. While low level (850mb) circulation has increased since yesterday morning, the system is tilted southeast with height. This is likely due to the westerly wind shear it's facing right now. As the system moves into the Gulf, shear will become more favorable (if there's shear present, easterly is better than westerly). The wave is still moist and moisture is expected to remain high (4 to 5.5 g/kg specific humidity) as it tracks into the Gulf of Mexico.



Again this morning, none of the models are suggesting meaningful development of Invest 90L. However, the GFS (finally) has come around to resolving the circulation at all. Dr. Rob Carver and I spoke this morning, and we came to the conclusion that the lack of observations in this region, combined with the small size of the system, is causing the models to not have the best handle on the situation. The Hurricane Center has a Hurricane Hunter mission scheduled for 18z (2pm EDT) tomorrow, after which we could see the models starting to favor development again. Today the Hurricane Center is forecasting a 20% chance of development over the next 48 hours. I agree with that, but I also think that beyond 48 hours this wave is going to have a better shot at developing a closed circulation at the surface.

Angela

Climate Change Drought Flood Fire Tornado

A heat wave recap; generally quiet tropics

By: JeffMasters, 4:45 PM GMT on July 25, 2011

Last week's U.S. heat wave has finally subsided, and most of the Northeast will see some cool highs in the 70s today. Unfortunately, the Midwest, and mid-Atlantic will continue to see high temperatures in the 90s for the rest of this week, and the southern Plains will be forced to continue to endure triple-digits.

According to the National Climatic Data Center (NCDC), 2,100 daily high maximum temperature records have been set so far in July 2011, and 51% of those were set last week. 4,734 daily high minimum temperature records have been set so far this month, and 55% of those were set last week. Here's a breakdown of last week's records for the period July 18 through July 24:

High Maximum:

• 1,076 warmest maximum temperature for the date
• 90 warmest maximum temperature for the month of July
• 56 warmest maximum temperature of all time

High Minimum:

• 2,595 warmest minimum temperature for the date
• 207 warmest minimum temperature for the month of July
• 123 warmest minimum temperature of all time

The number of warm minimum temperatures is especially disturbing, as these tend to have more of an impact on health than the high maximums. When the temperature remains high at night, it prevents the body from being able to recover from the day's heat. According to NOAA, from July 1 through July 19, there were 22 heat-related deaths in the United States. Reuters is reporting that 34 deaths resulted from this heat wave. In an average year, heat remains the number one weather-related killer in this country. In some ways, the overnight low temperatures are the best way to quantify a heat wave, possibly even better than the heat index.


Figure 1. Map of daily high maximum temperature records for the period July 1 through July 25 from NCDC. Red circles without an X denote a broken record; red circles with an X denote a tied record.

Tropical Overview

The wave formerly known as Invest 90L

The wave formerly known as Invest 90L is moving slowly west through the Caribbean near Jamaica. A new burst of convection started this morning, which will undoubtedly produce some heavy rain over southern Cuba and Jamaica. While low-level circulation has remained about the same since late last week, the wave has become top-heavy with increased circulation at higher levels (700-500mb). None of the models (GFS, ECMWF, CMC, NGPS, UKMET) are developing this wave as tracks into the Gulf of Mexico, and they're all in agreement that the path will be toward far southern Texas or northern Mexico, except for the ECMWF deterministic run, which hints that it will take a turn toward the northern Gulf. However, this model hasn't shown actual development from the wave since Tuesday or Wednesday of last week.

NHC has dropped this invest as of Saturday afternoon, but it remains on their radar. They're giving the wave a 0% chance to form over the next 48 hours. Given the recent uptick in mid-level circulation, I'd imagine they're still a little concerned about the potential for this wave to fire-up again once it's in the Gulf, and it will surely be of concern for Cuba as it tracks westward. However, given the lack of model support for almost 7 days in a row now, I'd say this wave has seen its glory come and go.


Figure 2. Visible tropical Atlantic satellite captured at 11:14am EDT on Monday.

Other North Atlantic waves

There are a couple other waves to speak of that have left the coast of Africa in the past few days, one located near 40W and the other closer to Africa, around 30W, which is tangled up in the monsoon trough. The former is expected to take a southerly track, skirting northern South America, and possibly into the Bay of Campeche. Given this track, none of the models are suggesting it will develop. However, tropical cyclones that spin up in the Bay of Campeche generally have a short forecast lead time, so it's something to watch. The latter wave could take a slightly more northern track through the Caribbean islands, and a couple of the models seem to favor this wave for development at the end of their runs.

Tropical wave activity has been lacking so far this season, but climatologically we should see an increase in African easterly waves in August and September.

Angela

Hurricane Heat

July 22, 2011: A day of records

By: JeffMasters, 4:56 PM GMT on July 23, 2011

The crest of the extreme heat wave of July 2011 has passed, although temperatures are still going to be dangerously hot in the Mid-Atlantic and Northeast today. New York City (Central Park) will reach 100° again, as well as Philadelphia and possibly Washington Dulles. Heat index values could surpass the 110° mark today, and excessive heat warnings are in effect from New York City to South Carolina, as well as a large portion of the Central United States. Yesterday, the heat index soared past 120° in Wilmington, DE (124), Easton, MD (125), Annapolis, MD (120) and Atlantic City, NJ (122), among others. A more complete list of Friday's heat index extremes can be found here.

Numerous records fell yesterday as far north as Maine. There were plenty of daily records to talk about, but here are some of the noteworthy all-time record high temperatures:

Newark, NJ: 108° (old record was 105° set in 2001)
Washington Dulles, DC: 105° (old record was 104° on multiple dates)
Bridgeport, CT: 103° (ties the old record set in 1957)
Hartford, CT: 103° (old record was 102° set on multiple dates)
New Haven, CT: 102° (old record was 101° set in 1926)

Baltimore hit 106°, one degree shy of their all-time high record which was set in 1936. New York City (Central Park) set a daily record of 104°, which was 2 degrees shy of their 106° all-time high record, which was also set in 1936. More on the record-setting year of 1936 in yesterday's blog from Jeff. Two notable all-time record high minimums were also set yesterday: 84° in New York (Central Park) and 86° in Newark, NJ.

Our weather historian, Christopher C. Burt, keeps track of 303 select stations in the U.S. with long standing record histories. So far this summer, seven of these have broken or tied their all-time maximum temperature records. Some of these were long-standing:

• Amarillo, TX 111° (1892)
• Dodge City, KS 110° (1874 tied)
• Newark, NJ 108° (1893)
• D.C. Dulles 105° (1962)
• Tallahassee, Fl 105° (1883)
• Hartford, CT 103° (1885)
• New Haven, CT 102° (1780)

The last summer to have more all-time high records than this year was 2002, which set 9. Christopher C. Burt estimates that yesterday probably rates in the top five hottest days on record for the mid-Atlantic states (Washington D.C. to Boston).

Invest 90L


Satellite imagery of NHC Invest 90L this morning.

Invest 90L is looking ragged on satellite as it makes its way across the Caribbean islands. While this wave looked ripe for eventual development earlier this week, it has really taken a turn for the worse as it moved across the Main Development Region of the North Atlantic. Today, low level circulation is could favorably be described as less than moderate, and almost nonexistent at higher levels. Today, not one of the global models I've looked at (ECMWF, NOGAPS, CMC, UKMET, or GFS) develop 90L, but they are coming into better agreement that the wave's track will be across the Caribbean islands and into the Gulf of Mexico, rather than up the east coast of Florida. This could be one of the reasons the models are not suggesting development—too much land interaction, not enough time over open warm waters. However, its hard to say that this wave will not show some signs of improvement when it reaches the Gulf. Water will be toasty, moisture will be relatively high, and wind shear will remain incredibly low. Today the National Hurricane Center is giving this wave a 20% chance of development over the next 48 hours. My forecast has been the same for the past two days, right around 20% chance of development over the lifetime of the wave.

Thanks to our weather historian Christopher C. Burt for some useful information on heat waves and yesterday's records. I'll have another blog on Monday.

Angela

Heat

Intense heat wave bakes the Eastern U.S.

By: JeffMasters, 3:27 PM GMT on July 22, 2011

Intense heat seared large sections of the U.S. on Thursday, with dozens of new daily high temperature records adding to the formidable number of new records piling up this week. On Wednesday, 140 daily maximum temperature records were tied or broken, according to NOAA's National Climatic Data Center. This represents over 2.4% of all stations in the U.S., which is an exceptionally high number of records for one day. Over the past 30 days, daily high temperature records have outpaced low temperature records by more than 4 to 1, 1859 to 453, and by almost three to one over the past year. Daily high temperature records set yesterday included 100° at Detroit, the first time in sixteen years that city has seen the century mark. Two hyperthermia deaths were reported in the Detroit area, bringing the heat wave death toll for the U.S. to 24 for the week. Newark, NJ hit 103°, just 2° below that city's all-time record hottest temperature of 105°. That record may be challenged today, as the temperature in Newark at 11am was already 100°. Other notable temperatures yesterday included 101° in Syracuse, NY, only 1° below that city's all-time high of 102°; 95° in Binghamton, NY, 3° below their all-time high; 102° in Toledo, 3° below their all-time high; 102° in Raleigh, 3° below that city's all-time high of 105°. Accompanying the heat was high levels of air pollution, which also contributes to mortality. Air pollution reached code red, "Unhealthy", in Gary Indiana yesterday, and was code orange, "Unhealthy for Sensitive Groups" in thirteen other states.

The blast furnace-like conditions will continue today across much of New England and the mid-Atlantic, where high temperatures are expected to climb above 100° in Washington D.C., Baltimore, and New York City. Air pollution is expected to exceed federal standards and reach code orange, "Unhealthy for Sensitive Groups", in at least 18 states today, according to the latest forecasts from EPA. The pollution will be worst in Washington D.C. and Baltimore, where "code red" conditions--"Unhealthy"--are expected. The heat will continue in the mid-Atlantic states through Sunday, then ease on Monday when a cold front is expected to move through.


Figure 1. July temperatures in the lower 48 states between 1895 - 2010 showed a warming of about 1.2°F (red line) during that time period. The warmest July on record was 1936, with an average temperature of 3.1°F above average. The year 2006 was a close second, just 0.1°F behind. If model projections of an increase in U.S. temperature of 4 - 6.5°F by 2100 are correct, an average July in 2050 will have temperatures warmer than the record warm temperatures of 1936. Image credit: NOAA/NCDC.

The summer of 2011's place in history
July 2011 is on pace to be one of the five hottest months in U.S. history, but may have a tough time surpassing the hottest month of all time, July 1936. In that year, the dry soils of the Midwest's Dust Bowl helped create the most extreme heat wave in U.S. history during July. Wunderground's weather historian, Christopher C. Burt, has a look back at this great heat wave in his current post. I expect that by the time July 2011 is done, it will be a top-five warmest July on record, but will not surpass July of 1936 or July of 2006 (which holds second place, just 0.1° cooler than July 1936.) The summer of 1936 was also the hottest summer in U.S. history. That mark will also be tough to surpass this year, since June 2011 was the 26th warmest June on record, and June 1936 was the 11th warmest. August 1936 was the 4th warmest August on record. At this point, there's no telling how warm August 2011 will be, though NOAA's Climate Prediction Center is forecasting a much above average chance of warmer than average conditions over 95% of the contiguous U.S for the first week of August.


Figure 2. The 8 - 14 day outlook from NOAA's Climate Prediction Center predicts much above average chances of warmer than normal temperatures during the last few days of July and the first four days of August.

Climate change and U.S. heat waves
The heat index--how hot the air feels when factoring in both the temperature and the humidity--has been exceptionally high during this week's heat wave, due to the presence of very high amounts of water vapor in the atmosphere. That has made this heat wave a very dangerous one, since the body is much less able to cool itself when the humidity is high. The high humidities in the Midwest were due, in great part, to the record rains and flooding over the past few months that have saturated soils and left farmlands flooded. Today's extreme heat index values over the mid-Altantic are due, in large part, to near record warm ocean temperatures off the mid-Atlantic coast. According to the UK's HADSST2 data set, sea surface temperatures between 35° - 40°N and 75 ° - 70°W, along the coast from North Carolina to New Jersey, were 5.4°F (3.0°C) above average during June 2011. This is the warmest such temperature difference for any month in the historical record, going back to the 1800s. The most recent sea surface temperature anomaly maps from NOAA show that the July ocean temperatures have not been quite as extreme, but ocean temperatures in this region during July have averaged nearly 2°C above average, the second highest July ocean temperatures on record, behind 2010.

During the 1930s, there was a high frequency of heat waves due to high daytime temperatures resulting in large part from an extended multi-year period of intense drought. By contrast, in the past 3 to 4 decades, there has been an increasing trend in high-humidity heat waves, which are characterized by the persistence of extremely high nighttime temperatures. In particular, Gaffen and Ross (1999) found that summer nighttime moisture levels increased by 2 - 4% per decade for every region of the contiguous U.S. between 1961 - 1995. Hot and humid conditions at night for a multi-day period are highly correlated with heat stress mortality during heat waves.

Not surprisingly, the frequency, intensity, and humidity of heat waves is expected to increase dramatically in coming decades, if the forecasts of a warmer world due to global warming come true. A study presented in the U.S. Global Change Program Impacts Report, 2009, predicted that by 2080 - 2099, a heat wave that has a 1-in-20 chance of occurring in today's climate will occur every 2 - 3 years over 95% of the contiguous U.S. (Figure 3.) I estimate that this week's U.S. heat wave has been a 1-in-5 to 1-in-20 year event for most locations affected, so heat waves like this week's will be a routine occurrence, nearly every year, by the end of the century. According to a study published by scientists at Stanford University last month, though, this may be too optimistic. In their press release, lead author Noah Diffenbaugh said, "According to our projections, large areas of the globe are likely to warm up so quickly that, by the middle of this century, even the coolest summers will be hotter than the hottest summers of the past 50 years."


Figure 3. Simulations for 2080-2099 indicate how currently rare extremes (a 1-in-20-year event) are projected to become more commonplace. A day so hot that it is currently experienced once every 20 years would occur every other year or more frequently by the end of the century under the higher emissions scenario. Image credit: U.S. Global Change Program Impacts Report, 2009.

Arctic sea ice continues its record retreat
Sea ice in the Arctic continues to melt at the fastest pace in recorded history, as July ice extent has been averaging 5 - 10% less than the record low values set in 2007. According to the July 18 update from the National Snow and Ice Data Center, the rapid decline in the past few weeks is related to persistent above-average temperatures, and an early onset of the melting season due to especially low snow cover in Europe and Asia during May and June. High pressure and clear skies have dominated in the Arctic this summer, but that pattern is changing. The latest 2-week forecast from the GFS model shows that low pressure will dominate the Arctic for the next two weeks, bringing cloudier skies and less melting. This will likely slow down the melting enough so that sea ice loss will no longer be on a record pace by the 2nd week of August.

Tropical Storm Cindy
Tropical Storm Bret is dead, and Tropical Storm Cindy is moving over very chilly waters of 20°C, and does not have long to live. Cindy is not a threat to any land areas.

Invest 90L: an African wave worth watching
An African wave (Invest 90L) near 14N 55W, 400 miles east of the Lesser Antilles Islands, is moving west-northwest at about 15 - 20 mph. This wave is generating a limited amount of heavy thunderstorms due to the presence of a large amount of dust and dry air from the Sahara, and will spread heavy rain showers and strong gusty winds to the northern Lesser Antilles tonight through Saturday. The wave has a modest degree of spin to it, and is under low wind shear, 5 - 10 knots.

Dry air will continue to be a problem for 90L through Sunday, but once it finds a moister environment near the Bahama Islands early next week, it could develop. However, the expected track of the disturbance takes it over the rugged terrain of Hispaniola, which would inhibit development. Furthermore, wind shear is expected to rise to the moderate range, 10 - 20 knots, on Saturday, and could increase further by Monday, according to most of the computer models. Of the latest 00Z and 06Z runs of the four reliable models for predicting formation of a tropical depression, only the NOGAPS model shows development of 90L. The NOGAPS predicts the wave could attain tropical depression status on Tuesday, over the northwestern Bahama Islands just off the coast of Southeast Florida. The other models generally depict too much wind shear for the wave to develop. Right now, the deck appears stacked against development for 90L through at least Monday. NHC is predicting a 20% chance of development by Sunday. The eventual track of 90L next week has been trending more to the south in recent model runs, as they are generally depicting a weaker trough of low pressure developing over the Eastern U.S. This reduces the chances 90L will move up the U.S. East Coast, and increases the chances that it will enter the Gulf of Mexico.


Figure 4. Satellite image of Hurricane Dora taken July 20, 2011 by NASA's Aqua satellite.

Hurricane Dora in the Eastern Pacific weakening
Hurricane Dora in the Eastern Pacific put on an impressive burst of intensification yesterday, topping out as an impressive Category 4 storm with 155 mph winds, just 1 mph short of Category 5 status. However, high wind shear acted to knock a hole in Dora's eyewall, which has now collapsed, and steady weakening of the storm will occur today. Dora is expected to move parallel to the coast of Mexico, and should not cause any major trouble in that country. Dora is the second major hurricane in the East Pacific this year; Hurricane Adrian topped out as a Category 4 storm with 140 mph winds in early June. A NOAA P-3 aircraft will be investigating Dora over the next few days, to learn more about how Eastern Pacific hurricanes weaken when they move over colder water.

Vacation
This will be my last post until Thursday, unless 90L gets far more interesting than the current forecast. I'm headed up north to Lake Michigan to cool off and relax for a few days. In my absence, Angela Fritz will be handling the blogging duties, and she will have a post on the latest forecast for 90L on Saturday. Angela is on Pacific time, so her posts will be later in the day than I make them.

Jeff Masters

Heat

U.S. heat wave blamed for 22 deaths; Bret and Cindy no threat

By: JeffMasters, 3:07 PM GMT on July 21, 2011

The dangerous U.S. heat wave of July 2011 will continue to bring another day of exceptionally humid heat to over 100 million Americans today, with 33 states plus the District of Columbia currently under heat advisories. The heat index--how hot the air feels when factoring in both the temperature and the humidity--exceeded 100° in twenty states in the Central and Eastern U.S. on Wednesday, peaking at 123° in Council Bluffs, Iowa. At least 22 deaths are being blamed on the heat in the Midwest. The extreme humidity that has accompanied this heat has made it a very dangerous one, since the body is much less able to cool itself when the humidity is high. The high humidities are due, in great part, to the record rains and flooding in the Midwest over the past few months that have saturated soils and left farmlands flooded. Accompanying the heat has been high levels of air pollution, which also contributes to mortality. Air pollution is expected exceed federal standards and reach code orange, "Unhealthy for Sensitive Groups", in at least 22 states today, according to the latest forecasts from EPA.

The extreme heat peaked in Chicago yesterday, where the temperature hit 100° at Midway Airport and the Chicago Lakefront station. Rockford, Illinois hit 100°, the first time in 22 years that city had seen 100° temperatures. Detroit is expected to hit 100° for the first time in sixteen years today, and I think I'm going to skip the Ann Arbor Art Fair! New York City and the mid-Atlantic states are expected to be near 100° on Friday. The forecast high of 103° in Washington D.C. for Friday is just 3° below the hottest temperature ever recorded in the city, 106°. The heat will continue in the mid-Atlantic states through Sunday, then ease on Monday when a cold front is expected to pass through. Wunderground's climate change blogger Dr. Ricky Rood has some good insights on the current heat wave in his latest post. A few notable highlights from this week:

Omaha, Nebraska has been above 80° for a four-day period beginning on July 17. This is the 2nd longest such stretch on record, next to the 8-day period that ended July 25, 1934. Multi-day periods when the low temperatures do not cool off below 75° are associated with high heat wave death rates.

Amarillo, Texas recorded its 26th day of 100° temperatures yesterday, tying the city's record for most 100° days in a year, last set in 1953. Record keeping in the city goes back to 1892.

Minneapolis, Minnesota, recorded its highest dew point ever, 82°, on Tuesday. The heat index hit a remarkable 118° in the city, which tied July 11, 1966 for the highest heat index on record in the city. Minnesota's all-time highest dew point temperature of 86° was tied on Sunday, in Madison. The previous record was in St. James and Pipestone in July of 2005.

The latest National Weather Service storm summary has a list of cities where the heat index exceeded 100° yesterday.


Figure 1. On Wednesday, heat advisories for this dangerous heat wave covered portions of 33 states plus the District of Columbia, an area with 141 million people--about half the population of the U.S.

Tropical Storm Bret no threat
Tropical Storm Bret continues to struggle with high wind shear of 20 - 30 knots, and high shear is expected to affect the storm the remainder of the week. The combination of high wind shear and dry air nearby should act to destroy Bret by Sunday, and the storm is not a threat to any land areas.

Tropical Storm Cindy forms
Tropical Storm Cindy formed yesterday 600 miles to the east of Bermuda. Cindy's formation was 24 days ahead of the usual formation date for the third named storm of the Atlantic hurricane season, which is August 13. This year has the most early season activity since 2008, when Hurricane Dolly got named on July 20. Wind shear is a moderate 10 - 20 knots, and is expected to remain moderate for several days. However, Cindy has moved over cool ocean waters of 25°C this morning, and this temperature is 1.5°C below the threshold of 26.5°C that tropical storms typically need in order to maintain their strength. With Cindy predicted to move over waters of just 21°C by Friday morning, the storm doesn't have long to live. Cindy is not a threat to any land areas.

An African wave worth watching
An African wave near 12N 50W, 700 miles east of the Lesser Antilles Islands, is moving west to west-northwest at about 15 mph, and is generating a limited amount of heavy thunderstorms due to the presence of a large amount of dust and dry air from the Sahara. This wave will spread heavy rain showers and strong gusty winds to the northern Lesser Antilles beginning on Saturday. The wave has a modest degree of spin to it, and is under low wind shear, 5 - 10 knots. Once it finds a moister environment near the Bahama Islands early next week, it could develop. Of the latest 00Z and 06Z runs of the four reliable models for predicting formation of a tropical depression, only the NOGAPS model shows development of the wave. The NOGAPS predicts the wave could attain tropical depression status on Wednesday, just off the coast of South Carolina. The other models generally depict too much wind shear over the Bahamas for the wave to develop. The eventual track of the wave once it reaches the Bahamas early next week is uncertain; there will be a trough of low pressure located off the U.S. East Coast that will be capable of turning the wave to the north, along the East Coast. However, it is also quite possible that the wave would be too weak and to far south to feel the influence of this trough, and instead would enter the Gulf of Mexico.


Figure 2. Morning satellite image of Hurricane Dora.

Hurricane Dora in the Eastern Pacific close to Category 5
Hurricane Dora in the Eastern Pacific put on an impressive burst of intensification over the past 24 hours, and is now a very impressive Category 4 storm with 155 mph winds, just 1 mph short of Category 5 status. Dora is expected to move parallel to the coast of Mexico, and should not cause any major trouble in that country. Dora is the second major hurricane in the East Pacific this year; Hurricane Adrian topped out as a Category 4 storm with 140 mph winds in early June.

Think cold. Way cold!
Those of us sweltering in today's heat would do well to consider that on this date in 1983, Vostok, Antarctica shivered at -128°F--the coldest temperature ever measured on Earth. The low tonight in Vostok is expected to be a relatively balmy -80°F.

Jeff Masters

Heat

Famine declared due to drought in Somalia; U.S. heat wave shifts east

By: JeffMasters, 3:43 PM GMT on July 20, 2011

The main rainy season rains have failed again in the Horn of Africa--the region of East Africa comprising Somalia, Kenya, and Ethiopia. Rainfall over most of the Horn of Africa between February and July 2011 was 2 - 8 inches (50 - 200 mm) below average, leading to today's official declaration that famine conditions now exist. The region is experiencing a humanitarian emergency with more than 2 million malnourished children needing lifesaving action. The Horn of Africa has two rainy seasons, a main rainy season in April/May, and then the "short rains" of October/November. The main 2010 April/May rainy season brought above average rains to the region. However, the October/November 2010 "short rains" failed, as did the April/May 2011 main rainy season rains. The failure of two consecutive rainy seasons is a devastating blow for East Africa. African countries are highly dependent on rain-fed agriculture for both employment and economic production, with agriculture accounting for more than 50% of gross domestic product and up to 90% of employment across much of the continent (World Development Indicators 2009, World Bank). One third of the population of Africa lives in drought-prone areas (World Water Forum, 2000), and about 25% of the population of Africa currently experiences high water stress. Remarkably, several nations in East Africa have been selling their land to other countries to raise food for export in recent years. These nations include Ethiopia and Sudan, who both receive massive food aid from the U.N. World Food Program. According to the fascinating and sobering book, World on the Edge by Lester Brown, in January 2009, Saudi Arabia celebrated the arrival of the first shipment of rice on land they had acquired in Ethiopia, where the World Food Program was feeding 5 million people at the time. Saudi Arabia has been actively buying land in other countries to raise crops since the recent failure of agriculture in their country after they pumped their aquifers dry. India, South Korea, and Saudi Arabia have all brought land to grow crops in Sudan, which was the site of the World Food Program's largest famine relief effort in 2010. The world is running short of food, and nations that cannot feed themselves are aggressively competing to buy land to grow food where land costs are low, like East Africa.


Figure 1. Rainfall over most of the Horn of Africa between February and July 2011 was 2 - 8 inches (50 - 200 mm) below average, leading to a deadly drought in the region. Image credit: NOAA Climate Prediction Center.

Another day of dangerous heat in the Midwest
The dangerous Central U.S. heat wave of July 2011 will continue to bring another day of exceptionally humid heat to the Midwest today, and will also begin bringing temperatures in the mid-90s with high humidity to much of the mid-Atlantic and New England. The heat index--how hot the air feels when factoring in both the temperature and the humidity--exceeded 100°F in sixteen states in the center of the country on Tuesday, with the dangerous heat extending from Texas northwards to North Dakota, Minnesota, and Wisconsin. At least thirteen deaths are being blamed on the heat in the Midwest. The heat index hit a torrid 129°F at Newton, Iowa on Tuesday, and a heat index in excess of 120° was recorded at several locations in North Dakota, Iowa, Illinois, and Minnesota.


Figure 2. Predicted maximum heat index for Friday, July 22, 2011. Portions of 35 states are predicted to have a heat index in excess of 100°, with a heat index in excess of 115° expected over large portions of Virginia, Maryland, and Delaware. Image credit: NOAA.

Heat wave headed to the Eastern U.S.
The extreme heat will shift slowly eastwards this week, peaking in Chicago today, Detroit and Pittsburgh on Thursday, and New York City and the mid-Atlantic states on Friday. The forecast high of 103° in Washington D.C. for Friday is just 3° below the hottest temperature ever recorded in the city, 106°. This will no doubt stimulate some predictable quotes on global warming. The heat will remain in place over the mid-Atlantic states through Sunday, then ease on Monday when a cold front is expected to pass through. Wunderground's climate change blogger Dr. Ricky Rood has some good insights on the current heat wave in his latest post.

Tropical Storm Bret no threat
Tropical Storm Bret continues to spin off the U.S. East Coast, but is a weak storm with 50 mph winds, and is not expected to affect any land areas. Wind shear is a high 20 - 25 knots, and is expected to remain in the high range for the next three days. The combination of high wind shear and dry air nearby should act to keep Bret from strengthening, and the storm should slowly decay as it heads out to sea over the next few days.

Invest 99L no threat
Satellite imagery suggests that a low pressure system near 34N, 55W, about 500 miles east of Bermuda, is close to tropical depression strength. This system, dubbed Invest 99L, has been given a 60% chance of developing into a tropical depression by NHC. The storm is headed east-northeastwards out to sea, and is not a threat to any land areas. The storm will move over cool ocean waters below 25°C by Thursday morning, so it has just a short window of time to develop.

An African wave worth watching
An African wave near 45W, midway between the coast of Africa and the Lesser Antilles Islands, is currently generating a limited amount of heavy thunderstorms due to the presence of a large amount of dust and dry air from the Sahara. However, this wave has a modest degree of spin to it, and it is possible it could develop once it finds a moister environment near the Bahama Islands early next week. The last few runs of the UKMET model have shown development of this wave by Tuesday over the Bahamas. The ECMWF and NOGAPS models show that this wave will become a strong tropical disturbance by Tuesday over the Bahamas, while the GFS model shows no development. If this wave does develop, it may recurve before hitting the U.S., since the models agree that there will be a large trough of low pressure present over the U.S. East Coast early next week.

Jeff Masters

Drought

Midwest heat wave generates a heat index of 131° in Iowa; Bret no threat

By: JeffMasters, 1:18 PM GMT on July 19, 2011

A unusually intense, long-lasting, and widespread heat wave with high humidities continues to plague the Central U.S. The heat index--how hot the air feels when factoring in both the temperature and the humidity--exceeded 100°F in twelve states on Monday and thirteen on Sunday, with the dangerous heat extending from Texas northwards to North Dakota, Minnesota, and Wisconsin. At least thirteen deaths are being blamed on the heat in the Midwest. The heat index hit a remarkable 131°F at Knoxville, Iowa on Monday, and a heat index in excess of 120° was recorded at numerous locations in Iowa, Minnesota, and Illinois.


Figure 1. Predicted maximum heat index for Thursday, July 21, 2011. Portions of 33 states are predicted to have a heat index in excess of 100°F. Image credit: NOAA.

A 1-in-7-year heat wave coming for the Eastern U.S.
The extreme heat will shift slowly eastwards this week, peaking in Chicago on Wednesday, Detroit and Pittsburgh on Thursday, and New York City and the mid-Atlantic states on Friday. Temperatures near 100°F are expected in Detroit on Thursday and New York City on Friday. Detroit has hit 100°F 18 different years in its 137-year record, and New York City 22 years out of the past 140 years, so this heat wave is expected to be about a 1 in 7 year event. While that makes it a notable heat wave, the most remarkable feature of this July 2011 U.S. heat wave is the humidity that has accompanied the heat. A heat index over 130°F, such as was observed yesterday in Iowa, is very rare in the U.S., and extremely dangerous. According to Christopher C. Burt, wunderground's weather historian, the only place in the world where a heat index over 130°F is common is along the shores of the Red Sea in the Middle East. A major reason for the remarkably high humidities accompanying the July 2011 Midwest heat wave is the record flooding the region experienced over the past three months. As pointed out by wunderground's climate change blogger Dr. Ricky Rood in his latest post, with hundreds of thousands of acres of farmland still inundated by flood waters, and soils saturated over much of the Upper Midwest, there has been plenty of water available to evaporate into the air and cause remarkably high humdities. This makes for a very dangerous situation, as the human body is not able to cool itself as efficiently when the humidity is high. The extreme heat will last through Sunday in the mid-Atlantic, but should end on Monday, when a cold front is expected to sweep across the region. However, the latest models suggest the heat will re-amplify over the Midwest next week.


Figure 2. Tropical Storm Bret at peak intensity, at 5:15 pm EDT on Monday, July 18, 2011. At the time, Bret was building an eyewall and had begun to clear out an eye. Image credit: NASA/GSFC.

Tropical Storm Bret weakens
Tropical Storm Bret enjoyed a brief burst of intensification yesterday afternoon that brought the storm's winds up to 65 mph. However, Bret has sucked in a lot of dry air today, and is now a much weaker storm with winds of just 50 mph. Satellite imagery shows that Bret has not improved in organization this morning, thanks to dry air to the northwest that has been blown into the storm's core by upper-level northwesterly winds. Wind shear is a high 20 - 25 knots, and is expected to remain in the high range for the next three days. The combination of high wind shear and dry air nearby should act to keep Bret from strengthening, and the storm should slowly decay as it heads out to sea over the next few days. Bret is not a threat to any land areas.

None of the reliable models predict tropical cyclone development over the remainder of the Atlantic through July 26.

Weakened Typhoon Ma-on nearing Japan
Typhoon Ma-on has weakened to minimal Category 1 typhoon with 75 mph winds, and is battering a large swath of the south coast of Japan with tropical storm-force winds, as the storm slides northeast along the coast. Ma-on is expected to turn eastwards out to sea by Wednesday, and is not likely to bring tropical storm-force winds to the troubled Fukushima Nuclear Plant.

Jeff Masters

Tropical Storm Bret forms near the northern Bahamas

By: JeffMasters, 2:57 PM GMT on July 18, 2011

Tropical Storm Bret formed last night over the Northwestern Bahama Islands, and is expected to bring heavy rains of 2 - 4 inches to the northernmost Bahama Islands today and Tuesday, as the storm drifts slowly to the north-northeast. Bret's formation date of July 17 is two weeks ahead of the usual formation date for the Atlantic's second storm of the season, which is August 1. The latest data from the Hurricane Hunters, taken between 4 - 5am EDT, showed a 100-mile wide area of tropical storm-force winds in excess of 39 mph affecting only the northernmost Bahama Islands--the Abacos. A personal weather station on Great Abaco Island recorded a wind gust of 48 mph at 12:23 am today. Satellite imagery shows that Bret has not improved in organization this morning, thanks to dry air to the northwest that has been blown into the storm's core by upper-level northwesterly winds. long-range radar out of Melbourne, Florida shows that Bret is currently dumping very little rain over the Bahamas, and one thin rain band from the storm is affecting the Florida East Coast with rainfall amounts less than a quarter inch. Wind shear is a moderate 10 - 15 knots, and sea surface temperatures are 28 - 29°C, which is 2°C above the 26.5°C threshold needed to support a tropical storm.


Figure 1. Morning satellite image of Tropical Storm Bret.

Forecast for Bret
None of the models develop Bret into a hurricane. though the GFDL model has it coming close. Given the current ragged appearance of the storm, plus the forecast by the SHIPS model that wind shear will rise to the high range, 20 - 25 knots, by Tuesday morning, it is unlikely Bret will become a hurricane. NHC is giving Bret a 22% chance of developing into a hurricane by Tuesday.

Steering currents are weak off the coast of Florida, and Bret can be expected to move slowly near 5 mph through Tuesday, before the storm gets caught in a trough of low pressure and lifted northeastwards out to sea. It currently appears that the only land areas that will be affected by Bret will be the northernmost Bahama Islands, today and Tuesday.

None of the reliable models predict tropical cyclone development over the remainder of the Atlantic through July 25.


Figure 2. Visible satellite image of Typhoon Ma-on from NASA's Aqua satellite taken July 18, 2011. Image credit: NASA.

Weakened Typhoon Ma-on headed towards Japan
Typhoon Ma-on has weakened to a large Category 1 storm as it heads towards Japan, and is expected to brush the east coast of the main island of Honshu on Tuesday. The typhoon weakened over the past day, thanks to an eyewall replacement cycle where the inner eyewall collapsed, and a new, larger eyewall formed from an outer spiral band. Ma-on was expected to intensify once this process completed, but the eyewall replacement process significantly disrupted the storm, and it is unlikely Ma-on will be able to recover. This is good news for Japan, since Ma-on is a huge storm with tropical-storm force winds that extend 225 miles north of the center.

Jeff Masters

Hurricane

Tropical Depression Two forms from Invest 98L

By: JeffMasters, 9:33 PM GMT on July 17, 2011

Tropical Depression Two (TD2) formed from Invest 98L this afternoon. Hurricane Hunters flew into the suspect area and found a surface circulation north of the Bahamas, with maximum sustained winds of 35 mph. They also determined the system had become warm core—a characteristic that must be present in order to declare a tropical cyclone. Satellite imagery continues to show the system is becoming more organized with a stronger circulation. Wind shear is forecast to remain favorable for the system until Tuesday or Wednesday when higher shear will slide in from the north. Sea surface temperatures are warm enough to sustain a tropical storm.


Figure 1. Satellite imagery of Tropical Depression Two in the Atlantic, east of Florida. This graphic will update to the current satellite imagery.


Figure 2. Official 5-day forecast for Tropical Depression Two. This graphic will remain current.

Forecast for TD2

The models are coming into better agreement as TD2 has become more organized. In terms of dynamical forecast models, the HWRF and GFS both forecast TD2 to max out just above tropical storm strenth. HWRF intensifies TD2 to around 47 mph in the next 24 hours, whereas GFS is a bit slower to bring the system up to tropical storm status. Two statistical models, the DSHP (SHIPS model that includes land interaction) and the LGEM (Logistical Growth Equation Model) both intensify TD2 to a moderate tropical storm over the next 2-3 days.

There tends to be a lot of uncertainty involved with tropical cyclones that form under these circumstances, but our forecast remains in line with the National Hurricane Center and the reliable forecast models. TD2 will move slowly to the northeast in weak steering currents over the next few days before eventually becoming an extratropical storm. There is minimal chance that this system will cross over Florida into the Gulf of Mexico. Timing and path depend heavily on how intense the cyclone gets, as Jeff mentioned in his blog earlier today. A weaker storm will tend to stay south, whereas a stronger storm will grow taller in the atmosphere and winds at higher levels will influence it and steer it northeast.

None of the reliable models predict tropical cyclone development over the remainder of the Atlantic through July 23.

Angela

Hurricane

98L may develop into a tropical depression near Florida; Ma-on a threat to Japan

By: JeffMasters, 3:09 PM GMT on July 17, 2011

A tropical disturbance (Invest 98L) has formed off the east coast of Florida, along the tail end of a cold front that pushed off the coast late last week. This disturbance has the potential to develop into a tropical depression that will bring heavy rains to the northern Bahamas and east coast of Florida today through Tuesday. Satellite imagery shows that the disturbance has become more organized this morning, with an expanding area of intense thunderstorms, the beginnings of a surface circulation, and upper-level outflow on the east and north sides of the storm. Some rotation of 98L is also evident on long-range radar out of Melbourne, Florida, but the rain showers are poorly organized and there is little evidence of low-level spiral banding. Wind shear is a moderate 10 - 20 knots, and sea surface temperatures are 27 - 28°C, which is plenty warm enough to support a tropical storm. There is dry, continental air over North Florida, and upper level winds out of the northwest are driving this dry air into the center of 98L, retarding development.


Figure 1. Morning satellite image of Invest 98L.

Forecast for 98L
The models are shy about developing 98L; only the HWRF model shows a tropical depression developing. The SHIPS model predicts that wind shear will be in the low to moderate range, 5 - 15 knots, over the next five days. NHC is giving 98L a 30% chance of developing into a tropical depression by Wednesday. Given the recent satellite and radar presentation of the storm, I'd put those odds higher, at 50%. A hurricane hunter aircraft is scheduled to investigate 98L this afternoon.

Steering currents are weak off the coast of Florida, and 98L can be expected to move slowly at less than 5 mph over the next two days. The HWRF and GFDL models predict 98L will execute a clockwise loop, heading towards the coast of Florida on Monday, then looping northeastwards towards South Carolina later in the week. The track of 98L will depend strongly on how intense the storm gets; a weak system is likely to stay farther to the south, while a stronger system will "feel" upper level winds with a west-to-east component, and tend to move to the northeast, parallel to the coast.

None of the reliable models predict tropical cyclone development over the remainder of the Atlantic through July 23.

U.S. heat wave to last at least another week
An unusually intense, widespread, and long-lasting heat wave over the majority of the U.S. continues to set numerous daily record highs. The latest long-range forecasts from the GFS and ECMWF models predict that the ridge of high pressure responsible for the heat wave will remain entrenched over the center or eastern portion of the country during the coming week, so the heat wave should continue for all but the Pacific Northwest through July 23. The GFS model does show that the ridge will break down some during the period 10 - 16 days from now, but such long range forecasts have low skill, and the heat wave could easily continue through the remainder of July. I'll present a more detailed look at the heat wave later this week.


Figure 2. Microwave satellite image of Typhoon Ma-on at 08:26 UTC July 17, 2011, over the West Pacific Ocean. The typhoon was undergoing an eyewall replacement cycle, with the inner eyewall collapsing and a new, larger eyewall forming from an outer spiral band. Image credit: Navy Research Lab, Monterey.

Typhoon Ma-on headed towards Japan
Powerful Category 3 Typhoon Ma-on is headed northwestward towards Japan, and is expected to brush the east coast of the main island of Honshu on Tuesday. The typhoon has weakened some over the past day, thanks to an eyewall replacement cycle where the inner eyewall collapsed, and a new, larger eyewall formed from an outer spiral band. Once this process completes, Ma-on is expected to intensify into a Category 4 storm. With water temperatures along the path of the typhoon ranging from 29 - 30°C, and wind shear expected to remain in the low to moderate range of 5 - 15 knots, Ma-on has the potential to hit Japan as a major Category 3 storm. The typhoon is unusually large, with winds of tropical storm force (39+ mph) extending out almost 350 miles to the north of the storm. A large portion of the south coast of Japan will receive tropical storm-force winds and large battering waves from Ma-on. Although the typhoon is currently a minimal Category 3 storm, its large size means that Ma-on has a tremendous amount of total kinetic energy, characteristic of a Category 5 storm. This means that Ma-on has the potential to bring a large and highly destructive storm to the coast on the right front side of where the eye makes landfall. If the eye remains just offshore, as some models are predicting, this storm surge will largely miss Japan, though.

Jeff Masters

Hurricane

Globe has 7th warmest June on record; Typhoon Ma-on a threat to Japan

By: JeffMasters, 5:13 PM GMT on July 15, 2011

June 2011 was the globe's 7th warmest June on record, according to the National Oceanic and Atmospheric Administration (NOAA) National Climatic Data Center (NCDC). NASA's Goddard Institute for Space Studies rated June the 8th warmest on record. June 2011 global land temperatures were the 4th warmest on record, and ocean temperatures were the 10th warmest on record. Global satellite-measured temperatures for the lowest 8 km of the atmosphere were well above average, the 5th or 3rd warmest in the 34-year record, according to Remote Sensing Systems and the University of Alabama Huntsville (UAH). Ocean temperatures in the Atlantic Main Development Region for hurricanes, from the coast of Central America to the coast of Africa between 10°N and 20°N, were 0.9°C above average, the 5th warmest such temperatures in the past 160 years. The record was set in 2010, with a temperature of 1.3°C above average.


Figure 1. Departure of temperature from average in June 2011. Image credit: National Climatic Data Center (NCDC).

Record cold temperatures in the stratosphere
Global temperatures in the lower stratosphere, where the bulk of Earth's protective ozone layer lies, were at their coldest levels on record during June, according to both the University of Alabama and RSS, Inc. This is the second consecutive month of record cold in the stratosphere. Global warming theory predicts that in order to counter-balance the large amount of warming that occurs in the lower atmosphere near the surface when heat-trapping gases such as carbon dioxide are released into the air, the stratosphere must cool. Thus, a record cold stratosphere is consistent with global warming. However, the majority of the stratospheric cooling that has occurred since the 1990s is probably due to destruction of ozone by chlorine-containing gases like CFCs. Ozone strongly absorbs solar energy, warming the air around it, so if there is less ozone around, there will be less absorption of solar energy and a thus a cooler stratosphere.

Earlier this year, the World Meteorological Organization announced that depletion of the ozone layer—the shield that protects life on Earth from harmful levels of ultraviolet rays—reached an unprecedented level over the Arctic this spring because of the continuing presence of ozone-depleting substances in the atmosphere, and a very cold winter in the stratosphere. The Arctic ozone declined 40% between December and March.

U.S. heat wave to last at least another week
An unusually intense, widespread, and long-lasting heat wave over the majority of the U.S. continues to set numerous daily record highs. The latest long-range forecasts from the GFS and ECMWF models predict that the ridge of high pressure entrenched over the country responsible for the heat wave will move little over the coming week, and the heat wave should continue for all but the Pacific Northwest through July 23. The GFS model does show that the ridge will break down some during the period 10 - 16 days from now, but such long range forecasts have low skill, and the heat wave could easily remain entrenched over the country through the rest of July. I'll present a more detailed look at the heat wave next week.


Figure 2. Typhoon Ma-on at 04:15 UTC July 15, 2011, over the West Pacific Ocean. The small swirl at lower left is Tropical Depression Tokage. Image credit: NASA.

Typhoon Ma-on headed towards Japan
Powerful Category 4 Typhoon Ma-on is headed westward over the West Pacific Ocean, but is expected to encounter a trough of low pressure this weekend that will recurve the storm to the north and northeast, bringing it very close to the coast of Japan early next week. With water temperatures along the path of the typhoon ranging from 28 - 30°C, and wind shear expected to remain in the moderate range, 10 - 20 knots, Ma-on has the potential to hit Japan as a major Category 3 storm.

The Atlantic is quiet
None of the reliable models predict tropical cyclone development through July 21.

I'll have a new post by Monday at the latest.

Jeff Masters and Angela Fritz

Climate Summaries

2011 the most expensive year for natural disasters in history

By: JeffMasters, 2:42 PM GMT on July 14, 2011

An exceptional accumulation of very severe natural catastrophes, including earthquakes in Japan and New Zealand, tornadoes and flooding in the U.S., and flooding in Australia and New Zealand, make 2011 the highest-ever loss year on record, even after the first half-year, said re-insurance giant Munich Re in a press release this week. The $265 billion in economic losses accumulated this year exceeds the previous record year, 2005, which had $220 billion in damage (mostly due to $125 billion in damage from Hurricane Katrina.) Unlike 2005, this year's losses have been headlined by two huge earthquakes--the March 11 quake in Japan ($210 billion) and the February 22 quake in New Zealand ($20 billion.) But with the Northern Hemisphere's hurricane season just beginning, this year's record losses may see a significant boost from hurricanes.


Figure 1. Stunned survivors survey the destruction left by the EF-4 Tuscaloosa-Birmingham tornado of April. With a price tag estimated at $2 billion, this was the single most expensive tornado of all-time. The record stood only three weeks, being surpassed by the $3 billion in damage from the Joplin Missouri, tornado. The two tornado outbreaks that spawned these tornadoes rank as the globe's 3rd and 5th most destructive natural disasters so far this year. Image from an anonmous posting to Twitter.

Climate change and damage from weather-related disasters
In an interview with MSNBC, Peter Hoppe, who runs Munich Re's Geo Risks Research/Corporate Climate Center, said that while the damage trend for earthquakes, tsunamis and volcanic eruptions is fairly stable, damage from severe weather events is on the upswing, even after factoring in increases in population and wealth. He cited natural events such as La Niña and El Niño as factors in some of the damaging weather events, but added that warming temperatures appear to be adding a layer "on top" of that natural variability. In particular, he noted that the floods this January in Australia--that nation's most expensive natural disaster of all time--occurred when ocean temperatures off the coast were at record warm levels. That meant "more evaporation and higher potential for these extreme downpours", and "it can only be explained by global warming."


Figure 2. The five most expensive natural disasters of 2011, as estimated by Munich Re.

However, the there is a lot of controversy on whether economic losses due to weather-related disasters is increasing due to climate change. A 2010 paper in the Bulletin of the American Meteorological Society by Netherlands researcher Laurens Bouwer titled, "Have disaster losses increased due to anthropogenic climate change?", looked at 22 disaster loss studies in various parts of the world. All of the studies showed an increase in damages from weather-related disasters in recent decades. The big question is, how much of this increase in damage was due to increases in population, and the fact people are getting wealthier, and thus have more stuff to get damaged? Fourteen of the 22 studies concluded that there were no trends in damage after correcting for increases in wealth and population, while eight of the studies did find upward trends even after such corrections. In all 22 studies, increases in wealth and population were the "most important drivers for growing disaster losses."

Bouwer's review of these 22 disaster loss studies was critiqued this year by Neville Nicholls of the School of Geography and Environmental Science of Montash University, Australia. His analysis, published in the Bulletin of the American Meteorological Society, notes that Bouwer's study of damage losses did not include the impact of improvements in building codes and weather forecasting. We can expect both factors to have significantly reduced damages due to storms in recent years. Nicholls concludes, "The absence of an upward trend in normalized losses may be due to a balance between reduced vulnerability (from improved weather forecasting and building techniques) and increased frequency or intensity of weather hazards." In his reply to Nicholls' comments, Bouwer states that Nicholls "provides no support that these factors have actually contributed to a substantial reduction in losses over the period of the last decades."

Jeff Masters

Climate Change

Invest 97L bringing heavy rains to Mexico

By: JeffMasters, 2:03 PM GMT on July 13, 2011

A tropical disturbance (Invest 97L) in the southernmost Gulf of Mexico in the Bay of Campeche has spun up very quickly into an impressive system with very heavy thunderstorm activity. Radar out of Alvarado, Mexico is showing some rotation to 97L, and the system is close to tropical depression strength. In a special statement issued at 9:15am EDT, NHC gave 97L a 50% chance of development before the storm moves ashore over Mexico this afternoon. The topography of the Bay of Campeche features mountains that help accelerate the counter-clockwise flow of low-level winds, making the region prone to sudden spin-ups of tropical storms.


Figure 1. Morning satellite image of Invest 97L.

97L a heavy rainfall threat
It is already raining in Veracruz, just to the south of where the center of 97L is expected to make landfall. Heavy rains of 3 - 6 inches can be expected over Mexico today and Thursday along 97L's track. These rains may cause flooding problems, particularly since the region impacted has been under extreme drought this year. The drought has killed much of the vegetation that ordinarily would slow down run-off. In late June, Tropical Storm Arlene brought flooding rains in excess of ten inches (250mm) to the coast just north of where 97L is expected to make landfall. These floods killed 22 people.



Figure 2. On June 30, 2011, Tropical Storm Arlene made landfall near Cabo Rojo in Veracruz, Mexico. The impact of Arlene’s heavy rain was clear in early July as the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite passed overhead. MODIS captured the top image on July 5, 2011. For comparison, the bottom image shows the same area on June 19, 2011. The images use a combination of visible and infrared light to increase contrast between water and land. Water varies from electric blue to navy. Depending on land cover, areas above water range in color from green to brown. Clouds are pale to medium blue-green. A network of lakes extends inland from the city of Tampico. In the image from July 5, the lake network appears to have multiplied, with standing water covering large areas northwest and southwest of the city. Standing water is also apparent south of Cabo Rojo. Image credit: NASA.

The latest runs of the reliable models do not predict any tropical cyclone development over the next seven days,

I'll have a new post late this afternoon or early Thursday morning.

Jeff Masters

June 2011: another month of exceptional extremes for the U.S.

By: JeffMasters, 2:24 PM GMT on July 11, 2011

June 2011 was another month of remarkable extremes over the U.S. Overall, it was the 26th warmest and 19th driest June for the lower 48 states, according to the National Climatic Data Center. Extreme heat gripped much of the South, with Texas experiencing its hottest June on record, and 13 other states recording top-ten hottest Junes. Accompanying the heat was intense drought--New Mexico had its driest June on record, and four other states had top-ten driest Junes. While the southern Plains' 1950s drought of record is unsurpassed in terms of duration, the current drought in parts of Texas is more intense than the 1950s drought when measured by the Palmer Hydrological Drought Index. The heat and drought contributed to the worst fire year in U.S. history, with 4.8 million acres burned by the end of the month, more than double the average from the previous ten years.

While the South baked and burned, California experienced its wettest June on record, and heavier than normal precipitation and prolonged snowmelt during the spring caused June flooding in Idaho, Montana, North Dakota, Utah, and Washington. For the 3-month period April-May-June, the NOAA Climate Extremes Index indicated that it was the most extreme such period on record in the U.S. for precipitation, as measured by the percent area of the U.S. experiencing top 10% wettest or driest conditions. Heavy 1-day precipitation events were also at an all-time high during April-May-June 2011. Data for the Climate Extremes Index goes back to 1910.


Figure 1. Exceptional heat gripped most of the South during June 2011, with Texas experiencing its hottest June in 117 years of record keeping, and 13 other states recording a top-ten hottest June. Image credit: NOAA/NCDC.


Figure 2. Exceptionally dry conditions accompanied the intense heat in the South during June 2011, with New Mexico experiencing its driest June in 117 years of record keeping, and four other states recording a top-ten driest June. Image credit: NOAA/NCDC.

Tornado activity died down in June
According to data from the Storm Prediction Center, there were 177 preliminary tornado reports during June, which is below the national average for the month. On June 1st, a strong tornado tracked 39 miles across Massachusetts, marking the second longest tornado track on record for the state.

The Atlantic is quiet
A tropical wave near 10°N, 55°W, about 500 miles east of the southern Lesser Antilles Islands, is moving west at 15 - 20 mph, and will bring heavy rain to the southern Lesser Antilles and the northeast coast of South America on Tuesday and Wednesday. Wind shear over the wave is low, 5 - 10 knots, but the wave is too close to the Equator to leverage Earth's spin in time for development. NHC is giving the wave a 10% chance of developing into a tropical depression by Wednesday.

The NOGAPS models is predicting that a strong tropical disturbance could develop in the Gulf of Mexico's Bay of Campeche by Sunday, similar to how Tropical Storm Arlene developed at the end of June. The latest runs of the other reliable models do not predict any tropical cyclone development of note over the next seven days, though the GFS model was showing development of a system off the coast of Africa this week, in its run from Sunday night.

Jeff Masters

Climate Change

Arctic sea ice in record retreat

By: JeffMasters, 3:42 PM GMT on July 08, 2011

The summer melt season is in full swing in the Arctic, and sea ice there is in record retreat. Arctic sea ice is currently at its lowest extent on record for early July, according to estimates from the National Snow and Ice Data Center and University of Bremen. Moreover, Arctic sea ice volume is at its lowest on record, according to the University of Washington Polar Science Center, and during June 2011, was reduced by nearly half (47%) compared to its maximum at the beginning of the satellite era, in 1979. The latest surface analysis from Environment Canada shows a 1039 mb high pressure system centered north of Alaska, which is bringing clear skies and plenty of ice-melting sunshine to the Arctic. The combined action of the clockwise flow of air around the high and counter-clockwise flow of air around a low pressure system near the western coast of Siberia is driving warm, southerly winds into the Arctic that is pushing ice away from the coast of Siberia, encouraging further melting. This pressure pattern, known as the Arctic Dipole, was dominant over the Arctic during June, leading to June having the 2nd lowest extent on record, and the record low extent observed at the beginning of July. The Arctic Dipole began emerging in the late 1990s, and was unknown before then; thus climate change is suspected as its primary cause. The Arctic Dipole has become increasingly common in the last six years, and has contributed significantly to the record retreat of Arctic sea ice.


Figure 1. Arctic sea ice extent as of July 7, 2011, as estimated by the National Snow and Ice Data Center. Ice extent during the first week of July was slightly less than the previous record low set in 2007 (dashed green line.)

The previous all-time record year for sea ice loss: 2007
The all-time summer Arctic sea ice melt occurred in 2007, when a "perfect storm" of weather conditions came together to cause a stunning amount of ice loss. Unusually strong high pressure over the Arctic led to clear skies and plenty of sunshine. Arctic winds, which usually blow in a circular fashion around the Pole, instead blew from the south over Central Siberia, due to the Arctic Dipole pattern, injecting large amounts of warm air into the Arctic. Sea ice loss, which had been 20% in the summer of 2006 compared to the summer of 1979, doubled to 39% in 2007, according to the National Snow and Ice Data Center. In one year, as much ice was lost as in the previous 28 years. Compared to the 1950s, over half of the Arctic sea ice had disappeared.


Figure 2. Arctic sea ice extent since 1900, as estimated from satellite and ship reports compiled by Walsh and Chapman (2001). Image credit: University of Illinois cryosphere group.

The forecast
Summertime Arctic sea ice loss since 2007 has not been as severe, due to cooler and cloudier conditions. However, ice loss in 2008 - 2010 was worse than any year prior to 2007, and the amount of old, thick, multi-year ice has suffered steep declines. How often, then, might we expect to see a "perfect storm" of weather conditions capable of triggering record sea ice loss like in 2007? Well, at the December 2008 meeting of the American Geophysical Union, the world's largest scientific conference on climate change, J.E. Kay of the National Center for Atmospheric Research showed that Arctic surface pressure in the summer of 2007 was the fourth highest since 1948. Cloud cover at Barrow, Alaska was the sixth lowest. This suggests that once every 10 - 20 years a "perfect storm" of weather conditions highly favorable for ice loss invades the Arctic. The last two times such conditions existed was 1977 and 1987.

The latest 1-week forecast from the Canadian GEM model shows the Arctic Dipole pattern continuing, but with high pressure gradually weakening over the Arctic. This should decrease the southerly winds blowing warm air into the Arctic, and help slow down the current record retreat to just below record levels. However, the latest 2-week forecast from the GFS model shows high pressure will build back in over the Arctic during the last half of July, which would tend to increase the flow of warm air into the region again. Overall, it appears that the weather conditions during July 2011 will end up not being as favorable for ice loss as July 2007 was, but the ice is more vulnerable to melting than in 2007 due to the significant loss of old, thick, multi-year ice since 2007. It is too early to tell what may occur during August, but the forecast for July leads me to believe that we will come very close to breaking the 2007 record for all-time ice loss in September, but fall just short. Of the seventeen outlooks issued in early June by various scientific groups, only four called for 2011 to exceed 2007 for summer Arctic sea ice loss.


Figure 3. Distribution of individual Pan-Arctic Outlook values (June Report) for September 2011 sea ice extent. Image credit: ARCUS.

Invest 96L in the Atlantic little threat
An area of disturbed weather (Invest 96L) in the Gulf of Mexico centered a few hundred miles west of Tampa, Florida has become disorganized due to high wind shear of 15 - 25 knots. The latest SHIPS model forecast predicts the shear will be a moderate 10 - 20 knots over the next two days as 96L moves slowly northwards towards the Florida Panhandle. The shear should keep any development slow. Water vapor satellite images show that 96L is located on the east side of an upper-level low pressure system centered over southern Louisiana. This upper level low is pumping dry, stable air into the west side of 96L, which will retard development. There is no sign of a surface circulation in 96L, and none of the reliable computer models is developing it. NHC is giving 96L a 10% chance of developing into a tropical depression by Sunday. The storm has brought a region of 2 - 4 inches of rain to the coast near Tampa, and portions of the Florida Panhandle coast will likely receive 2 - 4 inches of rain this weekend when 96L moves in.


Figure 4. Radar estimated rainfall from 96L as of Friday morning.

My Arctic sea ice page has more info on Arctic sea ice, including why we care about it, and predictions on when it might all disappear.

My next post will be Monday, unless there's some unexpected development to report.

Jeff Masters

Summer Midwest flooding could rival 1993 as most expensive in history

By: JeffMasters, 1:52 PM GMT on July 07, 2011

Heavy rains this summer could trigger floods that would rival America's most expensive flood disaster of all-time, said NOAA in a press release yesterday. The most expensive flood in America occurred in 1993, when torrential summer rains caused a $25 billion flood along the Missouri River and surrounding regions of the Upper Midwest. Record 100-year flooding has already occurred along many stretches of the Missouri, Souris, James, North Platte, and other rivers in the Upper Midwest over the past month. With rivers running high and soils completely saturated this summer, just a small amount of rain could trigger more flooding, including areas that have already seen major to record flooding. "The sponge is fully saturated--there is nowhere for any additional water to go," said Jack Hayes, Ph.D., director of NOAA's National Weather Service. "While unusual for this time of year, all signs point to the flood threat continuing through summer."

Throughout the rest of the summer, the highest flood risk areas include:

- North Central U.S. including Souris River (North Dakota) and Red River of the North (border of North Dakota and Minnesota), Minnesota River (Minnesota), Upper Mississippi River (Minnesota and Iowa), and Des Moines River (Iowa)
- Lower Missouri River from Gavin’s Point (Nebraska and South Dakota border) downstream along the border of Nebraska and Iowa, continuing through the borders of Kansas and Missouri then through Missouri to the Mississippi River
- Tributaries to the Lower Missouri including the James and Big Sioux Rivers in North Dakota
- Lower Ohio River Valley including the White, Wabash and lower Ohio River
- East of Rockies: North Platte River in Colorado, Wyoming and Nebraska and Yellowstone River in Wyoming and Montana
- West of Rockies: Utah and Colorado

The latest 3-month precipitation forecast from NOAA's Climate Prediction Center (Figure 1) show an above average chance of heavy rains over much of the Upper Midwest this summer.


Figure 1. Precipitation forecast for July-August-September as issued by NOAA's Climate Prediction Center. Above average chances of heavy precipitation (green colors) are expected over much of the Upper Midwest.

June 2011 was highest single month of runoff in Missouri River Basin since 1898
The Army Corps of Engineers announced this week that runoff into the Missouri River Basin above Souix City, Iowa during June was the highest single runoff month since records began in 1898. June 2011 runoff into the Missouri River Basin above Sioux City was 13.8 million acre feet (maf.) The previous record was 13.2 maf in April of 1952; May of this year now holds the record for 3rd greatest runoff, 10.5 maf. The May and June combined runoff totaled 24.3 maf, just short of the normal total annual runoff for the entire basin which is 24.8 maf. Four federal levees and 11 non-federal levees have breached or overtopped across Iowa, Kansas, Nebraska and Missouri so far this year along the Missouri River.


Figure 2. Flood heights were rising rapidly on the Yellowstone River the night of the pipeline disaster on July 1, 2011. A few hours after the disaster, the river crested just below moderate flood stage of 14' in Billings, about twenty miles downstream from where the pipeline broke in Laurel, Montana. This was the 3rd highest flood on record at this location, with records extending back to 1904. Image credit: NWS.

Oil spill in Yellowstone River likely influenced by flooding
An Exxon Mobil oil pipeline under the Yellowstone River burst on Friday night, spilling at least 42,000 gallons of oil into the river. The prevailing theory among officials and the company is that the raging Yellowstone eroded the riverbed and exposed the line to damaging rocks or debris. The river was rising rapidly the night of the break, and crested at 13.95', the third highest flood in recorded history. Records extend back to 1904 at the site. Crude has been reported as far as 240 miles downstream, although most appears to be concentrated in the first 25 miles. The Yellowstone is a tributary of the Missouri River.


Figure 3. Morning satellite image of 96L and the tropical wave approaching South America.

Invest 96L in the Atlantic little threat
An area of disturbed weather in the Gulf of Mexico centered just west of the Florida Keys has been labeled Invest 96L by NHC this morning. The disturbance is under high wind shear, about 20 - 25 knots, and the latest SHIPS model forecast predicts the shear will be 15 - 25 knots over the next two days as 96L moves slowly northwards towards the Florida Panhandle. The high shear should keep any development slow. Water vapor satellite images show that 96L is located on the east side of an upper-level low pressure system centered a few hundred miles south of New Orleans. This upper level low is pumping dry, stable air into the west side of 96L, which will retard development. There is no sign of a surface circulation in 96L, and none of the reliable computer models is developing it. NHC is giving 96L a 10% chance of developing into a tropical depression by Saturday.

The other area of note is a tropical wave about 600 miles east of the southernmost Lesser Antilles Islands. This wave is under 10 - 20 knots of wind shear, and may show some modest development before moving ashore over the northern coast of South America on Saturday. NHC is giving this disturbance a 10% chance of developing into a tropical depression by Saturday. The disturbance is too close to the Equator to leverage Earth's spin much, which will slow any possible development.

Jeff Masters

Massive haboob duststorm sweeps through Phoenix

By: JeffMasters, 3:15 PM GMT on July 06, 2011

A massive desert sandstorm roared through Phoenix, Arizona last night, dropping visibilities to near zero and coating surfaces with a gritty later of dust and sand. The phenomenon, known as a haboob, occurs when the outflow from a thunderstorm kicks up desert dust. Last night's haboob was due to a large complex of thunderstorms known as a mesoscale convective system (MCS) that developed to the east of Phoenix. As the outflow from the MCS hit the ground, large quantities of sand and dust became suspended in the air by 50 - 60 mph winds. The amount of dust was much greater than is usual for one of these storms, due to the large size of the thunderstorm complex, and the extreme drought conditions the region has been experiencing. As the haboob hit Phoenix, winds gusted to 53 mph at Sky Harbor International Airport, and the airport was forced to shut down for 45 minutes due to visibilities that fell as low as 1/8 mile. The airport received only 0.04" of rain from the storm, but large regions of Southern Arizona got 1 - 2 inches of rain overnight due to the monsoon thunderstorms. The Southwest U.S.'s annual monsoon season has kicked into gear this week, aided by moisture from Tropical Storm Arlene. The welcome rains the monsoon's thunderstorms will bring to the region should greatly aid the efforts of firefighters attempting to control the fires of the Southwest's worst fire season in recorded history. The latest 5-day precipitation forecast from NOAA's Hydrometeorological Prediction Center is calling for widespread areas of 1/2 - 1 inch of rain over Arizona and western New Mexico this week.


Figure 1. Radar-estimated rainfall from last night's monsoon season thunderstorms that swept through Southern Arizona.


Video 1. Helicopter video of the impressive haboob sandstorm from July 5, 2011, as it swept through downtown Phoenix. Here is a time lapse video of what it was like to drive into the sandstorm.

The Atlantic is quiet
The Atlantic is quiet, with no threat areas to discuss. None of the reliable computer model is predicting tropical cyclone formation over the next seven days.

Jeff Masters

2011 now tied for 1st for the most EF-5 tornadoes in one year: 6

By: JeffMasters, 1:58 PM GMT on July 05, 2011

The National Weather Service completed damage surveys last month in Alabama on the massive April 25 - 27 tornado outbreak, and found evidence to upgrade another tornado from the outbreak to EF-5 status with winds in excess of 200 mph: the Rainsville, Alabama tornado of April 27, 2011. Damage included houses that were completely removed from foundations and debris scattered for about one mile, trees that were debarked, and a few mobile homes completely destroyed with debris strewn for about a mile downwind. EF-5 damage included a pickup truck that was thrown and torn into multiple pieces, and an 800 pound steel safe anchored to a foundation that was torn away, thrown 600 feet, and had its door ripped from its hinges. Twenty-six people died in the tornado.


Figure 1. The remains of a school bus that was blown across Highway 75 in Rainsville, Alabama during the EF-5 tornado of April 27, 2011. This bus was originally sitting in the parking lot adjacent to the building in the distance to the right. Image credit: National Weather Service.


Figure 2. Number of strong to violent EF-3, EF-4 and EF-5 tornadoes from 1950 to 2011. The year 2011 now ranks in 2nd place behind 1974, with 77 of these tornadoes. There is not a decades-long increasing trend in the numbers of these most dangerous of tornadoes, making any link to climate change for this year's terrible tornado season difficult to support. Image credit: NOAA/National Climatic Data Center (updated using stats for 2008 - 2011 from Wikipedia.)

Six EF-5 tornadoes have now been confirmed by the National Weather Service in 2011. This ties the year 1974 for most top-end tornadoes in one year. Here are the 2011 EF-5 tornadoes:

1) The April 27, 2011 Neshoba/Kemper/Winston/Noxubee Counties, Mississippi tornado (3 killed, 29 mile path length.)

2) The April 27, 2011 Smithville, Mississippi tornado (22 killed, 15 mile path length.)

3) The April 27, 2011 Hackleburg, Alabama tornado (71 killed, 25 mile path length.)

4) The April 27, 2011 Rainsville, Alabama tornado (26 killed, 34 mile path length.)

5) The May 22, 2011 Joplin Missouri tornado (157 killed, 14 mile path length.)

6) The May 24, 2011 Binger-El Reno-Peidmont-Guthrie, Oklahoma tornado. (9 killed, 75 mile path length.)


Video 1. The EF-5 tornado that hit Rainsville, Alabama on April 27, 2011 was caught on video as it was re-forming. Tornado formation videos are rare, and this video shows how dangerous it can be to wait until you see a tornado to take shelter. A powerful tornado can form right on top of you with only a few seconds warning.

The Atlantic is quiet
The Atlantic is quiet, with no threat areas to discuss. The only model showing potential activity over the next seven days is the NOGAPS, with predicts that a low pressure system with tropical characteristics may form on Saturday off the coast of North Carolina, in association with a cold front pushing off the coast. If such a storm does form, it would move northeastwards out to sea, and likely not be a threat to land.

I'll be back with a new post Wednesday or Thursday.

Jeff Masters

Heavy rains from Arlene kill 17 in Mexico

By: JeffMasters, 2:36 PM GMT on July 03, 2011

Heavy rains from Tropical Storm Arlene created flash floods and mudslides that killed eleven people in Mexico over the past three days, according to media reports. Rainfall amounts as high as ten inches were estimated by satellite over the mountainous regions of Mexico where most of the fatalities occurred. The soil in the region was prone to more dangerous flash floods than usual, due to extreme drought conditions that killed much of the soil-stabilizing vegetation.


Figure 1. Satellite-based rainfall estimates from NASA's TRMM satellite for June 24 - July 1, 2011. The solid black line shows the path of Arlene with storms symbols marking the 00 and 12Z positions and intensity. Most of the heaviest rain occurs offshore and along the coast. Over land, rainfall totals exceeded 100 to 150 mm of rain (~4 to 6 inches, shown in green) over most of the central east coast of Mexico. In the vicinity of where Arlene made landfall, there are higher amounts in excess of 250 mm (~10 inches, shown in orange). In addition to the rain from Arlene, a passing tropical wave contributed to the rainfall totals over the Yucatan prior to Arlene's formation. Image credit: NASA.

The heat is on
Sizzling summer temperatures set new daily maximum temperature records over many states in the Southwest and Midwest U.S. yesterday. Most notably, Phoenix Arizona hit 118°F, their hottest day since it was 118 on 21 July 2006. If the long-range GFS model is correct, the Midwest could be in for one of its hottest heat waves in recent years next weekend, when a strong ridge of high pressure is expected to move in.

The Atlantic is quiet
The Atlantic is quiet, and none of the computer models is predicting tropical cyclone formation through July 10.

Enjoy your holiday weekend, everyone, and I'll be back with a new post on Tuesday at the latest.

Jeff Masters

Los Conchas Fire New Mexico's largest fire in recorded history

By: JeffMasters, 3:23 PM GMT on July 01, 2011

The largest fire in New Mexico history is now the dangerous Los Conchas wildfire, which continues to threaten Los Alamos, New Mexico. The fire had consumed 94,000 acres (147 square miles) as of Thursday night, matching the 2003 Dry Lakes Fire in Gila National Forest in Southern New Mexico as the largest fire in state history. The Los Conchas fire was fanned yesterday by winds that reached sustained speeds of up to 25 mph, gusting to 34 mph, along with temperatures in the low 80s and humidities as low as 15%. The fire was 3% contained as of Thursday night. Today, winds will be lighter, 10 - 15 mph, and according to the NOAA Storm Prediction Center, these will not be critical fire conditions. Critical fire conditions are not expected in the Southwest U.S. through July 8, which should allow firefighters to gain control of the Los Conchas fire over the weekend. Conditions in the area are so dry that flames reached 500 feet into the air yesterday, and the fire burned downed trees that were scorched in the huge Cerro Grande fire in 2000.

The 4.7 million acres that have burned in the U.S. so far this year is more than double the 10-year average of 2.3 million acres, according to the Interagency Fire Center. Both Arizona and New Mexico have seen their largest fires in recorded history, and Texas has seen the most acreage burned in recorded history. The Christian Science Monitor today quoted Grant Meyer, a geologist at the University of New Mexico in Albuquerque who studies the interaction of climate and weathering processes, as saying: "these big, severe fires are not unprecedented" in hot, dry intervals the region has experienced during the past 10,000 years. "But recent experience down here suggests that what we're looking at in the last few decades is at least as severe and maybe more so than anything we've seen since the last Ice Age." A build-up of fuels from forestry practices that emphasized fire suppression is partly responsible, he said, "but part of it as well--and the data are very good on this --it's climatic warming", as human industrial activity and land-use changes have pumped increasing amounts of carbon dioxide into the atmosphere. A long-term average decline in annual snow pack, which provides the bulk of the region's water, along with rising average temperatures have lengthened the fire season and dried out the fuel.


Figure 1. Summertime temperatures in New Mexico have increased by about 1°F over the past 100 years. Image credit: National Climatic Data Center.


Figure 2. Change in the average date of onset of the spring snow melt runoff pulse between 1950 - 1999. Reddish-brown circles indicate significant trends towards onsets more than 20 days earlier., Lighter circles indicate less advance of the onset. In a few locations, onset is later (blue circles.) The earlier snow melt in large portions of the West has led to a much longer fire season in recent decades. Image credit: Changes in Streamflow Timing in the Western United States in Recent Decades, USGS, 2005 (as reproduced by the USGCRP.)

Warmest and driest month on record for portions of Texas
June 2011 was the warmest and driest month of all-time in Midland, Texas, since records began in 1931. The average temperature was 88°F, beating the old record of 87.2°F set in August 1964. No rain fell, making it the first June in recorded history in Midland where no rain fell. June 2011 was the warmest on record in San Angelo and Borger, 2nd warmest in Austin and Amarillo, 3rd warmest in Dalhart, 4th warmest in San Antonio, and 10th warmest at Brownsville. Yesterday's 3.39" of rain that fell in Brownsville from Tropical Storm Arlene helped make June 2011 the 4th wettest June on record for the city.

The Atlantic is quiet
The Atlantic is quiet, and none of the computer models is predicting tropical cyclone formation through July 8.

Enjoy your holiday weekend, everyone, and I'll be back with a new post on Tuesday at the latest.

Jeff Masters


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

Category 6™

About

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