Category 6™

A Very-Good-News Story: Microbursts and U.S. Aviation

By: Bob Henson , 4:14 PM GMT on June 30, 2016

If you’re one of the millions of Americans who plan to take at least one flight this summer, take heart: you are remarkably well protected from weather during your flight, especially considering the risks that U.S. passengers faced not that long ago. From the 1970s to the 1990s, more than 800 fliers perished in U.S. commercial airline crashes that were linked to microbursts, small but intense downdrafts generated by thunderstorms. It took years of persistence from scientists to raise awareness of the issue and solve the problem. But solve it they did, by developing warning systems that took advantage of Doppler radar, surface wind sensors, and sophisticated software. Thanks to these systems, the last fatal crash of a U.S. passenger plane attributed to a microburst was on July 2, 1994, when a US Airways flight crashed near the Charlotte-Douglas International Airport, killing 37. As of this weekend, we’ll have put that disaster 22 years behind us.


Figure 1. A microburst emerges from a thunderstorm downdraft. Image credit: NWS/Birmingham, AL.


Figure 2. Depending on the amount of moisture in a thunderstorm and its environment, a microburst may be “dry” (left) or “wet” (right). Both types can be dangerous to aircraft. A video by photographer Brian Snider shows the formation of a dramatic wet microburst near Tucson in August 2015. Image credit: NOAA.

A stealthy villain
Microbursts emerged as a major threat when the mid-century boom in consumer aviation put thousands more flights aloft. It was in the 1970s that the eminent storm researcher T. Theodore Fujita analyzed the risk from localized downdrafts related to convection (the upward motion related to instability that leads to showers and thunderstorms). First trained as a mechanical engineer, Fujita took a research flight in 1945 over the debris left by the bombs that struck Hiroshima and Nagasaki and observed starburst damage patterns emanating outward from the greatest impact points of the bombs. Later, while surveying damage from the Super Outbreak of tornadoes of April 3, 1974, Fujita recognized similar starburst patterns, and he concluded that some of the damage must have resulted from descending wind bursts.

The next year, an Eastern Airlines flight crashed while landing at John F. Kennedy International Airport in New York on June 24, 1975, killing 113. Fujita was enlisted to help analyze the disaster. In a 1976 report, he remarked on “four to five cells of intense downdrafts which are to be called ‘downburst cells’. Apparently, those aircraft which flew through the cells encountered considerable difficulties in landing, while others landed between the cells without even noticing the danger areas on both sides of the approach path.” Fujita estimated that the peak downdraft speed several hundred feet above ground was up to eight times higher than conventional thinking would have predicted. Alas, he added, “there is no way of predicting the occurrence of these phenomena both in time and space.”

Even with very limited data, Fujita’s legendary analytic skills enabled him to see the core process at work: “In general, the air near the ground spreads out violently from the ‘outburst center,’ the spreading center above the ground. Unless a heading correction is made immediately, an aircraft in the crosswind burst will drift away from its expected course. If an aircraft flies straight into the outburst center, its indicated airspeed will increase momentarily followed by a high rate of sink. Before the aircraft can break out of the downburst cell, its indicated air speed will drop suddenly, due to an increase in the tailwind component.”


Figure 3. Diagram showing how a microburst could bring down an aircraft that flies directly through it. Modern warning systems now allow air traffic controllers to steer passenger planes safely around microbursts. Image credit: NCAR Research Applications Laboratory.

From dismissal to acceptance
Fujita’s ideas faced widespread skepticism, as noted by Josh Chamot (National Science Foundation, or NSF): “Until the mid-1970s, most researchers believed that downdrafts would substantially weaken before reaching the ground and not pose a threat to aircraft. They blamed tornadoes and gust fronts as the primary causes of storm damage.” After the JFK crash, the FAA developed a simple cluster of anemometers called LLWAS that could detect wind shear related to large-scale phenomena such as a frontal passage, but the LLWAS sensors were not close enough together to detect microbursts and other crucial small-scale features.

Meanwhile, Fujita and colleagues at the National Center for Atmospheric Research (NCAR) carried out several field campaigns with NSF support, designed to convince scientists and policymakers of the hazard and figure out how to address it. The first of these was Project NIMROD (Northern Illinois Meteorological Research on Downburst). On May 29, 1978, Fujita and NCAR’s James Wilson became the first scientists to detect a microburst on radar. “It was right on top of us,” Wilson told me in a 2010 interview. After this event, Fujita created a new category, microbursts, to denote downbursts less than 4 kilometers (2.5 miles) across.

Project NIMROD detected about 50 microbursts. A follow-up project in 1982, JAWS (Joint Airport Weather Studies) found dozens more near Denver’s now-defunct Stapleton International Airport. When JAWS kicked off its operations that summer, “the FAA was still not ready to admit there was such a thing as a microburst,” according to Wilson. But midway through the project, on July 9, 1982, a Pan Am aircraft was forced down by a microburst in a residential neighborhood in Kenner, Louisiana, killing all 145 people on board and 8 others on the ground. That calamity helped jump-start FAA funding for the remainder of the summer. The agency’s involvement in research accelerated further after a microburst-related 1985 Delta crash near Dallas-Fort Worth International Airport took 137 lives.


Figure 4. NCAR’s John McCarthy spent much of his time during the summers of 1984 and 1985 in the control tower of Denver’s Stapleton International Airport during the CLAWS project (Classify, Locate, Avoid Wind Shear). Image credit: UCAR.


Several more field projects followed, as did NCAR’s development of an enhanced version of the LLWAS system that’s now in place at more than 100 U.S. airports. NCAR and MIT’s Lincoln Laboratory also began collaborating with the FAA to develop a radar-based warning system called Terminal Doppler Weather Radar. TDWR systems were deployed at 45 U.S. airports in the late 1980s and 1990s, parallel with the NWS NEXRAD deployment. Along with the warning system, there was newfound pilot awareness of the wind shear hazard. All of the world’s commercial jet pilots were soon required to take part in a wind shear training program, and a powerful series of videotapes featured pilots sharing their stories of microburst encounters. Together, these innovations led to the essential vanquishing of microburst-related accidents on U.S. passenger planes since the mid-1990s.

Outside the U.S., “most international airports have no wind shear protection,” said Bruce Carmichael, director of NCAR’s Aviation Applications Program. “However, the new generation of aircraft radar systems include forward-looking wind shear warnings, so there is a good deal of capability inherent in the aircraft.”

In the realm of general aviation (all civilian flights outside of scheduled passenger service), wind shear remains a deadly threat, because most of those flights involve smaller aircraft and airports that lack the means of detecting wind shear. Still, there is only an average of about 10 shear-related fatalities per year in U.S. general aviation, compared to the 400-plus general aviation deaths related to weather hazards as a whole.


Figure 5. An intense hailstorm bears down on the NWS NEXRAD radar located at Front Range Airport, just southeast of Denver International Airport, on May 21, 2014. A separate radar at DIA that focuses on smaller-scale phenomena is part of the FAA’s Terminal Doppler Weather Radar network. The storm was part of a multiday outbreak of severe weather from the Rockies to the Northeast U.S. (May 18-23) that caused $4 billion in damage. Image credit: Bob Henson.

Safer skies overall: just one fatal passenger crash in nearly a decade
Not only are U.S. airline passengers far safer from microbursts than they were decades ago, but they’ve been remarkably safe from other weather hazards—and just about all hazards, for that matter. On August 27, 2006, all 47 passengers aboard a Delta Connection flight were killed in a crash at the Blue Grass Airport near Lexington, KY, that was attributed to pilot error. Since then, there has only been one fatal accident on a U.S. passenger plane: a Continental Connection flight that crashed near Buffalo, NY, on February 12, 2009, killing all 45 passengers. This crash was also attributed to pilot error. For the nation to go nearly a decade with just one fatal accident on U.S. passenger planes would have been unthinkable as recently as the 1990s, when fatalities were a near-annual occurrence.

Americans are also much safer on the road: highway deaths are down by close to 20,000 per year compared to the 1970s and by about 10,000 per year compared to the 1990s. Unfortunately, a big spike occurred in 2015, when traffic deaths rose by an estimated 8% over the previous year, equating to some 2800 additional deaths. This was the largest year-over-year percentage increase in 50 years, according to the National Safety Council. While we don’t know exactly what caused this spike (increased traffic and growing phone-related distraction are possibilities), we do know that weather continues to be a major factor in highway safety. Roughly 3400 people are killed each year when driving in rain, and roughly 5700 on wet roads, according to the Federal Highway Administration.

The take-home message for travelers this summer: don’t worry too much about weather hazards if you’re a passenger on a commercial flight--but when you’re on the road, do everything that you can to drive safely and defensively, especially during adverse conditions. That text message can wait!

I'll be back with a new post by Friday afternoon, including updates on the tropical cyclone likely to form off the coast of Mexico in the next few days and the potential for very heavy rains across the Central Plains and Midwest into next week. PS: If you're hearing claims of "unprecedented" jet stream flow from the Northern to the Southern Hemisphere, check out the excellent debunking just published by Jason Samenow at Capital Weather Gang.

Bob Henson

Aviation Severe Weather

A Gallery of Tropical Influences: MJO, CCKW, TIW, and La Niña

By: Bob Henson , 3:38 PM GMT on June 28, 2016

Given the quick start we’ve seen to the 2016 Atlantic hurricane season--with Tropical Storms Danielle and Colin the earliest third and fourth named storms on record--the Atlantic may not need much help working its way well through the alphabet. Even so, this moment of relative quiet is a good time to look at some factors that could help move the process along. One player now approaching is a strong convectively coupled Kelvin wave (CCKW) located near the International Date Line. CCKWs are large but subtle atmospheric impulses, centered on the equator, that roll eastward at 30-40 mph, with showers and thunderstorms typically along their forward flank. When an eastward-moving CCKW encounters a tropical wave in the Atlantic, the enhanced moisture and upward motion may give it a boost and help it consolidate into a tropical cyclone. For more background on CCKWs, see our post from last July, “Danny’s Leg Up: A Convectively Coupled Kelvin Wave.”


Figure 1. Schematic cross section through a convectively coupled Kelvin wave (CCKW). Image credit: Michael Ventrice.

A CCKW worth watching
The CCKW now in the central Pacific is the strongest that expert Michael Ventrice (The Weather Company) has seen in almost a decade of researching these waves. While passing through the Indian Ocean in mid-June, this CCKW produced near-equatorial westerlies of up to 30 knots (35 mph). This CCKW will be moving into the far eastern Pacific over the next few days. Although Ventrice doubts that this CCKW will maintain its strength as it moves into this area, it still could enhance the odds of tropical cyclone development in the eastern Pacific into the first week of July, as noted in a NOAA discussion on Monday. WU member Levi Cowan (tropicaltidbits.com) observed on Monday that long-range GFS ensemble runs have been unusually consistent in developing a strong tropical cyclone during the first week of July southwest of Mexico. The 8 AM EDT Tuesday tropical weather outlook from the National Hurricane Center gives an area of disturbed weather now along the west coast of Costa Rica a 30% chance of gradual development by next Sunday, July 3, as it moves into the eastern North Pacific well south of Mexico.

The CCKW’s influence may also extend northward to favor development in the Bay of Campeche and/or western Gulf of Mexico. Last week, a few ensemble members from long-range GEFS runs flagged this area for possible development in early July, but the location and strength of the potential tropical cyclone varied greatly from run to run and across ensemble members. The “ghost storm” has since disappeared from more recent GFS runs. (In a Facebook post last Thursday, the NWS office in Tallahassee pointed out the hazard of fixating on a single long-range solution from an ensemble.)


Figure 2. Predicted state of the Madden-Julian Oscillation through mid-July (top to bottom), with the tropical Indian Ocean at left and the eastern tropical Atlantic at right. Bluish colors denote an active phase, favoring showers and thunderstorms (convection) and tropical cyclone formation; red colors show a tendency for convection to be suppressed. The graphics are based on recent conditions (top panel), ECMWF ensemble forecasts (second and third panels), and extrapolation (fourth panel). Image credit: Michael Ventrice, The Weather Company.


Another traveling feature that can influence the Atlantic is the Madden-Julian Oscillation. Typically stronger and much slower-moving than a CCKW, an active MJO phase can favor upward motion and tropical cyclone development for a week or two as its forward flank approaches an ocean basin. MJOs can reinforce or dampen the effects of a CCKW. Ventrice notes: “Usually, the MJO will act to enhance the higher-frequency waves traveling through it. So you will get stronger CCKWs within the active envelope of the MJO and vice versa.” As of last week, the nearest active MJO phase was located over the Maritime Continent, a location that typically works against tropical cyclone development in the western part of the Atlantic basin. It will be a couple of weeks until this MJO makes it far enough east to boost conditions in the Gulf of Mexico, and its strength at that point is still uncertain (see Figure 2). Hurricanes in the Gulf of Mexico and western Caribbean are several times more likely to form during an active MJO phase as opposed to a suppressed phase.

Looking further ahead, the smart money remains on La Niña arriving by autumn, just in time to serve as a favorable influence for tropical cyclones in the Atlantic. Sea surface temperatures in the eastern equatorial Pacific, as tracked by the Niño3.4 index, plummeted from strong El Niño territory in March (departures from normal of greater than +1.5°C) to slightly below-average values in early June, which prompted NOAA to declare an end to the 2015-16 El Niño event. The shift toward La Niña should lead to reduced vertical wind shear over the Atlantic, thus favoring a greater amount of tropical cyclone development.


Figure 3. Departures from the seasonal average of sea surface height (SSH) as measured by NASA satellites on June 8, 1998, and June 9, 2016. Red and white areas denote higher-than-average SSH, which corresponds to warmer-than-average water in the uppermost part of the ocean. Although the El Niño events of 1997-98 and 2015-16 were roughly comparable in timing and strength, the transition toward La Niña was much more advanced at this point in 1998 in terms of cooler-than-average water along the equatorial Pacific. Image credit: NASA/JPL/Caltech.


Figure 4. Departures from the seasonal norm for sea surface temperatures in the Niño3.4 region of the eastern tropical Pacific for April-June 2016. The decrease in SSTs this spring has been marked by large variability, especially in June. Image credit: tropicaltidbits.com.

Is La Niña having second thoughts?
The ongoing transition toward an expected La Niña has been a bit quirky this month. In response to a Western Hemisphere MJO passage, trade winds in early June were unusually weak over much of the eastern tropical Pacific, which runs counter to the La Niña mold. Moreover, the region of cooler-than-average SSTs along the equator is very weak and narrow compared to this point in 1998, when the last “super” El Niño transitioned to La Niña (see Figure 3). The latest weekly Niño3.4 value is -0.4°C, compared to -1.1°C at the same point in June 1998. Another oddity: the daily values of Niño3.4 spiked back above +0.5°C for nearly a week in mid-June, then sank back into negative territory in a matter of days (see Figure 4).

This last quirk may be related to a picturesque feature called tropical instability waves, or TIW. These waves often develop across the eastern equatorial Pacific in northern summer and fall, especially during the onset of La Niña, when SST contrasts are heightened between the equatorial and subtropical regions. The sharp contrast, together with shear produced by contrasting ocean currents, can lead to a line of eddy-like features straddling the equator and marching westward, with a typical separation of about 700 miles (1100 km) between each wave (see Figure 5). Overall, TIW can have a dampening effect on La Niña events, as confirmed in a high-resolution modeling study led by Yukiko Imade (University of Tokyo). In addition, Ventrice notes that the TAO/TRITON buoys that monitor SST across the tropical Pacific have an east-to-west spacing of 15° of longitude, or about 1000 miles (1600 km). According to Ventrice, the wavelength of the TIW and the buoy spacing can sometimes be similar enough to allow regional SST reports to rise and fall in unison over very short periods when the TIW are especially active, as was the case this month (see Figure 6).


Figure 5. Departures from the seasonal average in SSTs across the eastern Pacific at 18Z Friday, June 24, 2016, reveal a sequence of tropical instability waves (TIW) straddling the equator. Image credit: earth.nullschool.net.


Figure 6. For the 7-day period from 12Z June 17, 2016, to 12Z June 24, sea surface temperatures rose and fell in a distinct wavelike pattern across the eastern tropical Pacific, showing the influence of tropical instability waves. Image credit: tropicaltidbits.com.

The bottom line
Despite its unorthodox entrance cues, La Niña is very likely still on its way. One strong sign: just below the surface of the equatorial Pacific, there is still a large area of cooler-than-normal water dominating the topmost 200 meters (660 feet). Any downwelling at the surface would more likely postpone or weaken an impending La Niña rather than quash it. Moreover, an impressive surge of trade winds now across the central/eastern Pacific is expected to force a period of enhanced upwelling in the eastern Pacific that’s likely to boost the evolving La Nina event, according to Ventrice.

Climatology also supports the switch away from El Niño. Going back to 1950, the longest continuous El Niño episode was the 15 overlapping three-month periods from March-May 1982 to May-July 1983. As of March-May 2016, we’re already up to 14 overlapping three-month periods, so if El Niño were to hang on another few months, we would be in record territory.

Meanwhile, the Pacific Decadal Oscillation continues to hum along in a strongly positive mode, with last month’s value of +2.35 the highest for any May in records going back to 1900. Strongly positive PDOs are correlated with more/stronger El Niño events and fewer/weaker La Niña events (although there is a chicken-or-egg factor here, as El Niño and La Niña events themselves feed into the PDO).

We’ll be back with a new post on Thursday.

Bob Henson


La Niña MJO CCKW Hurricane Tropical Meteorology

West Virginia in Shock after Flash Floods Kill At Least 23

By: Bob Henson , 3:09 PM GMT on June 27, 2016

One of the worst flood disasters in West Virginia history has left thousands without power, ruined hundreds of homes, and taken at least 23 lives (Sunday’s toll was lowered on Monday morning after two missing people were found alive). The floodwaters coursed through several valley towns in southeastern WV from late Thursday into Friday after multiple lines of heavy thunderstorms “trained” through the area along a stalled frontal boundary. The first wave of storms arrived Thursday morning after having ripped through the Midwest overnight with high winds and more than a dozen tornadoes. Damage and injury from that severe weather ended up less than expected, whereas the West Virginia flooding was far worse than anticipated, although a flash flood watch was issued by the National Weather Service a day in advance. At least 500 homes were destroyed or severely damaged in Roane County alone, according to the WV Division of Homeland Security and Emergency Management. Neighboring Greenbrier County was also very hard hit, especially the small town of Rainelle, where at least 15 people died. The flood damage extended to the Old White TPC golf course in White Sulphur Springs, home of the annual PGA Tour’s Greenbrier Classic golf tournament. This year’s tournament, which had been scheduled for July 7-10, has been cancelled. Power remained out for more than 10,000 people on Sunday afternoon, three days after the flood began.

A flash flood watch is in effect Monday for a large swath of southern WV and neighboring areas. Although widespread heavy rains are not expected to recur, even localized downpours could exacerbate problems in the worst-hit places. Ominously, a flash flood warning was issued for Summers and Greenbrier Counties at 10:56 AM EDT, as showers and thunderstorms were already expanding in that area with intensification expected this afternoon.


Figure 1. Mark Lester cleans out a box with creek water as he cleans up from severe flooding in White Sulphur Springs, W. Va., Friday, June 24, 2016. Image credit: AP Photo/Steve Helber.


Figure 2. Jay Bennett, left, and step-son Easton Phillips survey the damage to a neighbor’s car in front of their home damaged by floodwaters as the cleanup begins from severe flooding in White Sulphur Springs, W. Va., Friday, June 24, 2016. Image credit: AP Photo/Steve Helber.


Figure 3. Numerous bands of thunderstorms rolled east-southeast across the heart of West Virginia, as shown here in NWS NEXRAD radar imagery from 1729Z (1:29 pm EDT) Thursday, June 23, 2016. Reds and oranges indicate the highest reflectivities and heaviest rain. Image credit: NCAR/RAL Real-Time Weather Data.


Climate change is making the heaviest one-day rains heavier
Rainfall totals for the 48-hour period spanning the flood event ranged as high as 9.65” in Greenbrier County. Most of that likely fell within just a few hours, according to the NWS/Charleston (WV) office. This is not far below the state’s official 24-hour rainfall record of 12.02”, recorded at Brushy Run on June 18, 1949. An unofficial total of 19.00” was measured on July 18, 1889 at Rockport as a hurricane passed to the southeast. The remnants of another tropical cyclone, 1985’s Hurricane Juan, led to West Virginia’s most damaging and second-deadliest flood of record, the Election Day floods in November 1985 that killed 38, ranking behind only the catastrophic Buffalo Creek flood (see below).

Based on radar and other data, Tye Parbyzok (MetStat) estimates that the highest 24-hour rainfall amounts observed in West Virginia last week would be expected to recur less than once every 1000 years on average (see Figure 2). A growing body of research shows that the ever-increasing amount of greenhouse gas in the atmosphere is intensifying the heaviest rainfalls observed in many parts of the world, and models indicate this trend will continue. According to one study highlighted in the 2014 U.S. Climate Change Assessment, a two-day rainfall that might have occurred only once every five years in the early 20th century has become almost 40% more frequent since then, with the greatest increase in the Northeast, Midwest, and Upper Great Plains. The amount of precipitation falling on the wettest 1 percent of days increased by 71% in the Northeast, including West Virginia, from 1958 to 2012. Climate-related trends in flooding are more difficult to assess, since flooding depends on land-use practices as well as atmospheric variables. The beta website Climate Signals has a page devoted to climate-change factors relevant to the West Virginia floods.


Figure 4. Maximum 24-hour recurrence intervals for rainfall from 9:00 pm EDT Tuesday, June 21, through 8 pm EDT Friday, June 24. A swath of southern West Virginia experienced 24-hour rainfalls that would be expected to recur less than once every 1000 years. MetStat computed the recurrence interval statistics based on gauge-adjusted radar precipitation and frequency estimates from NOAA Atlas 14 Volume 8, published in 2013. MetStat provides free access to their near real-time precipitation ARI analyses at their website and Facebook page. Image credit: MetStat, Inc.

U.S. flood toll is running high in the 2010s
Based on its single-state toll, West Virginia’s flash flood is the nation’s deadliest in a number of years. Flash floods are notorious for taking only a few lives at a time, which obscures their cumulative impact on the nation. Last year was a particularly tragic example, thanks in large part to relentless onslaughts of heavy rain and resulting flash floods and river floods in Texas, Oklahoma, and Missouri. In the National Weather Service database of severe weather fatalities (which counts flash and river flood deaths separately from hurricane fatalities), flash and river floods killed 176 people in the United States in 2015. That statistic got little notice, but it’s in fact the largest such total in more than 30 years, ever since 204 lives were lost in 1985. Over the decade 2006-2015, a total of 844 people were killed in U.S. flash floods and river floods, with more than 100 lives lost in 2010 and again in 2011. Disconcertingly, more than half of the past decade’s flood deaths (a total of 446) occurred in vehicles, despite the growing use of the NWS mantra “Turn Around, Don’t Drown.”

2015: 176 deaths, 112 in vehicles
2014: 38 deaths, 16 in vehicles
2013: 82 deaths, 37 in vehicles
2012: 29 deaths, 11 in vehicles
2011: 113 deaths, 68 in vehicles
2010: 103 deaths, 45 in vehicles
2009: 56 deaths, 33 in vehicles
2008: 82 deaths, 39 in vehicles
2007: 89 deaths, 51 in vehicles
2006: 76 deaths, 34 in vehicles
Total: 844 deaths, 446 in vehicles

West Virginia’s tragic flood history
Last week’s flooding hit a state that could use a break. The rise of much-needed alternative forms of energy has brought hard times to the coal industry, and it’s likely that no state has been more affected than West Virginia. Yet the coal industry also played a major role in the state’s deadliest flood on record: the Buffalo Creek disaster of February 26, 1972. After days of heavy rain, a dam built atop coal slurry failed catastrophically above the town of Saunders, with the resulting wave of coal-blackened, sludgy water overtaking two other dams before cascading into more than a dozen unincorporated settlements downstream. In less than an hour, the flood wave swept through the valley, killing 125 people and injuring more than 1100, with some 500 homes destroyed. Although several commissions pinned the blame for the disaster on practices of the Pottstown Coal Company, no indictments were returned and the company settled with the state for a fraction of the damages originally sought. The state’s Division of Culture and History has a moving website devoted to the disaster, which was explored by sociologist Kai Erickson in the 1978 book Everything In Its Path: Destruction of Community in the Buffalo Creek Flood. The website’s final page includes the names and ages of each victim, which serves as especially poignant testimony to this calamity--as does the 1975 film “The Buffalo Creek Flood: An Act of Man,” which is excerpted in the YouTube clip below, from the Kentucky-based Appalshop media center.

Bob Henson


Flood Climate Change

An Exceptionally Slow-Starting Typhoon Season; 95L Fizzles

By: Jeff Masters and Bob Henson , 4:25 PM GMT on June 24, 2016

Residents of the Northwest Pacific have enjoyed an unusually late start to the typhoon season this year, despite the fact that ocean temperatures have been running about 1°C (1.8°F) above average. Though there has already been one tropical depression, the basin has yet to see a named storm. Typically, 90% of all Northwest Pacific seasons see their first named storm by May 1 (thanks to Mike Fiorino for this stat.) Four named storms, two typhoons, and one intense typhoon typically occur by June 24; last year, we'd already had three Category 5 typhoons by mid-June!


Figure 1. One of 2015's early-season Category 5 typhoons: Typhoon Maysak as seen from the International Space Station at 2118Z (5:18 pm EDT) on March 31, 2015. Image credit: Terry Virts/NASA/ISS

This year is only the sixth time since 1950 that the first tropical storm of the Northwest Pacific season has occurred after June 1:

1998: July 8 start date
1973: July 1 start date
1983: June 25 start date
2016: June 24 and counting…
1952: June 10 start date
1984: June 9 start date

The four years with the latest start dates—including 2016—all occurred during the transition from strong El Niño conditions to neutral or La Niña conditions later in the year.  The upper-level atmospheric circulation associated with this transition bring conditions which discourage tropical cyclones--sinking air, surface high pressure, and dry conditions--to the typhoon breeding grounds of the Northwest Pacific. Surface pressures over the past month in the waters east of the Philippines extending to the Date Line have been 0.5 - 1.5 mb above average over the past two months (Figure 1). The Friday morning Tropical Weather Discussion for the Northwest Pacific from the Joint Typhoon Warning Center highlighted just one area of low concern, and the GFS and European models showed nothing developing for at least the next five days.


Figure 2. Surface pressures between May 1 - June 22, 2016, in the waters of the Northwest Pacific east of the Philippines (extending to the Date Line) have been 0.5 - 1.5 mb above average. Image credit: NOAA/ESRL.

A slow start usually a harbinger of a quiet typhoon season
This year's slow start to typhoon season is likely a harbinger of a season that will be much below-average in activity. Slow-starting typhoon seasons like 1998, 1973, and 1983 all had total activity that was much below average: the Accumulated Cyclone Energy (ACE) in those years were 152, 220, and 147--well below the average ACE from the past 51 years of 298. The May 7 forecast for the 2016 Northwest Pacific typhoon season made by British private forecasting firm Tropical Storm Risk, Inc. (TSR) called for a below-active season with 22 named storms, 13 Category 1 or stronger typhoons, 6 major Category 3 or stronger typhoons, and an Accumulated Cyclone Energy (ACE) of 217. The long-term averages for the past 51 years are 26 named storms, 16 typhoons, 9 major typhoons, and an ACE of 298. TSR rates their skill level as modest for these late May forecasts--13% to 30% higher than a "no-skill" forecast made using climatology.

Quiet start to year in Northeast Pacific as well
The hurricane season hasn’t exactly been hopping on the eastern side of the Pacific either. We have seen only one named storm anywhere east of the International Date Line in 2016: Hurricane Pali, which hit Category 2 strength in mid-January. Pali was the earliest named storm and earliest hurricane on record in the Central or Eastern Pacific (reliable satellite-based records only go back to 1971). One could argue it was an “overflow” storm from the extremely busy 2015 season rather than a true kickoff to the 2016 season.

Despite the slow start to their core tropical season, it’s still possible that the Central and Eastern Pacific will catch up later in the year. Sea surface temperatures remain slightly above average across most of the region south and southwest of Mexico where Eastern Pacific tropical cyclones tend to develop.  The forecast for the 2016 Eastern Pacific hurricane season, issued on May 6 by Mexico's Servicio Meteorológico Nacional (SMN), predicted 17 named storms, 9 hurricanes, and 4 major hurricanes. This is close to the average numbers (east of 140°W) from 1981 - 2010, which were 15 named storms, 8 hurricanes, and 4 major hurricanes. Similarly, in its outlook issued May 27, NOAA predicted that a near-average season would be the most likely outcome in the Eastern Pacific, with a 70% chance of 13-20 named storms, 6-11 hurricanes, and 3-6 major hurricanes. The 2015 Northeast Pacific hurricane season (east of 140°W) featured 18 named storms, 13 hurricanes, and 9 major hurricanes.

The transition from El Niño to La Niña may have a larger effect on the Central than the Northeast Pacific. About half as many named storms form in the Central Pacific between 120°W and 180°W in a La Niña year, compared to an El Niño year. Hawaii is about three times less likely to be impacted by a tropical cyclone in a La Niña vs. an El Niño year, according to Phil Klotzbach (Colorado State University].


Figure 3. Accumulated cyclone energy (ACE) by year for all tropical cyclones in the Northern Hemisphere from January 16 to June 23. Image credit: Phil Klotzbach.

Northern Hemisphere: off to an extremely slow start
This year’s quietude across the Pacific has led to an exceptionally low amount of accumulated cyclone energy in the Northern Hemisphere for the year to date. The contrast with 2015 couldn’t be starker: as pointed out by Phil Klotzbach, the Northern Hemisphere ACE from January 16 to June 23 was the highest on record in 2015 and the lowest on record in 2016. The low ACE is primarily due to the delayed start of the Northwest Pacific season; that basin accounts for nearly two-thirds of Northern Hemisphere ACE up to this point in a typical year, compared to about 2% coming from the Atlantic. The North Atlantic is at a record-setting pace for named storms, with four already observed to date. However, Tropical Storms Bonnie, Colin, and Danielle were all short-lived systems with peak sustained winds of 50 mph or less. January’s off-season Hurricane Alex produced more ACE than these three storms combined.

Phil Klotzbach’s excellent new website for real-time tropical cyclone statistics has a "Basin Archives" button with historical statistics for those wanting more information.


Figure 4. Latest satellite image of Invest 95L over the Gulf of Mexico.

95L in the Southern Gulf of Mexico a low threat to develop
A tropical disturbance over the southern Gulf of Mexico (Invest 95L) has grown less organized since Thursday, and no longer appears to be a threat to develop into a tropical depression. Satellite loops late Friday morning showed 95L had only a limited amount heavy thunderstorms, which were poorly organized and had no signs of rotation. The Air Force hurricane hunter mission scheduled for Friday was cancelled. 95L is expected to move ashore over Mexico between Veracruz and Tampico on Saturday, bringing heavy rains of 2 - 4". In their 8 am EDT Friday Tropical Weather Outlook, NHC gave 95L 2-day and 5-day development odds of 10%. The next name on the Atlantic list of named storms is Earl, but don't expect it to get used for 95L.

None of our reliable models for tropical cyclone genesis are showing anything developing in the Atlantic through at least June 29.

Have a great weekend, everyone!

Jeff Masters and Bob Henson

Hurricane

At Least 78 Deaths in China Tornado; Midwest Dodges Major Damage

By: Bob Henson , 4:29 PM GMT on June 23, 2016

A tornado struck the outskirts of the east-central Chinese city of Yancheng during a powerful thunderstorm on Thursday afternoon, killing at least 78 people and causing widespread destruction. Yancheng is an urban area of more than 8 million people with a city-center population of about 1.6 million, located in the coastal plain of China’s Jiangsu Province about 200 miles north of Shanghai. Chinese state media are reporting nearly 500 injuries, with 200 critical. The storm also produced hail and heavy rain.


Figure 1. Residents pass houses destroyed in the aftermath of a tornado that hit Funing county, in Yancheng city in eastern China's Jiangsu Province on Thursday, June 23, 2016. A powerful tornado killed dozens and destroyed large numbers of buildings Thursday in the eastern Chinese province of Jiangsu, state media reported. Image credit: Color China Photo via AP.


Figure 2. A villager stands near houses destroyed in the aftermath of a tornado that hit Funing county in Yancheng city in eastern China's Jiangsu Province on Thursday, June 23, 2016. Image credit: Color China Photo via AP.


Figure 3. Himiwari-8 satellite image from 0600Z on June 23, 2016 (2:00 am Thursday EDT, or 2:00 pm Thursday local time in Yancheng, China). A band of intense thunderstorms stretched more than 600 miles across central and northeastern China. The apparent tornado struck the Yancheng area around 2:30 pm local time Thursday. The coldest cloud tops associated with the Yancheng thunderstorm (blue and green colors] span about 250 to 300 miles (400-480 km]. Image credit: CSU/CIRA/RAMMB, courtesy Japanese Meteorological Agency.

Another deadly result of the Mei-yu front
Intense storms are common along the Mei-yu (or baiu) front, which typically persists for a few weeks in late spring and early summer. This semi-permanent feature extends from eastern China across Taiwan into the Pacific south of Japan, associated with the southwest monsoon that pushes northward each spring and summer. The AMS Glossary notes: “The mei-yu/baiu front is very significant in the weather and climate of southeast Asia as it serves as the focus for persistent heavy convective rainfall associated with mesoscale convective complexes (MCCs) or mesoscale convective systems (MCSs) that propagate eastward.” A number of studies have found that the Mei-yu rainfall tends to be particularly heavy in the summer following an El Niño event.

On June 1, 2015, China experienced its worst peacetime maritime disaster on record, as 442 people died when a cruise ship capsized on the Yangtze River during an intense Mei-yu thunderstorm. Although a tornado struck about five miles away, an official report found that a strong microburst was most likely responsible for the capsizing. Similarly, it may take time to determine how much of the damage in Yancheng was related to tornadic activity as opposed to any downbursts that may have occurred. As shown in the map below, eastern China is one of the more tornado-prone parts of Eurasia.


Figure 4. The relative likelihood that the atmosphere would support tornado production within grid boxes of 2° latitude and longitude, as estimated from model-generated atmospheric profiles. The scale is logarithmic; a value of -2.0 (orange) corresponds to 15 six-hour periods per year that are tornado-favorable, and the likelihood increases or decreases by a factor of 10 for every change of 1.0 on the axis at bottom. Image credit: Courtesy Harold Brooks, NOAA National Severe Storms Laboratory. An earlier version of this graphic appears in Brooks et al., “The spatial distribution of severe thunderstorm and tornado environments from global reanalysis data,” Atmospheric Research 67-68 (2003).

Widespread wind damage from Wednesday night’s storms
NOAA’s Storm Prediction Center has logged more than 130 preliminary reports of high wind stretching from Illinois to North Carolina in the wake of a fast-moving thunderstorm complex that swept along a surface front parallel to a strong upper-level jet stream late Wednesday. Although far-flung, the high-wind episode does not appear to have been exceptionally destructive. In order to place an event as a derecho in the NWS Storm Data archive, wind damage and/or wind gusts of at least 50 knots (57 mph) must extend along a band at least 250 miles long, with at least three reports of gusts reaching 65 knots (74 mph) separated by at least 40 miles. Most of the reports on the SPC log do not yet indicate wind speeds, so we don’t yet know if this event’s winds will be strong enough to qualify. The number of wind reports is also on the low side for a derecho, according to Jon Erdman (weather.com). As of late Thursday morning, SPC logged 19 preliminary tornado reports, all from a string of supercell storms that intensified just before nightfall across north-central Illinois. No major damage or injuries were reported from the twisters, although one storm chaser drove directly into a tornado.


Figure 5. Reports of severe weather logged by the NOAA/NWS Storm Prediction Center as of 11:44 AM CDT Thursday, June 21, 2016, for the period from 8:00 AM CDT Wednesday through 8:00 AM CDT Thursday.

The most intense storms on Wednesday were suppressed until late afternoon by a cap of very warm air several miles above the surface. Once they formed, they congealed fairly quickly into a broken area of severe storms (see embedded tweet at bottom) that produced lots of wind and heavy rain but not much large hail. There were just 14 reports of severe hail on Wednesday, with only three reports of hail of at least 2” diameter (and those were from storms in Minnesota separate from the fast-moving complex later that night).

More severe weather is on the agenda for Thursday, although the odds of significant severe storms appear a bit lower than on Wednesday. NOAA/SPC has placed parts of the central Appalachians and upper Ohio Valley under an enhanced risk of severe weather for Thursday afternoon and evening, with a slight risk extending from most of Kentucky to the Virginia/North Carolina coast. A few severe storms may also pop up in eastern Colorado. On Friday and Saturday, a strong upper-level low moving across southern Canada may generate intense storms along a cold front as it moves from Montana to Minnesota.


Figure 6. Infrared satellite image of Invest 95L in the northwest Caribbean at 1615Z (12:15 PM EDT] Thursday, June 23, 2016. Image credit: NOAA/NESDIS.

Invest 95L forms in northwest Caribbean
A disorganized area of disturbed weather moving slowly through the northwest Caribbean was designated as Invest 95L on Thursday morning. The disturbance is pushing heavy rains toward northern Belize and the southeastern Yucatan Peninsula of Mexico. There's no time for 95L to develop much before it moves ashore, but it may have a brief window to organize somewhat on Friday during a short westward trek across the southern Bay of Campeche. A sprawling upper-level ridge over the southern United States should inhibit 95L from making any dramatic moves northward toward the Gulf of Mexico. In its 8 AM EDT Thursday tropical weather outlook, the NOAA National Hurricane Center gave 95L a 10% chance of development over the next two to five days.

We'll be taking a closer look on Friday at short- and long-term prospects for tropical cyclone development in the Gulf of Mexico and Caribbean.

Bob Henson



Tornado Severe Weather Extreme Weather

Tornado and Derecho Threat from Midwest to Appalachians

By: Bob Henson , 4:49 PM GMT on June 22, 2016

A near-classic early-summer sequence of potentially tornadic storms followed by destructive straight-line winds is in the cards for the Midwest on Wednesday afternoon and evening, with the wind-packing storms possibly approaching the mid-Atlantic states on Thursday morning. In its Day 1 outlook updated at 12:30 PM EDT Wednesday, NOAA’s Storm Prediction Center is calling for a moderate risk of severe weather (the second highest of SPC’s five risk categories) from northern Illinois into western Ohio. Lesser risk categories extend to the Washington, D.C. area. The event will unfold along a warm front extending east-southeast from a surface low in Iowa through the risk corridor. A very humid, unstable air mass lodged against the front will provide plenty of fuel for severe storms, and a strong jet stream oriented parallel to the front will keep the storms moving at a rapid pace as they eventually congeal into a large mesoscale convective system (MCS).

While there is a real risk of strong tornadoes on Wednesday, especially in and near northern Illinois, an even larger area will be vulnerable to potentially damaging winds produced by the expected MCS. The high-resolution HRRR model suggests a large MCS will be consolidating and pushing rapidly southeast across Ohio around midnight Wednesday night (see Figure 2 below). This MCS may produce a derecho, a large area of thunderstorm-generated high winds that propagates rapidly over distances of 250 miles or more. Longer-range models bring the MCS into West Virginia and Pennsylvania overnight, with the potential for storms moving into or regenerating across the Washington, D.C./Delmarva area on Thursday morning. Depending on how the first batch of storms evolves, another round of severe storms could pop along the front from Kentucky to the mid-Atlantic on Thursday (NOAA/SPC has a slight risk for this area in its Day 2 outlook).


Figure 1. WU depiction of NOAA/SPC severe weather risk areas as of mid-morning Wednesday, June 22, 2016, valid through 8:00 AM EDT Thursday, June 23.


Figure 2. In its run from 14Z (10:00 AM EDT) Wednesday, June 22, 2016, the high-resolution HRRR model depicts a large thunderstorm complex moving rapidly across Ohio at 05Z (1:00 AM EST) Thursday, June 23. Such model predictions are not intended to be exact depictions of where thunderstorms will actually be located. Image credit: www.tropicaltidbits.com

A whopper of a wind-producer
The term “derecho” gained wide notice after an especially powerful one moved from northern Illinois to the mid-Atlantic coast in a matter of hours on June 29-30, 2012 (see Figure 3). That derecho, one of the strongest documented in North America, caused almost $3 billion in damage and took 28 lives. Millions were affected by power outages that lasted for days in some areas, and countless trees were uprooted. At first glance, it might seem that models are painting a scenario for Wednesday night bearing some resemblance to the 2012 pattern. However, that event was fed by low-level heat and moisture unprecedented for late June; only a few hours before the high winds struck, Washington, D.C., had set a monthly record high of 104°F. Surface temperatures along the front won’t be as extreme in this case, which suggests less chance of a similarly potent event. The timing of the upper-level impulse that will propel Wednesday night’s storms is also less favorable for bringing the MCS across the Appalachians before the typical early-morning reduction in atmospheric instability. As shown in Figure 5 below, derechos are much more common from Illinois to Ohio than further east.


Figure 3. Composite radar image showing the progress of the intense derecho that swept from the Chicago area to Washington, D.C. on the night of June 29, 2012. Covering about 600 miles in just 10 hours, the derecho produced hundreds of severe wind gusts, with peak winds of 80 to 100 mph. Image credit: Greg Carbin/NWS Storm Prediction Center.


Figure 4. A thunderstorm complex associated with an incipient derecho moves into LaPorte, Indiana, on the afternoon on June 29, 2012. Image credit: Kevin Gould/NOAA, courtesy NASA Earth Observatory

Tonight’s derecho threat is right down the climatological alley
In a weather.com article published on Wednesday morning, Jon Erdman shows us just how well today’s event lines up with climatology. Erdman spotlights a new study by Corey Guastini and Lance Bosart (University at Albany, State University of New York), published in the April 2016 issue of Monthly Weather Review, that examines 256 U.S. warm-season derechos between 1996 and 2013. Figure 5 below shows the preferred corridor, extending from northern Illinois to Ohio, with much less frequent activity further east. “Northeastern Illinois is ground zero for warm-season progressive derechos," Bosart said.


Figure 5. The number of derechos observed within 10,000-square-kilometer boxes (about 60 by 60 miles) during the May-August interval from 1996 to 2013. Image credit: Corey T. Guastini and Lance F. Bosart, Analysis of a Progressive Derecho Climatology and Associated Formation Environments. Monthly Weather Review, April 2016, (c) American Meteorological Society.

What exactly is a derecho?
In Spanish, derecho has several meanings, including “straight.” Gustavo Hinrichs adopted the term in 1883 to describe a type of thunderstorm-related wind he dubbed “the straight blow of the prairies." [Derecho contrasts with the Spanish tornar, "to turn," as in a tornado--but we don't know if Hinrichs intended this contrast.] Hinrichs published at least one scientific article on derechoes, but the phenomenon did not get widespread research attention until a century later. Eminent severe storms forecaster Bob Johns played a key role in reviving the concept in a landmark 1987 paper with William Hirt. It was only after reviewing a number of “northwest flow events” that Johns and Hirt discovered and adopted the earlier term. In a 2007 essay, Johns describes how the derecho concept originated and evolved. The current definition of “derecho” in the AMS Glossary is “a widespread convectively induced straight-line windstorm. Specifically, the term is defined as any family of downburst clusters produced by an extratropical mesoscale convective system.” In order to place an event as a derecho in the NWS Storm Data archive, wind damage and/or wind gusts of at least 50 knots (57 mph) must extend along a band at least 250 miles long, with at least three reports of gusts reaching 65 knots (74 mph) separated by at least 40 miles.

In the June 2016 issue of the Bulletin of the American Meteorological Society, SPC’s Stephen Corfidi and colleagues propose narrowing the definition to focus on progressive-type derechos, the ones that carve out a single, well-defined swath of high wind, as opposed to other thunderstorm-driven high wind events that tend to be scattered over larger areas. The latter could be called “squall-line windstorms,” they suggest. “Used in this way, “squall line” would realize a renaissance of sorts; the term also would come to be associated with a more distinct meteorological phenomenon than in years past.”

We’ll be following the severe weather this afternoon and evening in a WU liveblog.

Bob Henson


Severe Weather Tornado Derecho Extreme Weather

Significant Severe Threat for Midwest on Wed; Danielle is Done; SW Still Cooking

By: Bob Henson and Jeff Masters , 4:16 PM GMT on June 21, 2016

Fierce thunderstorms capable of spawning significant tornadoes and very high winds are possible Wednesday afternoon and evening across an east-west corridor that will lie near or across the Chicago area. NOAA’s Storm Prediction Center is predicting a moderate risk of severe weather for Wednesday PM extending from southeast Wisconsin and northeast Illinois to southeast Michigan and northwest Ohio (see Figure 1). “Moderate” is actually the second-highest category in the five-level SPC hierarchy of risk. It’s fairly unusual for SPC to issue such a high threat level on the morning before an event, which speaks to the volatility of the set-up expected to take shape.


Figure 1.. WU depiction of NOAA/SPC severe weather risk areas as of late Tuesday morning, June 21, 2016, valid on Day 1 (left, Tuesday) and Day 2 (right, Wednesday).

Tuesday is “the day before the day,” as a weak surface boundary extending from Nebraska into the Missouri and Ohio Valleys begins edging northward while a powerful upper-level impulse approaches from the west and a surface low organizes in the Central Plains. SPC has slight-risk zones for Tuesday afternoon and evening along the surface boundary from the western Dakotas all the way to the mid-Atlantic. Where and when storms unfold in the Midwest on Tuesday night will help influence the scenario on Wednesday. A mesoscale convective system, or MCS (a large, persistent thunderstorm complex) may develop in South Dakota late Tuesday and move toward the Chicago area overnight, a frequent early-summer track. If this happens, it would leave a boundary of rain-cooled air somewhere just to its south—perhaps reinforcing the current surface boundary—with extensive clouds to its north. Any east-west surface boundaries could serve as focal belts for Wednesday afternoon’s storms, helping to concentrate the low-level “spin” (vorticity) that can feed tornadic supercells. It’s too soon to know exactly where the zone of greatest risk will end up, but the Chicago area is certainly a possibility.

The period of greatest concern is Wednesday afternoon and evening, when the upper-level impulse will approach the Great Lakes and a strong surface low will begin accelerating eastward along the surface boundary. Very rich low-level moisture will be in place, and southeasterly low-level winds will be overtopped by strong westerlies at middle and upper levels. These classic ingredients for supercell thunderstorms are projected by models to reach unusually intense values by late Wednesday. One possible scenario is for one or more long-lived supercell thunderstorms—potentially with significant tornadoes—persisting for several hours, most likely focused over northern Illinois and/or southern Wisconsin into southern Michigan and northern Indiana. These storms might then morph into an MCS that could tear eastward overnight into Ohio and Pennsylvania with very strong surface winds. If the storms consolidate quickly, it is certainly plausible we could have a Wednesday night derecho—a long corridor of damaging surface winds extending over several hours. Derechoes are extremely difficult to predict, as they hinge on dynamic and thermodynamic features that are often not clear until the event is at our doorstep, but the situation certainly bears a close watch.


Figure 2. The 4-km version of the NAM model run at 12Z (8:00 am EDT) Tuesday, June 21, 2016, valid at 9Z (5:00 am EDT) Thursday, June 23, 2016, indicates a large area of thunderstorm-driven winds at 850 mb (about a mile above the surface) exceeding 64 knots (74 mph). In such a situation, high winds would likely mix to the surface in some areas. Any model depiction of thunderstorm activity this far out involves great uncertainty, so this map should be seen not as a literal forecast but as a rough depiction of one of many potential scenarios. Image credit: tropicaltidbits.com.

Although severe weather is typically more frequent further to the south, the Chicago metro area is one of the nation’s most vulnerable to tornadoes and other severe threats. We looked at the potential threat of a violent, long-track tornado in Chicago in the post Big Wind in the Windy City. Victor Gensini, an associate professor of meteorology at the College of DuPage in the Chicago suburb of Glen Ellyn, is quite concerned about Wednesday’s outlook. “I would argue that this forecast severe weather environment is likely the most impressive (at least from an ingredients standpoint) ever to take shape over one of the nation’s biggest three metro areas,” he said in an email. Gensini’s group is planning to launch a special radiosonde on Wednesday afternoon in northern Illinois, where the ingredients may come together in an area poorly sampled by the standard NWS radiosonde network.


Figure 3. Michael Martinez drinks a bottle of water at a Salvation Army hydration station in an effort to beat rising temperatures in Phoenix on Monday, June 20, 2016. Phoenix set daily record highs of 118°F on Sunday and 116°F on Monday, which were the earliest readings above 115°F in city history. Image credit: AP Photo/Ross D. Franklin.

All-time heat record set on Tuesday in Blythe, CA
The atmospheric oven remains set on “high” across the Desert Southwest, where a fresh batch of records was seared into the weather annals on Tuesday. Chief among them was the 124°F at Blythe, CA, breaking the city’s all-time high of 123°F set most recently on July 28, 1995. Records in Blythe go back to 1948. Another standout in the Lower Colorado Valley was the 125°F reading at Needles, CA, the highest temperature ever observed there in June (previous record of 123°F was on June 29, 2013). Tuesday tied with the 125°F observed on July 17, 2015, for the highest temperature ever recorded in Needles, where records go back to 1941. Thanks to WU weather historian Christopher Burt for this tidbit. Needles is often the hottest location in the contiguous U.S., and back on August 14, 2012, Needles had a trace of rainfall at a temperature of 115°F, producing what appears to be a global record for the “hottest rain on Earth.” The hot spot on Monday was Death Valley, CA, which set a new daily high temperature record of 126°F (old record for the date: 125°F in 1961.) On top of these local records, the high temperature in Laughlin, Nevada hit 125°F. If verified, this would be a tie for the hottest temperature ever measured in state--a 125°F reading at Laughlin on June 29, 1994.

The most exceptional aspect of the Southwest heat wave is its location on the calendar, days earlier than similar heat has ever been recorded in many spots. On Wednesday morning, Phoenix scored its earliest low of 90°F on record, beating June 22, 1990. The intense upper-level high in place over the Southwest will be weakening slightly as the week rolls on, so this particular heat wave may have now crested, although excessive heat warnings continue in place for much of southeast CA, southwest AZ, and southern NV. Even with the heavy media attention paid to the hazards of this heat wave, it has taken an unfortunate toll: at least five people died from the heat on Sunday in Arizona. Several were young, in-shape hikers or bikers, a reminder that heat exhaustion and heat stroke can affect anyone, especially those without adequate access to water.

Another byproduct of the record heat atop multiyear drought is increased fire risk. Two major fires broke out on Monday very near each other in Azusa and Duarte, just north of the heavily populated San Gabriel Valley about 25 miles east of Los Angeles. The uncontained fires had grown to 5400 acres by Tuesday morning, prompting evacuations of more than 750 nearby residents.


Figure 4. Smoke from wildfires burning in Angeles National Forest fills the sky behind the Los Angeles skyline on Monday, June 20, 2016. Located several miles apart, the wildfires devoured hundreds of acres of brush on steep slopes above foothill suburbs erupted in Southern California as an intensifying heat wave stretching from the West Coast to New Mexico blistered the region with triple-digit temperatures. Image credit: AP Photo/Ringo H.W. Chiu

Danielle dissipates after making landfall as a 40 mph tropical storm
Tropical Storm Danielle made landfall near 7 pm CDT Monday ten miles north of Tuxpan, Mexico as a tropical storm with 40 mph winds. The rugged terrain of Mexico severely disrupted the storm, and Danielle dissipated early Tuesday morning. Lingering moisture from Danielle will continue to affect Mexico, bringing some areas of total rainfall amounts of 8 - 12" along the coast between Tampico and Veracruz, causing dangerous flash flooding and mudslides through Tuesday evening. So far, the highest rainfall amounts appear to be the  8+ inches that have fallen at Pozo Rica de Hidalgo; Tuxpan received 4.98", and Puebla, 5.33". No significant damages or casualties have been reported from the storm thus far. Danielle was a tropical storm for just twelve hours. Danielle's formation date of June 20 was the earliest appearance on record for the Atlantic's fourth named storm of the season; the previous record was June 23, 2012, when Tropical Storm Debby formed.

The tropical Atlantic looks like it will be quiet for the remainder of the week, with none of our reliable tropical cyclone genesis models showing anything developing.

Bob Henson and Jeff Masters


Figure 5. Tropical Storm Danielle nearing landfall on Monday afternoon, June 20, 2016, as seen by NASA's Aqua satellite. At landfall, Danielle had top sustained winds of 40 mph. Image credit: NASA.

Severe Weather Hurricane Heat Extreme Weather

Danielle the Atlantic's Earliest 4th Storm on Record; 115°-120° Heat in SW U.S.

By: Jeff Masters and Bob Henson , 3:59 PM GMT on June 20, 2016

Tropical Storm Danielle formed on Monday morning in the Gulf of Mexico's Bay of Campeche, but won't be around long. The storm's west to west-northwest motion will carry the storm inland over Mexico between Veracruz and Tampico by Monday evening. With top winds of just 45 mph as estimated by the National Hurricane Center in their 11 am EDT Monday advisory, heavy rain is expected to be the primary threat from the storm. Satellite loops show a large area of intense thunderstorms with heavy rain are moving inland along the Mexican coast south of Texas, and total rainfall amounts of 6 - 10" are likely to cause dangerous flash flooding and mudslides in the mountainous terrain along the coast. Heavy rains from Danielle will remain just south of Texas, with Brownsville expected to pick up an inch of rain or less in scattered thunderstorms through Monday night. Danielle will dissipate by Tuesday over the rugged terrain east of Mexico City.


Figure 1. Latest satellite image of Danielle.

Danielle the Atlantic's earliest fourth named storm on record
Danielle's formation marks the earliest appearance on record for the Atlantic's fourth named storm of the season; the previous record was June 23, 2012, when Tropical Storm Debby formed. However, as wunderground member Neapolitan pointed out in the comments of our previous blog post, a lot of early storm activity is not a sure sign that there'll be a lot of late storm activity. For instance, 2011 saw fifteen named storms before the traditional September 10 - 11 halfway point of the hurricane season: one in June, three in July, eight in August, and three in early September. Some people thought the year might end with up to 30 storms--but just two more storms formed in late September, one in October, and one in November, giving a season total of nineteen. Rather than a 50/50 split between the front and back halves of the season, the ratio was 78/22. Generally, high early season activity is only a harbinger of an active Atlantic hurricane season when the early season activity occurs in the Caribbean or tropical Atlantic. This has not been the case in 2016.


Figure 2. Helicopter-related firefighting efforts were limited on Sunday at the uncontained Brown Fire in far south Arizona, which has affected more than 8000 rugged acres in the Baboquivari Mountains southwest of Tucson. Believed to be caused by humans, the fire is now under investigation. Image credit: AZ State Forestry.

Blazing Arizona: Sunday’s heat was the real deal
A well-predicted heat wave crescendoed on Sunday with some of the highest temperatures ever recorded in the larger towns and cities of southern California, Arizona, and northern Mexico. The heat was produced by an extremely strong upper-level high building over the Southwest just one day before the summer solstice, when the amount of incoming solar energy peaks. Sunday was the hottest day observed in any year prior to the summer solstice, and the hottest day on record for so early in the season, in Yuma (120°F, ahead of June 24, 1957), Phoenix (118°F, ahead of June 24, 1929), and Tucson (115°F, ahead of June 25, 1994). Sunday also tied as Phoenix’s 5th hottest day on record, and Yuma’s 5th hottest. In Tucson, only two other days have been officially hotter than Sunday: June 26, 1990 (117°F) and June 29, 1994 (116°F). However, as we reported last week, the instrumentation that was used to measure official temperatures at Tucson International Airport during the early 1990s was later found to be problematic. As a result, weather record researcher Maximiliano Herrera believes that 115°F—measured at the Tuscon NWS office on June 19, 1960; June 26, 1990; and July 28, 1995, as well as on Sunday at the airport—is a more reliable all-time high for Tucson. Herrera also reported that Altar, Mexico had its hottest temperature in recorded history on Sunday--48.5°C (119.3°F), beating the previous record of 48.3°C set in 1985. The award for the hottest place on Earth on Sunday may go to Piedra, Arizona, southwest of Phoenix, where the high temperature hit a remarkable 127°F (52.8°C). Thanks go to weather records researcher Jérôme Reynaud for this info (he maintains a database of all locations on Earth that have exceeded 50°C so far in 2016.) If confirmed, this would rank as the second hottest temperature ever measured in Arizona, and the hottest temperature measured anywhere on Earth so far in 2016. Stanwix, Arizona, about 8 miles to the west of Piedra, hit 125°F on Sunday.

Excessive heat warnings continued to plaster the far Southwest on Monday, as some areas were expected to inch even hotter while others could wind up just a shade less scorching. The warnings included Los Angeles, San Diego, Las Vegas, Phoenix, and Tucson. Later this week, a modest amount of moisture will began filtering into the region, bringing down temperatures somewhat but keeping conditions very uncomfortable. The heat will also persist across large swaths of the Plains and Southeast, though it should fall short of record-setting intensity in most areas.

Jeff Masters and Bob Henson

Hurricane Heat

Gulf of Mexico's 94L Close to Tropical Depression Status

By: Jeff Masters , 4:14 PM GMT on June 19, 2016

A tropical disturbance over the southern Gulf of Mexico (Invest 94L) has grown more organized since Saturday, and appears likely to develop into a tropical depression on Sunday or Monday as the storm heads west-northwest at 10 mph. Satellite loops late Sunday morning showed the disturbance had acquired a well-developed surface circulation, but 94L's heavy thunderstorms were not well organized and were relatively sparse, as seen on Mexican radar out of Sabancuy. Development was being arrested by the presence of high wind shear of 20 knots and a large area of dry air to the west, as seen on water vapor satellite images. Sea Surface Temperatures (SSTs) in the southern Gulf of Mexico are very warm, about 29 - 29.5°C (84 - 85°F), which will help development. An Air Force hurricane hunter aircraft will investigate 94L on Sunday afternoon to determine if a tropical depression has formed.


Figure 1. Latest satellite image of Invest 94L over the Gulf of Mexico.


Figure 2. Predicted total rainfall from 94L from the 00Z (8 pm EDT) Saturday June 18, 2016 run of the HWRF model. The model predicted 94L would develop into Tropical Storm Danielle with top winds of 40 - 45 mph and bring widespread rains of 4 - 8" to the coast of Mexico between Veracruz and Tampico, with a few isolated areas getting more than 8". Image credit: NOAA/NCEP.

Forecast for 94L
Steering currents favor a west-northwest motion for 94L across the Bay of Campeche, with landfall occurring between Tampico and Veracruz, Mexico on Monday afternoon or evening. In this region, 3 - 6" of rain are likely Sunday through Tuesday--with higher rainfall amounts of 4 - 8" with isolated 8 - 12" amounts if 94L ends up developing into a tropical storm. The 8 am EDT Sunday run of the SHIPS model predicted that wind shear would fall to the moderate range, 10 - 20 knots, by Sunday afternoon, giving 94L increased chances of development The Sunday morning operational runs of our three reliable models for predicting tropical cyclone genesis, the European, GFS and UKMET models, all supported development of 94L into a tropical depression; more than 80% of the 70 forecasts from the GFS and European model ensembles showed 94L developing into a tropical depression by Monday. In their 8 am EDT Sunday Tropical Weather Outlook, NHC gave 94L 2-day and 5-day development odds of 70%. If 94L becomes a tropical storm, it would be named Danielle. I don't see heavy rains from 94L reaching South Texas.

Jeff Masters

Hurricane

94L May Develop, Bring Heavy Rains to Mexico's Bay of Campeche Coast

By: Jeff Masters , 4:10 PM GMT on June 18, 2016

A tropical disturbance over Mexico's Yucatan Peninsula (Invest 94L) has the potential to develop into a tropical depression on Sunday or Monday over the Gulf of Mexico's Bay of Campeche as the storm heads west-northwest at 10 mph. Satellite loops late Saturday morning showed the disturbance had developed a moderate degree of spin, with a few low-level spiral bands already apparent over the Bay of Campeche; Mexican radar out of Sabancuy showed a few heavy rain showers over the Yucatan Peninsula and adjacent waters. Invest 94L had only a modest amount of heavy thunderstorm activity, and development was being arrested by interaction with land and the presence of high wind shear of 20 - 25 knots. Water vapor satellite images showed a large area of dry air over the western Gulf of Mexico, which was also slowing development. Sea Surface Temperatures (SSTs) in the southern Gulf of Mexico are very warm, about 29 - 29.5°C (84 - 85°F), which will help development. An Air Force hurricane hunter aircraft is on call to investigate 94L on Sunday afternoon.


Figure 1. Latest satellite image of Invest 94L approaching the Gulf of Mexico.

Forecast for 94L
Steering currents favor a west-northwest motion for 94L across the Bay of Campeche, with landfall occurring between Tampico and Veracruz, Mexico on Monday afternoon or evening. In this region, 3 - 6" of rain are likely Sunday through Tuesday--with higher rainfall amounts to be expected if 94L ends up developing into a tropical storm. The 8 am EDT Saturday run of the SHIPS model predicted that wind shear would stay high, 20 - 30 knots, through Sunday night, then fall to the moderate range, 10 - 20 knots, on Monday, giving 94L a better chance to develop then. The Saturday morning operational runs of our three reliable models for predicting tropical cyclone genesis, the European, GFS and UKMET models, had one model--the European--supporting development of 94L into a tropical depression. However, about 40 - 50% of the 70 forecasts from the GFS and European model ensembles showed 94L developing into a tropical depression by Monday. The coast of the southern Gulf of Mexico along the Bay of Campeche is ringed by high mountains that tend to deflect the flow of air into a counter-clockwise path, adding spin that helps aid formation of tropical cyclones. In their 8 am EDT Saturday Tropical Weather Outlook, NHC gave 94L 2-day and 5-day development odds of 40%. I put these odds higher, at 60%, given the appearance of 94L on satellite imagery on Saturday morning, and the propensity of the Bay of Campeche to help spin up tropical cyclones. If 94L becomes a tropical storm, it would be named Danielle. I don't see heavy rains from 94L reaching South Texas.

Jeff Masters

Hurricane

WU Storm App: Now on Android

By: Bob Henson , 7:53 PM GMT on June 17, 2016

Android users who’ve been hungering for access to WU’s Storm app, which debuted in 2015 on iOS devices, have cause to celebrate: Storm is now available for you! Android users can download Storm within the Google Play Store. For iOS users, it’s available within iTunes or the App Store.

Storm builds on the usefulness and clean design of the main WU app, and the data and forecasting strengths of WU and The Weather Company, to provide an array of features designed with storm trackers and weather enthusiasts in mind. The app allows you to view current conditions, daily or hourly forecasts at a glance and in a more detailed view, all drawing on WU’s network of more than 200,000 personal weather stations (PWSs). Storm also provides a wealth of other features specifically designed for keeping track of extreme weather.



High-definition radar: Storm provides access to data from the national network of NEXRAD radar sites at the top resolution available, with a razor-sharp 250 meters (800 feet) between data points. Users can view animations of past activity and extrapolations of current activity out to two hours ahead.

Storm tracks: For each key area of current storm action identified by the app, Storm provides a strength rating, storm motion, precipitation rate, any potential hazards (such as wind, hail, lightning, and tornadoes), and more.

Full-screen interactive map: The fully customizable Storm map interface allows you to display lightning, fronts, PWS data, and even earthquakes. I especially like the semi-transparent display of NWS watches, warnings, and advisories, which makes it easy to see where more than one type of alert is in effect.

Customizable alerts and notifications: Users can be notified of warnings and other alerts issued by NOAA, Environment Canada, and MeteoAlarm. Up-to-the-minute severe weather alerts are also available through widgets.

Socialize your weather: Storm allows you to share storm-tracking details and radar data with your friends and family via text message, email, Facebook, or Twitter.

Storm can be installed on Android phones and 7-inch tablets. The app can be used free of charge; for an ad-free experience, you can purchase a one-year subscription for $1.99. One user of Storm told us: "Storm is the best app out there. I've bought over 30 weather apps. Nothing (including several apps combined) comes close.”

Here comes the heat
A hot weekend is coming up for most of the nation, and the Southwest in particular. We’ll have a full update Monday on this weekend’s record-threatening Southwest heat wave, which may intensify northward into California and eastward into the central states next week. We are also keeping an eye on Invest 93E in the eastern North Pacific. This system is moving away from Mexico and into a less favorable environment, and NHC has reduced its chance of development to 40% over the next 5 days.

Have a great weekend, everyone, and stay cool!

Bob Henson


Figure 1. WU depiction of maximum temperature predicted at midday Friday for Saturday, June 18, 2016, by the National Digital Forecast Database.

Wunderground News

NOAA and NASA: Earth’s Warmest May on Record

By: Jeff Masters and Bob Henson , 7:23 PM GMT on June 16, 2016

The warming influence of the intense 2015 - 2016 El Niño event is waning, but May 2016 was still the planet's warmest May since record keeping began in 1880, said NOAA's National Centers for Environmental Information (NCEI) on Thursday. In the NOAA database, May 2016 came in 0.87°C (1.57°F) warmer than the 20th-century average for May, beating the previous record for May, set in 2015, by 0.02°C. This is the smallest margin the monthly global temperature has broken a record by since August 2015. NASA also reported the warmest May in its database, although the Japan Meteorological Agency placed May 2016 just a whisker (0.01°C) behind May 2015. May 2016 marked the 13th consecutive month that the global monthly temperature record was broken--the longest such streak since global temperature records began in 1880. Global ocean temperatures were the warmest on record for any May, but global land temperatures were the third warmest. Global satellite-measured temperatures in May 2016 for the lowest 8 km of the atmosphere were the 2nd warmest for any May in the 38-year record, and the year-to-date period was the warmest on record, according to the University of Alabama in Huntsville (UAH).

The impressive global warmth in recent months is due to the steady build-up of heat-trapping greenhouse gases due to human activities, plus a spike due to a large amount of heat being released from waters in the Eastern Pacific due to the powerful 2015-16 El Niño event. This event peaked in December, and NOAA’s global surface temperature for the year so far (January-May 2016) is a remarkable 0.24°C (0.43°F) warmer than the previous record, set in 2015 (see Figure 1). Last month, NASA/GISS director Gavin Schmidt laid 99% odds on this year becoming the warmest in global records, which would make it Earth's third consecutive warmest year on record.


Figure 1. Cumulative departures from normal in global temperature (year to date) for each month in 2016. For the year thus far (January-May), 2016 is head and shoulders above all other years in the NOAA database going back to 1895. The six closest competitors are shown above. Image credit: NOAA/NCEI.



Figure 2. Departure of temperature from average for May 2016, the warmest May for the globe since record keeping began in 1880. Areas with record warmth included much of Southeast Asia and parts of northern South America, Central America, the Caribbean, the Middle East, and northern and eastern Australia. Pockets of record warmth were observed across every major ocean basin, including the northwestern and southwestern Atlantic Ocean, much of the Indian Ocean, parts of the southwest Pacific Ocean and southern Pacific Ocean. Image credit: National Centers for Environmental Information (NCEI).


Figure 3. Departure from average for the global January-through-May temperature for the years 1880 - 2016. As is evident here and in Figure 1, this year has seen by far the warmest temperatures on record for the year-to-date period. Image credit: NOAA/National Centers for Environmental Information (NCEI).

El Niño is over
El Niño dissipated in May 2016, giving way to ENSO-neutral conditions as sea surface temperatures continued to decrease across the tropical Pacific Ocean. According to NOAA's >Climate Prediction Center, La Niña is favored to develop during late Northern Hemisphere summer 2016, with a nearly 75 percent chance for La Niña during the fall and winter 2016–17. See our post from June 9 for more on the anticipated big switch.

Arctic sea ice at its lowest May extent on record
May sea ice extent in 2016 was the lowest in the 38-year satellite record, according to the National Snow and Ice Data Center (NSIDC). The melt rate in the Arctic was 2 - 4 weeks ahead of the pace of 2012, which ended up with the lowest summer sea ice extent on record. However, the melt rate slowed dramatically in the first half of June, and it remains uncertain whether a record will be set. Snow cover in the Northern Hemisphere in May 2016 was the fourth lowest for May and was a record low for spring (March, April, and May), as reported from 50 years of mapping by the Rutgers University Global Snow Lab. Over the last several decades, Northern Hemisphere snow cover has changed little in autumn but has declined markedly in spring.

Four billion-dollar weather disasters in May 2016
According to the May 2016 Catastrophe Report from insurance broker Aon Benfield, four billion-dollar weather-related disasters hit the planet in May--a wildfire in Ft. McMurray, Canada, flooding from Tropical Cyclone Roanu in Sri Lanka, flooding in Northern Europe, and a drought in India. Between January - May 2016, there were sixteen billion-dollar weather disasters. This is well ahead of pace of thirteen such disasters in January - May 2013--the year that ended up with the most billion-dollar weather disasters on record: 41. Here is the tally of billion-dollar weather disasters for January - May 2016:

1) Drought, Vietnam, 1/1 - 6/1, $6.7 billion, 0 killed
2) Drought, India, 1/1 - 6/1, $5.0 billion, 0 killed
3) Flooding, Germany, France, Austria, Poland, 5/26 - 6/6, $5.0 billion, 17 killed
4) Severe Weather, Plains-Southeast U.S., 4/10 - 4/13, $3.75 billion, 1 killed
5) Wildfire, Fort McMurray, Canada, 5/1- 5/30, $3.1 billion, 0 killed
6) Winter Weather, Eastern U.S., 1/21 - 1/24, $2.0 billion, 58 killed
7) Winter Weather, East Asia, 1/20 - 1/26, $2.0 billion, 116 killed
8) Severe Weather, Rockies-Plains-Southeast-Midwest U.S., 3/22 - 3/25, $1.75 billion
9) Tropical Cyclone Roanu, Sri Lanka, India, Bangladesh, Myanmar, China, 5/14 - 5/21, $1.7 billion, 135 killed
10) Drought, Zimbabwe, 1/1 - 3/1, $1.6 billion, 0 killed
11) Flooding, Argentina and Uruguay, 4/4 - 4/10, $1.3 billion, 0 killed
12) Severe Weather, Plains-Midwest-Southeast-Northeast U.S., 3/4 - 3/12, $1.25 billion, 6 killed
13) Severe Weather, Plains-Midwest-Southeast-Northeast U.S., 2/22 - 2/25, $1.2 billion, 10 killed
14) Flooding, Plains-Rockies U.S., 4/15 - 4/19, $1.0 billion, 9 killed
15) Severe Weather, Plains-Southeast U.S., 3/17 - 3/18, $1.0 billion, 0 killed
16) Tropical Cyclone Winston, Fiji, 2/16 - 2/22, $1.0 billion, 44 killed

And here are the four disasters from May 2016:


Disaster 1.  Cyclone Roanu brought torrential rainfall and devastating floods and landslides to much of Sri Lanka and portions of India, Bangladesh, Myanmar, and China on May 14 - 21, 2016. At least 135 people were killed and damages were estimated at over $1.7 billion. In this image, we see Sri Lankan military personnel take part in relief and rescue efforts following a landslide in the village of Bulathkohupitiya on May 18, 2016. (STR/AFP/Getty Images)


Disaster 2. Canada's most expensive natural disaster in history came in May 2016, when a devastating wildfire roared through Fort McMurray, Alberta, causing at least $3.1 billion in damage. In this photo, we see a group trying to rescue animals from Fort McMurray waiting at a road block on Highway 63 as smoke rises from the fire on May 6, 2016. Image credit: Cole Burston/AFP/Getty Images.


Disaster 3. El Niño-related drought conditions that began in India in 2015 intensified during 2016, causing at least $5 billion in losses. The drought was worsened by a May heat wave that brought the hottest temperature ever recorded in India--51.0°C (123.8°F) at Phalodi on May 19, 2016. In this image, we see residents of New Delhi enduring another day of sizzling heat on Monday, May 2, 2016. Temperatures  hit a record 46°C (114.8°F) at Indira Gandhi International Airport and 44°C (111.2°F) at the city’s Safdarjung observatory that day. Image credit: Ramesh Sharma/India Today Group/Getty Images.


Disaster 4. Extratropical storm "Elvira" spawned numerous severe thunderstorms and torrential rains across parts of northern Europe between May 26 and June 6, killing at least 17 people and causing $5 billion in damage. The heaviest damage was in Germany, France, Austria, Poland and Belgium. In this image, we see firemen rescuing two women on June 3, 2016 in Simbach am Inn, Germany. (Photo by Sebastian Widmann/Getty Images)

Notable global heat and cold marks set for May 2016
Hottest temperature in the Northern Hemisphere: 52.2°C (126.0°F) at Larkana, Pakistan, 19 May
Coldest temperature in the Northern Hemisphere: -37.6°C (-35.7°F) at Geo Summit, Greenland, 5 May
Hottest temperature in the Southern Hemisphere: 40.3°C (104.5°F) at Derby Aerodrome, Australia, 3 May
Coldest temperature in the Southern Hemisphere: -78.1°C (-108.6°F) at Nico, Antarctica, 15 May
(Courtesy of Maximiliano Herrera.)

Major weather stations that set (not tied) new all-time heat or cold records in May 2016
A record heat wave in Southeast Asia led to an uncommonly long list of all-time local heat records in that region:
Oaxaca Airport (Mexico) max. 39.1°C, 1 May
Car Nicobar (India) max. 35.5°C, 2 May; increased to 36.5°C on 9 May
Truong Sa (Vietnam) max. 36.2°C, 3 May; increased to 36.9°C on 14 May
Jaffna (Sri Lanka) max. 37.1°C, 3 May
Mersing (Malaysia) max. 37.8°C, 4 May; increased to 38.2°C on 18 May
Phuket (Thailand) max. 37.9°C, 5 May
Iba (Philippines) max. 39.2°C, 5 May
Nakhon Sawan (Thailand) max. 43.5°C, 6 May; increased to 43.7°C on 7 May
Mae Sot (Thailand) max. 41.8°C, 7 May
Saravane (Laos) max. 42.0°C, 7 May
Dawei (Myanmar) max. 39.5°C, 7 May
Pachuca (Mexico) max. 32.5°C, 8 May
Kota Kinabalu (Malaysia) max. 36.5°C, 8 May
Toungoo (Myanmar) max. 43.0°C, 10 May; increased to 43.4°C on 11 May; increased to 44.0°C on 16 May
Mengla (China) max. 38.2°C, 10 May; increased to 38.4 on 11 May
Phitsanulok (Thailand) max. 42.7°C, 11 May
Surat Thani (Thailand) max. 41.4°C, 11 May
Houei Sai (Laos) max. 41.2°C, 11 May
Chiang Mai (Thailand) max. 42.5°C, 11 May
Chiang Rai (Thailand) max. 41.8°C, 12 May
Koh Sichang (Thailand) max. 38.0°C, 16 May
Mergui (Myanmar) max. 39.5°C, 18 May
Phalodi (India) max. 50.5°C; 18 May increased to 51.0°C on 19 May:  New national record high for India
Churu (India) max. 49.1°C, 18 May; increased to 50.2°C on 19 May
Kandla (India) max. 48.4°C, 18 May
Surendranagar (India) max. 47.8°C, 18 May
Amreli (India) max. 46.8°C, 19 May
Bikaner (India) max. 49.5°C, 19 May
Jodhpur (India) max. 48.8°C, 19 May
Pilani (India) max. 47.5°C, 19 May
Ahmedabad (India) max. 48.0°C, 19 May
Erinpura (India) max.  48.4°C, 19 May
Sawai Madhopur  (India) max. 48.7°C, 19 May
Jalore (India) max. 48.9°C, 19 May
Mount Abu (India) max. 39.4°C, 19 May
Bhopal (India) max. 46.7°C, 20 May

(Courtesy of Maximiliano Herrera.)

One all-time national heat record set in May 2016
One nation--India--set a record in May 2016 for its all-time hottest temperature on record. From January through June 16, 2016, a total of eleven nations or territories tied or set all-time records for their hottest temperature in recorded history--which is a very large number of records for so early in the year. One all-time cold temperature record has been set so far in 2016 (in Hong Kong.) "All-time" record here refers to the warmest or coldest temperature ever reliably reported in a nation or territory. The period of record varies from country to country and station to station, but it is typically a few decades to a century or more. Most nations do not maintain official databases of extreme temperature records, so the national temperature records reported here are in many cases not official. Our data source is international weather records researcher Maximiliano Herrera, one of the world's top climatologists, who maintains a comprehensive list of extreme temperature records for every nation in the world on his website. If you reproduce this list of extremes, please cite Maximiliano Herrera as the primary source of the weather records. Here are 2016's all-time heat and cold records as of June 16:

Niger set its all-time hottest record on June 8, 2016, when the mercury hit 49.0°C (120.2°F) at Bilma.

India set its all-time hottest record on May 19, 2016, when the mercury hit 51.0°C (123.8°F) at Phalodi.

Maldives set its all-time hottest record on April 30, 2016, when the mercury hit 35.0°C (94.8°F) at Hanimaadhoo.

Thailand set its all-time hottest record on April 28, 2016, when the mercury hit 44.6°C (112.3°F) at Mae Hong Son.

Cambodia set its all-time hottest record on April 15, 2016, when the mercury hit 42.6°C (108.7°F) at Preah Vihea.

Burkina Faso set its all-time hottest record on April 13, 2016, when the mercury hit 47.5°C (117.5°F) at Dori.

Laos set its all-time hottest record on April 12, 2016, when the mercury hit 42.3°C (108.1°F) at Seno.

Vanuatu in the South Pacific set its all-time hottest record on February 8, 2016, when the mercury hit 36.2°C (97.2°F) at Lamap Malekula.

Tonga set its all-time hottest record on February 1, 2016, when the mercury hit 35.5°C (95.9°F) at Niuafoou.

Wallis and Futuna Territory (France) set a new territorial heat record with 35.8°C (96.4°F) on January 10, 2016 at Futuna Airport. This is the second year in a row that Wallis and Futuna has beaten its all-time heat mark; the previous record was a 35.5°C (95.9°F) reading on January 19, 2015 at the Futuna Airport.

Botswana set its all-time hottest record on January 7, 2016, when the mercury hit 43.8°C (110.8°F) at Maun.

Hong Kong Territory (China) set its all-time coldest mark on January 24, 2016, when the mercury dipped to -6.0°C (21.2°F) at Tai Mo Shan.

Antarctica records its warmest minimum temperature on record
On May 27, 2016, the daily low temperature at Esperanza Base, on the outer end of the Antarctic Peninsula, was 8.8°C (47.8°F), which appears to be the warmest daily low on record anywhere in Antarctica, including the Antarctic Peninsula, King George Island, and other islands lying below the 60°S latitude that are considered part of the continent by the Antarctic Treaty. (WU weather historian Christopher Burt has a post on Antarctica’s all-time high of 17.5°C (63.5°F), set at Esperanza in March 2015.) Herrera has not found any other examples of daily lows in Antarctica any milder than 6.5°C. “For a continental record, this was smashed by an amazing margin,” he stated in an email. The high temperature at Esperanza the previous day--May 26, 2016--hit 17.2°C, which was its second highest temperature on record, just behind the famous 17.5°C record set last year. The late May 2016 records are truly remarkable since they were set less than a month before the onset of meteorological winter.

Africa records its warmest minimum temperature on record
On May 1, 2016, the highest minimum temperature ever recorded in Africa occurred, with a 37.5°C (99.5°F) reading at Yelimane, Mali. According to Herrera, only one minimum temperature in Africa was higher--a 38.0°C reading at Massawa, Eritrea on 30 June 1947. However, the values at that time were all rounded to 1°C, so this may not have been the actual minimum.

Jeff Masters and Bob Henson

Climate Summaries

U.S. Heat Builds: Parts of Southwest May Approach All-Time June Highs

By: Bob Henson , 5:18 PM GMT on June 15, 2016

Earth’s warmest year on record so far will make its presence felt in North America during the latter half of June. A massive dome of high pressure at upper levels will take shape across the United States this weekend and persist through next week. Subsidence beneath the high pressure will warm the atmosphere and help temperatures to soar well above average over large parts of the nation. The most immediate concern is across the Southern Plains and Mississippi Valley, where very moist low-level air combined with the building heat has led to heat advisories across many areas for Wednesday and/or Thursday. Residents of St. Louis, MO, may see their fifth consecutive day of heat index readings above 100°F by Thursday, and heat index values near or above 105°F are predicted on Wednesday and Thursday in Kansas City, MO; Tulsa, OK; Little Rock, AR; and Dallas-Fort Worth, TX. Only slight relief is expected toward the weekend. As an upper-level low traverses the north side of the ridge early next week, another burst of intense heat may develop ahead of it over the Northern Rockies and shift eastward across the Plains and Midwest.

Meanwhile, the deserts of southern California, Nevada, and Arizona--which largely missed out on the rains of El Niño--are now heating up quickly. Late June is typically the hottest time of the year in southeast New Mexico, southern New Mexico, and far west Texas (see Figure 3 below). It usually takes till July for the deserts of southwest AZ and southern CA to hit their peak of summer heat, so the upcoming heat wave is an early one there. An excessive heat watch is already in effect across parts of the far Southwest, where temperatures are expected to peak above the century mark on Sunday and/or Monday in such cities as Tucson, Phoenix, Las Vegas, and Los Angeles. Figure 2 shows the latest WU forecasts compared with record highs for June and for any month. Phoenix’s hottest high on record prior to the first day of summer is 115°F, so Sunday is likely to break that mark. In Los Angeles, record heat this time of year depends hugely on local effects, such as the presence or absence of offshore winds, as well as the large-scale factors that will be present this weekend.



Figure 1. National Weather Service alerts on Wednesday morning, June 15, 2016, included a heat advisory for parts of the south-central US (orange) and an excessive heat watch for parts of the Desert Southwest (dark red). Image credit: NOAA/NWS.


Figure 2. WU temperatures for several major southwestern U.S. cities issued on Wednesday morning for Sunday and Monday, June 19-20, 2016, compared with record readings for June and for any time of the year. *Note: NWS records (NOWData) show 117°F at Tucson International Airport on June 26, 1990, as the highest official temperature for the Tucson area, going back to September 1894. An even higher reading of 118°F at the Tucson Magnetic Observatory was recorded on June 27, 1990, according to weather records researcher Maximiliano Herrera. However, based on his knowledge of the instrumentation in use in 1990 (an aspirator later found to be problematic), Herrera believes that both of these temperatures are most likely slight overestimates, and that the most reliable all-time records for Tucson are the 115°F readings at the Tucson NWS office on June 19, 1960; June 26, 1990; and July 28, 1995.


How does the National Weather Service classify dangerous heat?
Every NWS office except those in Alaska has its own set of criteria for issuing heat watches and warnings, based on local climatology. An excessive heat warning is used in the most dangerous situations, when vulnerable people can experience serious health effects. The national standard (which can be adjusted by local offices) is to issue an excessive heat warning when the heat index is expected to be at least 115°F for at least three hours, and/or at least 105°F for three days. A heat advisory is issued at a lower threshold, typically for a heat index of 105°F together with nighttime lows at or above 80°F. The thresholds for a heat advisory may be even lower for multiday heat waves (due to the cumulative effect of intense heat) or for events striking early in the season (see Figure 3 below). An excessive heat watch generally indicates that the excessive heat warning criteria may be met within the next 24 to 48 hours, again varying by location. For example, because the Los Angeles and San Diego NWS offices employ differing thresholds, the excessive heat watch for this weekend does not include Los Angeles County, even though temperatures will be comparable on either side of the county’s eastern border.


Figure 3. Average date of peak summertime temperature varies from late June near El Paso, TX, to late August along parts of the TX and LA Gulf Coast. Sunlight is most intense near the summer solstice (usually June 20 or 21), which heats up dry areas quickly, but the peak summer heat often takes a few weeks to build in relatively moist areas, especially the south-central states. Image credit: NOAA/NWS. For more on this topic, see the related post by Christopher Burt, “Warmest Days of the Year for the U.S.”.


The challenge of air travel in fierce Desert Southwest heat
The upcoming scorcher could give the great heat wave of June 1990 a run for its money in some areas. On June 26, 1990, Los Angeles notched an all-time June record of 112°F, while Tucson and Phoenix set all-time highs for any date with almost-unfathomable readings of 117°F and 122°F, respectively. Temperatures in this range can actually impede air travel, since the near-ground atmosphere becomes so thin that some types of aircraft cannot obtain sufficient lift to take off. Extreme heat can also damage the internal components of some aircraft. Phoenix’s Sky Harbor Airport halted all takeoffs as a precaution during the all-time record heat of June 1990. Urban legend has it that the closure was due to the tarmac melting, but an airport spokesperson confirmed to KJZZ radio last year that it was uncertainty about aircraft performance at that temperature that actually led to the closure. More recently, on June 29, 2013, 18 US Airways flights were cancelled because the regional aircraft involved had been certified for takeoff in temperatures of no more than 118°F, according to the UK Telegraph. Temperatures on that day hit 119°F in Phoenix, the city’s third-highest reading on record.

Hot times at high latitudes
Global temperatures continue to run at a near-record pace as we transition from the recently deceased El Niño toward a potential La Niña. We’ll have a full report on May’s global climate with the release of NOAA’s monthly summary later this week, including another bumper crop of all-time local heat records. Two of the most striking heat reports in the last several weeks have come from opposite ends of the globe.

On May 27, the daily low temperature at Esperanza Base, on the outer end of the Antarctic Peninsula, was 8.8°C (47.8°F). According to weather records researcher Maximiliano Herrera, this appears to be the warmest daily low on record anywhere in Antarctica, including the Antarctic Peninsula, King George Island, and other islands lying below the 60°S latitude that are considered part of the continent by the Antarctic Treaty. (WU weather historian Christopher Burt has a post on the all-time high of 17.5°C (63.5°F), set at Esperanza in March 2015.) Herrera, who maintains a comprehensive list of extreme temperature records for every nation in the world on his website, has not found any other examples of daily lows in Antarctica any milder than 6.5°C. “For a continental record, this was smashed by an amazing margin,” he added.


Figure 4. The extent of melting on the surface of the Greenland Ice Sheet hit dramatic seasonal peaks in April, May, and early June 2016, most recently approaching the 40% mark. Image credit: NSIDC.


Only a few days after the mild night at Esperanza, a major burst of early-season warmth swept across southwest Greenland. According to the Dutch meteorological agency DMI, temperatures at the Nuuk airport hit 24.8°C (76.6°F) on Friday, June 9. This is the warmest reading ever observed in Greenland for the month of June, easily topping the 23.3°C (73.9°F) set on June 15, 2014, in Kangerlussuaq, about 200 miles north of Nuuk. Downslope winds blowing offshore from the mountains of southwest Greenland helped warm the atmosphere in the Nuuk area (the same process that drives foehn and chinook warming). Nuuk’s record high resulted from this downslope warming on top of already-unusual mildness throughout the depth of the atmosphere over much of Greenland. This extreme early-June warmth led to the third noteworthy spike of the year in surface melting atop Greenland’s ice sheet, following major melt events in April and May (see Figure 4 above).

Still waiting on our first Eastern Pacific tropical storm
The tropics remain fairly quiet, with the only system currently being tracked--Invest 93E in the eastern North Pacific--expected to organize only slowly over the next few days as it moves away from the Mexican coastline. In its 8:00 AM EDT tropical weather outlook, the National Hurricane Center gives 93E a 20% chance of development by Friday and a 50% chance by Monday. If it does become a tropical storm, it will be Agatha, the first named storm of the Eastern Pacific season. Meanwhile, a surface low associated with an upper-level impulse moving toward the East Coast may undergo some organization this weekend well off the East Coast, although models have largely backed off on potential tropical/subtropical development as surface high pressure is projected to dominate the Northwest Atlantic.

We'll be back with a new post on Thursday.

Bob Henson


Figure 5. Infrared satellite image showing an area of disturbed weather off the southern coast of Mexico (Invest 93) as of 1500Z (11:00 AM EDT) Wednesday, June 15, 2016. Image credit: NASA/MSFC Earth Science Office.

Extreme Weather Heat

Spring Heads to a Toasty Finish across the U.S.

By: Bob Henson , 4:39 PM GMT on June 13, 2016

The final week of northern spring will have a summery feel across the heart of North America, including much of the U.S. Rockies, Plains, Midwest, and Deep South. In most places, the heat won’t be smashing daily records, but it may persist or recur into next week, adding to its cumulative impact on people and ecosystems. Temperatures are likely to top 100°F from western TX to western KS later this week, with readings from 95°F to 100°F widespread from Arkansas and Louisiana across the South to Georgia by Thursday/Friday. Ample Gulf moisture will push heat indexes well into dangerous territory across large parts of the nation’s midsection and into the Southeast later this week (see Figure 1).


Figure 1. Maximum heat index values are projected to exceed 105°F on Thursday, June 16, 2016, over a large area from the Missouri and Arkansas Valleys of OK, KS, and NE across the mid-Mississippi Valley and parts of the Deep South to the lower elevations of North and South Carolina.. This outlook takes model ensemble data and statistical temperature forecasts into account. There is a chance of heat-index values exceeding 115 on Thursday over parts of the Missouri and Mississippi Valleys. The NWS calculates heat index values by incorporating the effects of both temperature and relative humidity on bodily comfort. Values above 105°F are considered dangerous during periods of prolonged exposure and/or strenuous activity. Image credit: NOAA/NWS/WPC.


Figure 2. An extremely strong upper-level high will will bring very hot temperatures this coming weekend across the Southwest U.S. Shown here are high and low centers averaged across the 22 members of the GFS Ensemble Forecast System (GEFS), for runs produced at 06Z Monday, June 13, 2016, and valid at 18Z (2:00 PM EDT) Sunday, June 19. The labeled lines show the height of the 500-millibar pressure level, expressed in decameters (tens of meters). The higher the pressure level, the warmer the air below it. Values greater than 600 dm, as shown here for the Four Corners area, are only observed during the most extreme heat waves; it’s impressive to see such values showing up in an ensemble average. The orange and blue colors show how much the pressure levels at a given location are above or below the seasonal average, again in decameters. Image credit: www.tropicaltidbits.com; thanks to Richard Grumm, NWS/State College, for calling attention to this model result.


Southwest deserts will be scorching by the weekend
Some of the worst heat in many years could take shape this coming weekend in cities like Phoenix, Yuma, and Tucson, Arizona. Already this month, Phoenix has seen four consecutive record highs (6/3 through 6/7), including the earliest 115°F reading (6/4) since record-keeping began there in 1895. The coming week should bring only garden-variety heat to southern Arizona, which means daily highs within a few degrees of the century mark Fahrenheit, but high pressure building aloft will sharpen the heat dramatically by week’s end. As of Monday morning, the WU forecast for next Sunday, June 19, is calling for highs of 117°F in Phoenix, 116°F in Yuma, and 113°F in Tucson. If it verified, the Phoenix reading would be the warmest on record on any date prior to the summer solstice, and these temperatures are not too far from the all-time records of 122°F in Phoenix (June 26, 1990), 124°F in Yuma (July 28, 1995), and 117°F in Tucson (June 26, 1990). An excessive heat watch is already in effect for much of southwest Arizona and far southeast California, including the Phoenix area, for this coming Friday morning through Monday evening.

Record highs are far outpacing record lows so far this year
Last week’s national climate roundup for May showed that 2016 for the period January through May was running fourth hottest in U.S. history behind only 2012, 2000, and 2006. Statistics from NOAA on daily record highs and lows back up this picture of a very warm year in the U.S. so far. The period from January through May 2016 saw 11,065 daily record highs and only 1,820 record lows (either tied or broken), according to the Daily Weather Records site maintained by NOAA/NCEI. This ratio of around 6 to 1 is very high for a five-month-long period. The lopsided ratio has continued into June: the first nine days of the month produced a preliminary total of 850 daily record highs and 44 daily record lows, according to NOAA/NCEI.

The oddly cool years of 2013 and 2014 both ended up with more daily record lows than record highs, but otherwise there’s been enough heat in this decade to produce a total of 194,467 record highs and 96,651 record lows, according to independent meteorologist Guy Walton, who has tracked daily record highs and lows for many years using NOAA/NCEI data. As shown in Figure 3, the ratio since 2010 of just over 2 record highs to each record low is now outpacing the ratio of just under 2:1 for the previous decade (2000-2009).


Figure 3. The ratio of daily record highs to daily record lows across the United States for each decade since the 1920s, expressed as an increment beyond the 1:1 ratio that one would expect in a stationary climate (one not being warmed by added greenhouse gases). The 2000s produced nearly twice as many record highs as record lows, and thus far the 2010s have been even more heat-skewed. Image credit: Guy Walton.


A journey from severe weather in the Plains to low pressure off the East Coast
A shot of upper-level energy now located over the Desert Southwest is destined to take an interesting path over the next week. As the impulse encounters very warm, unstable air across the Plains, NOAA’s Storm Prediction Center is calling for an enhanced risk of severe weather on Monday across parts of the central High Plains on Monday, shifting to the Missouri and Mississippi Valley on Tuesday. The first half of June is peak tornado season in eastern Colorado, and the Monday setup favors potentially tornadic supercells. Later on Monday night, a large thunderstorm complex packing high wind may rumble eastward across the Central Plains, with a similar complex possible Tuesday night further east. The upper-level impulse and associated severe weather should track onward into the Ohio Valley on Wednesday.


Figure 4. WU depictions of severe weather risk areas for Monday and Tuesday, June 13-14, 2016, as issued by NOAA’s Storm Prediction Center on Monday morning. Areas of enhanced risk (the third highest of five SPC threat levels) were in place for both days.


Toward Friday and the weekend, the upper-level energy will dive south, feeding into the base of a large North Atlantic upper low. This tail-end circulation may be enough to generate a surface low somewhere off the mid-Atlantic or Southeast coast. Several weekend runs of the GFS and ECMWF models suggested that the eventual surface low could linger for a day or two near the Gulf Stream with a piece of the tail-end upper circulation parked over it. Sunday night’s 06Z GFS run backed away from this scenario, moving the upper-level and surface lows eastward more quickly, while the 12Z Monday GFS brings a surface low into the Southeast coast early next week. This setup is worth monitoring for the potential of at least weak subtropical development, keeping in mind the large amount of model uncertainty and long time frame.

It was a quiet weekend across the globe’s tropics, with no systems being tracked by operational agencies on Monday morning. In the eastern North Pacific, we could see a center of low pressure emerge from a large, persistent area of disturbed weather south of the Gulf of Tehuantepec. In their outlook issued at 8:00 AM PDT Monday, the NOAA National Hurricane Center gave this area 10% odds of tropical development by Wednesday morning and 50% odds by Saturday morning, with the center of action drifting west-northwest and remaining off the Mexican coast.

We’ll be back with a new post by Wednesday at the latest.

Bob Henson

Heat Extreme Weather

Climate Signals and “Demystifying Climate Models”: Two Great New Resources

By: Jeff Masters and Bob Henson , 4:11 PM GMT on June 10, 2016

Whether it be in media coverage or in statements by politicians, the connections between our warming planet and extreme weather events are too often ignored or downplayed (or sometimes overplayed). Those who want to learn more about the global climate models that bolster our understanding of past, recent, and future change can face a seemingly impenetrable wall of jargon, formulas, and technical terms. Where can you quickly find the context to put a breaking weather event into a solid climate perspective, or to get a handle on how global climate models work? Two excellent resources are now available to meet both of these needs.

A new tool for connecting the dots between extreme events and climate change
Debuting in beta form last month, the Climate Signals website--created by the nonprofit organization Climate Nexus--offers a quick and handy way to explore the climate change elements that are most pertinent to a given extreme event. The site’s main page allows you to click on a U.S. map that shows ongoing, recent, and significant past events, including heat waves, floods, and other weather disasters as well as ecosystem shocks such as wildfire and high-latitude ice loss. Click on an event and you get a brief summary, together with a curated list of media reports and relevant research findings. Each event also features a schematic “tree” that shows the chain of physical and social processes running from greenhouse gases to the event. Some of the trees are richly branched; others have as little as a single connection. Rather than showing the relative strength of the various factors compared to each other, or to natural variability, the trees are intended simply to show which aspects of climate change are most relevant to a given event. There is a “dashed line” branch used for links that are not yet firmly supported by observations but are consistent with model projections.


Figure 1. The schematic “tree” used to show connections between increased greenhouse gas emissions from human activity (left) and the torrential rains and severe flooding that struck northern Louisiana and nearby areas in early March 2016. More than 20 inches of rain fell in a four-day period in some areas. The dashed line indicates a link that is found in modeling but not yet fully supported by observations. The site notes: “This diagram does not quantify the relative strength of each factor, nor does it illustrate the natural factors that often shape extreme events, including natural variability and regular circulation changes.” Image credit: Climate Signals.


For journalists, policy makers, or any other interested parties delving into such high-profile events as Hurricane Sandy or the multi-year California drought, Climate Signals will serve as a convenient and easy-to-navigate starting point. Peer-reviewed attribution studies--which are referenced throughout the Climate Signals site--are the place to dig deeper when researching how much a given facet of climate change may have influenced a particular extreme event. We also found that the Real Time Data page--which contains over 50 links to various websites on current extreme temperatures, rainfall, storms, drought, fire, sea level, insect activity, snow, and ice--is a fantastic resource for researching the real-time impacts of extreme weather. The Climate Signals team is now seeking feedback on its beta site. 



Ricky Rood has a book out!
As those of you who follow wunderground climate change blogger Dr. Ricky Rood know, Ricky has bravely forayed into the world of long-form publication with his first-ever book: Demystifying Climate Models: A Users Guide to Earth System Models. A free electronic version is available as well. First author Dr. Andrew Gettelman (a climate scientist and expert on aerosols and cloud microphysics who is based at NCAR, the National Center for Atmospheric Research) and Ricky have written a book aimed at scientists and engineers in fields such as ecosystems, water resources, and urban planning who need quantitative climate change information for decision-making. By understanding climate models and their uncertainties, the reader should become a more competent interpreter or translator of climate model output. Although the book delves into many aspects of how climate models work, it is not a technical manual: there are virtually no equations, and the writing is conversational and accessible.

The book is full of enlightening examples of the strengths and weaknesses of climate models. Here's one example from the chapter titled “Results of Current Models” that we found valuable: "There is no explicit law for how much precipitation will increase, but most model simulations indicate that the increase is about 2% per degree centigrade of warming. Precipitation is a classic case where some aspects of the impacts of climate change are well known, and some are much more uncertain. As noted briefly in Chap. 10, as the spatial scale of interest decreases, the large-scale constraints fall away, and potential model structural errors start to become larger. While models agree on the sign and even some of the magnitude of global trends, they do not agree on the magnitude (even the magnitude of global changes), and particularly on what happens in different regions."

Demystifying Climate Models does a tremendous job of filling the gap between highly technical textbooks and more superficial descriptions of climate modeling. Even better, anyone can download a PDF or ePub version at no cost via the book’s website. A hardcover print version is also available at a $59.99 list price, which is quite reasonable for a book of this quality and depth. The book’s production was partially supported by NCAR.

Quiet time in the tropics; a hot weekend ahead for the States
There are no tropical cyclones being tracked anywhere on Earth this morning, but there is plenty of heat around, with some impressive records being set in some far-flung locations. A new record in Greenland for the month of June was set on Thursday when the airport at Nuuk (Mittarfik Nuuk) soared to 24.7°C. Much of the central and eastern United States will be cooking this weekend, with temperatures soaring well above 90°F as far north as Minnesota and the Dakotas. We'll take a closer look at national and global heat next week. In the meantime, have a great weekend, and stay cool, everyone!

Jeff Masters and Bob Henson

Climate Change Computer Modeling

El Niño is Officially Over—and La Niña is Likely On the Way

By: Bob Henson , 5:27 PM GMT on June 09, 2016

The El Niño event of 2015-16 is now history, according to NOAA’s Climate Prediction Center (CPC), which certified the demise in an advisory on Thursday. It wasn’t exactly a tough call: the warm equatorial waters over the eastern tropical Pacific that have signaled El Niño’s presence for more than a year are pretty much gone. El Niño events are defined mainly by sea surface temperatures (SSTs) that are at least 0.5°C above average across the benchmark Niño3.4 region, which straddles the central and eastern equatorial Pacific. CPC also considers whether the atmosphere and ocean are acting in sync to support El Niño conditions (for example, trade winds over the tropical Pacific typically weaken as El Niño sets in). In the months since El Niño reached its peak intensity in November 2015, sea surface temperatures (SSTs) have steadily dropped across the Niño3.4 region, and other measures of El Niño strength have waned as well. Last week’s Niño3.4 SST anomaly (departure from average) dipped to -0.2°C, its lowest value since mid-March 2014. Below the surface of the tropical equatorial Pacific, cool anomalies now predominate, in part because of a strong upwelling oceanic Kelvin wave--an eastward-moving impulse that’s brought cooler water toward the surface along its path. Just as a downwelling Kelvin wave can help stimulate El Niño’s formation, upwelling Kelvin waves often feed into the development of La Niña, as one seems to be doing right now.


Figure 1. Anomalies (departure from average) in ocean temperature (degrees C) below the equatorial Pacific. The widespread blue values are consistent with the demise of El Niño and the expected development of La Niña. Image credit: NOAA/NWS/CPC.


Figure 2. Weekly anomalies (departure from average) in sea surface temperature (SST, in degrees C) across the “Niño regions” of the eastern and central tropical Pacific (see map at top of image). SSTs in the Niño3.4 region (third panel up from bottom) are at least 0.5°C above average during El Niño and at least 0.5°C below average during La Niña. NOAA employs a separate SST analysis across overlapping three-month intervals when assessing the total duration of an El Niño event. Image credit: NOAA/NWS/CPC.


An El Niño event becomes official for the record books once El Niño conditions have been in place for at least five overlapping three-month periods. By this definition, the most recent El Niño began in February-April-May 2015 and will most likely end in April-May-June 2016. Many El Niño events last just one year. This one would have been a rare two-year episode, extending back to late autumn 2014, were it not for a single three-month period (Jan-Mar 2015) that fell just below the El Niño threshold in the ocean dataset that NOAA uses (ERSSTv4).

A global footprint
Like the previous “super” El Niño events of 1982-83 and 1997-98‚ which are the only comparably strong events in the last 66 years of NOAA records, El Niño 2015-16 was a high-impact phenomenon. Among the repercussions linked to it:

--Devastating drought, fire, and air pollution in Indonesia and neighboring countries in fall 2015, which caused many thousands of people to fall ill and cost Indonesia more than $16 billion

--The wettest month on record across Texas and Oklahoma (May 2015), with subsequent rounds of torrential rain and major flooding over parts of the south-central U.S. in late 2015 and early 2016

--South Africa’s most expensive natural disaster on record, a severe drought culminating in the summer of 2015-16 that hammered crops and water supplies

--An intense heat wave in spring 2016 across Southeast Asia, with more than half of the major weather stations in Thailand setting all-time record highs

--Record-warm upper-ocean temperatures that produced the third global coral bleaching event on record and caused massive damage to the Great Barrier Reef, where more than 20% of the entire reef’s coral may have been killed.


Figure 3. Left: Coral researcher Kim Cobb (@coralsncaves, Georgia Institute of Technology) placing a conductivity-temperature-depth sensor on a healthy reef at Kirimati Island in the Southwest Pacific several years ago. Right: The same reef as of late April 2016, showing a large number of dead and dying coral colonies as a result of prolonged above-average water temperatures. Learn more about Cobb’s research and the devastation to coral reefs this year at this ENSO Blog entry (May 27, 2016). Image credits: Pamela Grothe (left), Kim Cobb (right).


One place where El Niño failed to behave as expected was Southern California, where forecasts and historical analogs suggested that heavier-than-usual rains were quite likely after four years of punishing drought. Instead, the West Coast rains were shunted hundreds of miles north of where they usually materialize during strong El Niño events. Seattle ended up with its wettest winter on record--a stupendous 45.51” of rain from October 1 through June 7--while Los Angeles saw only 6.88”, just 47% of its long-term average for that same period. Although the absence of El Niño rains was a big blow to Southern California, the unusual outcome together with ample data collected by a rapid-response NOAA field project in the Pacific may help spur some fascinating and important research.


Figure 4. Percent of average precipitation for the period from October 1, 2015, through June 7, 2016, based on provisional data. Most of the rainfall in a West Coast water year (October 1 - September 30) has fallen by June. Image credit: Western Regional Climate Center.

La Niña into 2018? It’s quite possible
There is high confidence (though not ironclad certainty) that El Niño will be quickly replaced later this year by La Niña. Even though the interplay between ocean and atmosphere that leads to El Niño is not fully understood, the mechanics of its downfall are more clear-cut, as explained nicely in a NOAA blog post last January. In a nutshell, El Niño’s inclination to push both wind and water eastward across the tropical Pacific can trigger oceanic Rossby waves. These huge, shallow, slow-moving impulses on either side of the equator can move west, bounce off the west end of the Pacific basin, and return to stimulate a cooling of the central and eastern tropical Pacific, often putting an end to El Niño and sometimes ushering in La Niña. (This process is in addition to the oceanic Kelvin waves noted above, with various types of interrelationships adding to the complexity.) On top of conceptual understanding, we know from past experience that most strong El Niño events tend to be followed rather promptly by at least a year of La Niña conditions. Moreover, seasonal climate models that include oceanic conditions agree strongly on the development of La Niña later this year. With all this in mind, the June outlook from forecasters at NOAA and the International Research Center for Climate and Society (IRI), released on Thursday, gives La Niña a 70-75% chance of being in place by late summer and continuing into at least early 2017.


Figure 5. The early-June outlook issued by forecasters at the NOAA/NWS Climate Prediction Center and the International Research Center for Climate and Society. Image credit: IRI/CPC.


Because many La Niña events last two or three years, there is already a slightly enhanced probability of La Niña in 2017-18, if history is any guide. A 2014 modeling study by Pedro DiNezio (@txgaucho, now at the University of Texas) and Clara Deser (National Center for Atmospheric Research) used a highly sophisticated global climate model (CCSM4) to analyze 252 La Niña events that appeared in 1300 years of simulated climate. The study found that about a third of the first-year La Niña events returned or persisted for a second year, but with marked variations from century to century. The historical record shows that second-year La Niñas have been even more frequent in the last 150 years than in the 1300-year simulation. WU member Eric Webb (@webberweather, North Carolina State University) has examined El Niño and La Niña events going back to 1865 using a blend of multiple datasets from several agencies. From the 23 “first-year” La Niña events in Webb’s database (focusing on the core winter period of December through February, or DJF), 11 of those events featured at least one more subsequent year of La Niña. Similarly, in the official NOAA database going back to 1950, exactly half of the 12 first-year La Niña winters were followed by a second year of La Niña. (NOAA’s Emily Becker digs further into the post-1950 statistics in a recent blog post.)

Considering this climatology, if we assume that La Niña materializes in 2016-17 as expected, the historical odds are about even that 2017-18 would also be a La Niña winter (potentially with a short neutral break in between). I wouldn’t bet the farm on this outcome, though--especially since the 75% odds of getting a La Niña this coming autumn, while quite high, are not a guarantee! “Some folks are pointing out that the subsurface cooling is not very strong relative to some past events,” says Michelle L’Heureux (NOAA/CPC), “so we still have to see if it is enough (and that the atmosphere couples to it, because right now there is no such coupling).” The next step toward making an actual La Niña forecast for 2017-18 would be to get past the early-2017 “spring predictability barrier”, when ongoing El Niño and La Niña events tend to weaken and climate model guidance become less robust.

What shoaling can tell us
Here’s one promising research angle that may help: The DiNezio-Deser study cited above found that the depth of the thermocline (the oceanic boundary that separates warmer surface waters from cooler subsurface waters) six months before the onset of La Niña was correlated with SSTs a year and a half later. When the thermocline shoals more strongly (becomes shallower) after El Niño, then there is a greater chance of a subsequent multi-year La Niña. According to DiNezio and Deser, this process could provide an 18-month lead time for predicting whether La Niña conditions might return a second year. In general, the thermocline shoals much more strongly after a strong El Niño event, which raises the odds that the subsequent La Niña will last more than a year. After the “super” El Niño of 1997-98, the thermocline rose by more than 40 meters (130 feet), and the subsequent La Niña lasted for three years. The El Niño of 2015-16 was just as strong as in 1997-98, but as of late May 2016, the thermocline had shoaled by no more than 20 meters (65 feet). “This makes the prediction of the return of La Nina for an additional year more challenging,” said DiNezio in an email. “The duration of the upcoming La Nina is not set in stone and will be difficult to predict. I like this event because it makes the prediction so much more challenging!”

Bob Henson

El Niño La Niña

A Moderate, Moist May across the Contiguous U.S.

By: Bob Henson , 4:07 PM GMT on June 08, 2016

Like a nation pulled out of the fridge and briefly popped into a toaster oven, the contiguous United States was relatively cool on the inside and quite warm on the margins last month, according to the monthly U.S. climate roundup released on Wednesday by NOAA’s National Centers for Environmental Information (NCEI). For the 48 states as a whole, it was a fairly moderate May, ranking as the 62nd coolest and 45th wettest in the past 122 years of recordkeeping. Temperatures reflected the influence of the fast-receding 2015-16 El Niño event, with relative coolness from the south central states into the mid-South and unusual warmth across the northern tier of states as well as California and Florida. None of the contiguous states had a top-ten coolest or warmest May, although Washington had its 11th warmest.


Figure 1. Statewide rankings for average temperature during May 2016, as compared to each May since 1895. Darker shades of orange indicate higher rankings for warmth, with 1 denoting the coldest month on record and 122 the warmest. Image credit: NOAA/NCEI.

A stunted temperature range for the Upper South and Mid-Atlantic
The month gets more interesting temperature-wise when you dig into the statewide average high and lows, where the general moistness of the atmosphere really plays out. Virginia is a striking example: the state’s average low temperature was the 38th mildest on record, but the average high temperature placed 7th coolest! The outcome was similar, if less dramatic, in neighboring states from South Carolina to Pennsylvania and New Jersey, all of which had cooler-than-average highs and warmer-than-average lows (see Figure 2 below).

It’s not surprising that Virginia led the pack in this tamped-down temperature range when you consider that the state had its 5th wettest May on record, as did Delaware (see Figure 3 below). Thick, low clouds are a surefire way to keep nights milder and days cooler, as they block sunlight by day and trap outgoing radiation from Earth at night that would otherwise cool the surface. The sogginess was reflected in Washington, D.C., with a stretch from April 27 to May 23 in which rain fell on 23 out of 27 days, the capstone to what Capital Weather Gang's Jason Samenow called "a truly lackluster spring." Many other U.S. states were wetter than average in May. The most noteworthy dry pocket was in Alabama and Mississippi, with relative dryness also prevailing from the Upper Midwest to New England.


Figure 2. Statewide rankings for average maximum temperature (left) and minimum temperature (right) during May 2016, with rankings depicted as in Figure 1 above. Image credit: NOAA/NCEI.


Figure 3. Statewide rankings for average precipitation during May 2016, as compared to each May since 1895. Darker shades of green indicate higher rankings for moisture, with 1 denoting the driest month on record and 122 the wettest. Image credit: NOAA/NCEI.


Figure 4. Average temperatures and long-term rankings for May 2016 in various communities across Alaska. Image credit: NWS/Alaska.

Alaska continues baking
After its warmest April on record, Alaska ended up with its second-warmest May, behind only the exceptional warmth of May 2015. At least five Alaskan communities had record monthly warmth in both April and May: Bethel, King Salmon, Kotzebue, St. Paul, and Talkeetna.

Still on track for a very warm U.S. year
Boosted by the influence of El Niño atop sharply rising global temperatures, the contiguous U.S. remains on track for what could be one of the warmest years in U.S. weather history. The January-to-May period came in fourth behind 2012, 2000, and 2006, with a departure from the long-term Jan-to-May average of an impressive 3.21°F. Some noteworthy June heat has already played out in the far West: Phoenix hit 115°F on Saturday, its earliest such reading on record. The heat will be building across much of the central and eastern U.S. as we head toward the first day of summer (which will be June 20 this year, but June 21 during the rest of the 2010s).

On the global scale, there’s an extremely good chance that 2016 will beat out 2015 as the warmest year on record. We’ll see where that distressing competition stands next week when NOAA releases its monthly global climate report on Friday, June 17, after similar reports from NASA and other temperature-tracking agencies.

I'll be back with a new post by midday Thursday.

Bob Henson

Climate Summaries

TS Colin Becomes Post-Tropical Near the North Carolina Coast

By: Bob Henson , 4:06 PM GMT on June 07, 2016

Looking more like a mammoth squall line than a tropical cyclone, former Tropical Storm Colin was reclassified as a post-tropical cyclone at 11 AM EDT Tuesday by the National Hurricane Center (NHC). The ill-defined center of Colin was placed at 34.0°N, 77.0°W, or about 40 miles east-southeast of Wilmington and 40 miles south-southwest of Morehead City. Colin was racing northeastward at 36 mph, a track that will take it well east of North Carolina by Tuesday afternoon. A tropical storm warning remained in effect from Cape Lookout to Oregon Inlet, NC, but will likely be discontinued early Tuesday afternoon. Nearly all of the intense showers and thunderstorms (convection) associated with Colin at midday Tuesday were located along an elongated zone extending from just east of Colin’s center hundreds of miles toward the south. With Colin’s west side so weak, rainfall has been less widespread and intense than earlier expected along the coastline from Georgia to North Carolina.


Figure 1. Infrared satellite image of Tropical Storm Colin at 1415Z (10:15 AM EDT) Tuesday, June 7, 2016. Image credit: NOAA/NESDIS.


Figure 2. A driver's automobile stalls during high tide of Tropical Storm Colin in the Westshore area of Tampa, Fla., Monday, June 6, 2016. Image credit: Octavio Jones/The Tampa Bay Times via AP.

Colin’s impact in Florida
Severe weather associated with Colin’s arrival in Florida was minimal, according to reports compiled by NOAA’s Storm Prediction Center as of Tuesday morning. There were only a handful of reports of high wind and just two tornadoes (one in Duval County in far northeast Florida, and the other a waterspout moving onto the southwest coast near Bonita Beach). Minor coastal flooding was widespread across Florida’s Gulf Coast as winds on the east side of Colin pushed water ashore. A storm surge of just over 4.3 feet was observed at Cedar Key, FL, during low tide around 9 PM EDT Monday. A few hours earlier, the surge was lower, but it combined with one of the largest high tides of the month (as a result of last weekend’s new moon) to create a total storm tide [storm effect + tidal effect] of 5.17 feet. This produced the highest water since 2006’s Tropical Storm Alberto in the low-lying Cedar Key region, flooding a number of businesses and topping the storm tide produced by Tropical Storm Debby in 2012. The juxtaposition of peak storm surge with monthly high tide cycles is both a curse and a blessing, according to storm surge expert Hal Needham: “When surge hits near full or new moon, the peak water level is a bit higher, but the event may be of a shorter duration, as water quickly recedes soon after the high tide.” Colin's water level at high tide came in about 5 inches above Needham’s prediction of 4.72 feet featured in our Monday morning blog post.


Figure 3. Preliminary data show that a storm surge of around 3 feet (red curve minus blue curve) coincided with high tide (blue curve) on Monday afternoon, June 6, 2016, at Cedar Key, FL. The storm surge was even larger during the subsequent low tide. Image credit: NOAA.

Tampa Bay gets a parting blow from Colin
Colin was much less organized than 2012’s Tropical Storm Debby, also a June storm from the eastern Gulf of Mexico. Debby produced a large area of rainfall topping 10” across northern Florida. Even though Colin’s sustained winds at landfall were higher than Debby’s, its rapid northeast motion and marked asymmetry kept the heaviest rains limited to a few localized areas, including the Tampa Bay region. Some of Tampa’s worst weather with Colin arrived with intense rainbands that continued to stream ashore Monday evening into Tuesday morning, long after Colin’s center had moved far to the north. Wind gusts hit 48 mph at Tampa’s Knight Airport just before 1 AM ET. CoCoRaHS reports through 7 AM ET Tuesday showed widespread 5” - 7” rainfall amounts over Pinellas and western Hillsborough Counties, including the Tampa and St. Petersburg areas. The heaviest rains had shifted just south of Tampa by late morning Tuesday. Two other pockets of heavy rain from Colin were in the eastern Florida Panhandle (including a CoCoRaHS report of 8.30” in northern Jefferson County) and in a belt across the far northern Florida peninsula (a whopping 10.95” in far southwest Alachua County).


Figure 4. 24-hour rainfall amounts from 8:00 AM EDT Monday, June 6, 2016, to 8 AM Tuesday, June 7. Image credit: NOAA/NWS Advanced Hydrologic Prediction Service

Named storms during the Atlantic winter: which year do they belong to?
Though it wasn’t a catastrophic event, Tropical Storm Colin made history in one way: Never before have we been tracking the Atlantic’s third named storm of a calendar year this early in the year. There have been just two other “C” storms as early as June since current naming practices began in the 1950s: Hurricane Chris (which began as a named subtropical storm on June 18, 2012) and Tropical Storm Candy (June 23, 1968). Going all the way back to 1851, the previous earliest appearance of the season’s third storm was June 12, 1887, although some early-season storms were undoubtedly missed during the pre-satellite era. What’s more, each of this year’s first three Atlantic named storms have all made landfall: Hurricane Alex in the Azores, Tropical Storm Bonnie in North Carolina, and Tropical Storm Colin in Florida.

It’s a truly impressive achievement to have our third named Atlantic storm of 2016—much less our third landfall—before we’re even halfway through June. But was Hurricane Alex really a 2016 event? One could make a case that extremely early tropical cyclones such as Alex are more closely tied to the previous year’s activity. The seasonality of hurricanes is driven in large part by sea surface temperature, which tends to hit its annual minimum around March in the Northern Hemisphere tropics and subtropics. This would suggest a physical rationale for defining a full-year hurricane season, at least for some research purposes, as running from March through February. In records going back to 1851, four tropical or subtropical cyclones of at least tropical storm strength have developed in January, and a tropical storm nicknamed the Groundhog Day storm developed on February 2, 1952. Then we find a gap until March 6, 1908, when a tropical storm that went on to become an unnamed Category 2 hurricane developed northeast of the Leeward Islands (oddly, this one headed southwest and ended up affecting the islands of Antigua and Basseterre). There is another large gap until the next-earliest tropical storm, Ana, which formed on April 20, 2003.

Based on these records, it could be argued that tropical cyclones in the Atlantic during January and early February, such as Alex, are more closely related to conditions found during the prior June-to-November season than to those that will prevail in the upcoming season. The same notion would apply to Hurricane Pali, which became the Central Pacific’s earliest named storm on record on January 7 of this year. An even more noticeable early-year minimum can be seen in statistics for the Northwest Pacific (see Figure 5 below), with the dip especially prominent because of the large number of tropical cyclones overall in that region. If we lived in the Southern Hemisphere, the calendar-year question would be a no-brainer, since the core of every season straddles two calendar years.

I checked in with Brian McNoldy (University of Miami/RSMAS) for his thoughts on calendar-year climatology. “I think most would agree that Alex was more a late-comer to the 2015 season than an early start to the 2016 season,” McNoldy said. Of course, it could be confusing if some researchers or agencies defined the Atlantic season in a calendar-year fashion while others used a different starting/ending date. “In the end,” McNoldy added, “there are so few extreme cases (Jan-Feb formations) that I doubt it would have any noticeable impact on climatology rankings or calculations.”



Figure 5. Seasonal climatology of tropical storms, typhoons, and super typhoons in the Northwest Pacific for the period 1959 - 2010. Image credit: NOAA/AOML.


Figure 6. Infrared satellite image from 1345Z (9:45 AM EDT) Tuesday, June 7, 2016, showing showers and thunderstorms associated with Tropical Storm Colin (top of image) and TD 1-E (bottom left, along and just off the southern coast of Mexico). Other showers and thunderstorms are associated with a disturbance in the Northwest Caribbean (center of image). Image credit: NASA/MSFC Earth Science Office.

TD 1E is born in the Northeast Pacific, but just barely
NHC began issuing advisories on Tropical Depression 1E, the first of the Northeast Pacific season, on Monday afternoon. TD 1E is associated with the same very broad channel of moisture that extends from the eastern Pacific all the way to Tropical Storm Colin (see Figure 6 above). As with Colin, TD 1E is a quite asymmetric system, with most of its convection concentrated on its east side. Between moderate wind shear and proximity to land, TD 1E is not expected to strengthen before it either dissipates or eases into the south coast of Mexico on Wednesday. Heavy rains and dangerous flash floods and mudslides are possible over the nearby mountainous terrain of southern Mexico and western Guatemala. Farther to the west, a disturbance located some 1400 miles southwest of Cabo San Lucas could undergo some slow development over the next couple of days, posing no threat to land.

Bob Henson

Hurricane Flood

Threat from TS Colin Shifts to Heavy Rain along Southeast U.S. Coast

By: Bob Henson , 4:22 AM GMT on June 07, 2016

Coastal residents from Georgia to North Carolina can expect to be deluged by rains associated with Tropical Storm Colin on Tuesday morning as the storm sweeps northeastward at an accelerating pace. In its advisory at 11 PM ET Monday, NOAA’s National Hurricane Center placed the center of Colin at 29.8°N, 83.8°W, or about 70 miles east of Apalachicola, FL, just offshore from the Big Bend Wildlife Management Area. Top sustained winds remained at 50 mph. Tropical storm warnings remained in effect along Florida's Gulf Coast from Indian Pass to Englewood and along the Southeast U.S. coast from Sebastian Inlet, FL, to Oregon Inlet, NC.


Figure 1. Angelo Memiakis, left, and Kelly Spiliotis work to deliver sandbags to the door jams of businesses along flooded Athens Street on Monday, June 6, 2016, in Tarpon Springs, FL, as Tropical Storm Colin barreled up the west coast of Florida. Residents on Florida's Gulf coast filled sandbags, schools closed early and graduation ceremonies were postponed as Gov. Rick Scott declared a state of emergency with Tropical Storm Colin churning toward the state Monday, threatening serious flooding. Image credit: Douglas R. Clifford/The Tampa Bay Times via AP.


FIgure 2. Satellite image of Tropical Storm Colin as of 12:07 am ET Tuesday, June 7, 2016.

Colin’s impact on Florida
Colin maintained its marked asymmetry throughout the day on Monday: even as it approached landfall, nearly all of Colin’s showers and thunderstorms were located east of its center (see Figure 2]. The storm's diffuse structure as it approached Florida helped cut its damage potential. As of late Monday, the severe weather impact of Colin on Florida had been minimal, with only a few reports of high wind and just one tornado reported (a waterspout moving onshore near Bonita Beach on Monday afternoon). Minor coastal flooding was widespread across Florida’s Gulf Coast as winds on the east side of Colin pushed water ashore. A storm surge of close to 3 feet was observed at Cedar Key, FL. Combined with high tide, the surge led to the highest water in years in the low-lying Cedar Key region, flooding a number of businesses and topping the water levels produced by Tropical Storm Debby in 2012.


Figure 2. Preliminary data show that a storm surge of around 3 feet (red curve minus blue curve) coincided with high tide (blue curve) on Monday afternoon, June 6, 2016, at Cedar Key, FL. Image credit: NOAA.


Figure 3. In a Monday evening outlook, NOAA’s Weather Prediction Center warned that a belt of 4” to 6” rains could fall along the immediate Southeast coast between 8 PM EDT Monday, June 6, 2016, and 8 PM Tuesday. Image credit: NOAA/NWS/WPC.

Coastal deluge in store for Southeast early Tuesday
Heavy rains developed on Monday as far northeast as North Carolina, more than 500 miles from Colin’s center. This pattern bears many of the hallmarks of a predecessor rain event (PRE), which can produce heavy rains a day or two ahead of the arrival of a tropical cyclone. PRE events typically feature a strong moisture channel extending northeastward from a tropical cyclone into a preexisting frontal zone and/or into an area of strong upward motion along the rear flank of a powerful upper-level jet stream (which was the case on Monday over the Carolinas).

Colin may have greater impact east of Florida than it did on the Sunshine State. Models agree that the storm should gain strength as it rockets northeastward parallel to the coast from Georgia to North Carolina on Tuesday morning. By the time it sweeps east of the NC Outer Banks on Tuesday afternoon, Colin could have winds on the high side of tropical storm strength, although by that point it will be evolving into a post-tropical cyclone. Flash flood watches are in effect from the northern Georgia coast to the Outer Banks, which have already been hard hit by torrential rains associated with Tropical Storm Bonnie. Cape Hatteras, NC, has received more than 6” of rain in the first six days of June after a record 12.67” in May, most of that during Memorial Day weekend.

I’ll have a full update on Colin--and on TD 1-E, the first tropical depression of the year in the Northeast Pacific--by midday Tuesday. We will also be posting updates on Colin at a WU liveblog.

Bob Henson



Hurricane Flood

Tropical Storm Colin Chugs Toward Florida, May Strengthen Off Southeast Coast

By: Bob Henson , 4:12 PM GMT on June 06, 2016

Despite its disorganized structure, ragtag Tropical Storm Colin gained a bit of strength Sunday night as it continued churning toward an expected landfall Monday night on the Big Bend of Florida’s northwest Gulf Coast. As of 11 AM EDT Monday, Colin was located at 27.0°N, 87.0°W, or about 285 miles west-southwest of Tampa, FL, moving north-northeast at 16 mph. Tropical storm warnings are in effect from Indian Pass to Englewood on the Florida Gulf Coast and from Sebastian Inlet, FL, to South Santee River, SC, on the Southeast U.S. coast. Colin’s top sustained winds increased to 50 mph overnight, leaving it in the weaker half of the tropical storm range. Little if any further intensification is expected before tonight’s landfall, as the storm’s structure is not conductive to strengthening. Vertical wind shear of 20 - 30 knots (25 - 35 mph) is helping to keep nearly all of Colin’s showers and thunderstorms (convection) displaced well to the east of the storm’s low-level center. The resulting comma shape starting to become evident on Monday morning is a classic marker of a tropical cyclone under the influence of increasing upper-level flow.


Figure 1. Infrared NOAA GOES image of Tropical Storm Colin as of 1445Z (10:45 am EDT) Monday, June 6, 2016. The center of Colin is faintly visible in the grey cloud mass just to the west of the bright red/orange area (which indicates very high, cold cloud tops). Image credit: NASA/MSFC Earth Science Office.


Figure 2. Unlike a more prototypical tropical cyclone, Colin features a broad area of southerly low-level winds ahead of its center, rather than winds across a large area rotating around its center. Shown here is data posted at 1502Z (11:02 AM EDT) Monday, June 6, 2016, from the Advanced Scatterometer (ASCAT) aboard the European Metop-A satellite. Image credit: NOAA/NESDIS and ASCAT/MetOp

Colin will sweep by Southeast U.S. coast over next 24 hours
Colin is being steered by a large area of southwesterly upper winds ahead of an upper-level trough extending from the northeast U.S. into the northwest Gulf of Mexico. This trough will keep the storm on a fairly well-defined track and will keep its structure asymmetric. A gradual curve to the right will take Colin across the Florida Peninsula overnight, with the storm emerging over the Atlantic just off the Southeast U.S. coast on Tuesday. Computer models agree that Colin will hug the coast while gaining forward speed on Tuesday, with the center likely just southeast of the Outer Banks by Tuesday afternoon and well east of the U.S. coast by Tuesday night. Tropical storm warnings may be extended northward along the Southeast coast, and Colin’s top sustained winds may actually increase slightly during the storm’s brief trek along the Southeast coast, as energy from upper levels feeds into Colin and the storm begins the process of transitioning into a post-tropical/extratropical cyclone. Because of the forward component of motion and the storm’s pre-existing asymmetry, the winds on Tuesday will be considerably stronger on the offshore side of Colin than on the coastal side. The well-defined steering currents will keep Colin from attempting any leftward curve that could hook it into the East Coast. Colin may reach its peak intensity as a strong tropical storm or post-tropical cyclone late Tuesday as it moves well east of the Outer Banks of North Carolina.


Figure 3. WU depiction of official forecast track of Tropical Storm Colin as of 11 AM EDT Monday, June 6, 2016.


Figure 4. Radar image for Tropical Storm Colin at 11:24 AM Monday, June 6, 2016. The image was produced using WU’s WunderMap with the “radar” feature turned on.

Torrential downpours will likely be the most widespread impact from Tropical Storm Colin. A large area of heavy rain on Monday morning extended from the Florida Panhandle into South Carolina, with intense rainbands streaming northward into Florida’s West Coast (see Figure 4 above). NOAA’s Storm Prediction Center has the northern half of Florida and far southeast Georgia in a slight risk for severe thunderstorms through Monday night, with a few tornadoes possible. As Colin sweeps to the northeast, heavy rain can be expected along the immediate Southeast coast late Monday night and Tuesday morning. Flash flood watches are in effect from the northern Georgia coast to the Outer Banks, which have already been hard hit by torrential rains associated with Tropical Storm Bonnie. Cape Hatteras, NC, has received 6.15” of rain in the first five days of June after a record 12.67” in May, most of that during Memorial Day weekend. This is already the second wettest June on record for Cape Hatteras (although the 14.34” racked up in June 1949 will be hard to top).

Storm surge risk along Florida’s Gulf Coast
Strong southwest flow on Colin’s east side may produce a storm surge along Florida’s Gulf Coast on Monday. The risk for high water will be greatest to the east of the eventual point of landfall, with more general enhancement along the coast several hours earlier, around the time of the mid-afternoon high tide. NHC is projecting a potential storm surge of 1 to 3 feet (perhaps higher in some areas) along the immediate coastline from Indian Pass south to Tampa Bay, with 1 to 2 feet possible south of Tampa Bay to Florida Bay. According to storm surge expert Hal Needham, the most vulnerable place for high water from Colin may be the Big Bend area from Apalachee Bay to Cedar Key, where the topography of the concave coast is especially conducive to producing surge. In a blog post published midday Monday, Needham projects a surge in the Cedar Key region of around 2.5 feet near high tide on Monday afternoon (around 3 PM EDT). Combined with tidal levels, this would produce a total water level (storm tide) at Cedar Key of around 4.7 feet above mean sea level (dubbed NAVD 88). This would be Cedar Key’s ninth highest storm tide in records going back to 1920, and it would be several inches higher than the water level produced in Cedar Key by Tropical Storm Debby in 2012.


Figure 5. If Tropical Storm Colin produces a peak storm tide on Monday afternoon of 4.72 feet, as projected by storm surge expert Dr. Hal Needham, it would be the ninth highest storm tide in records going back to 1920. This image was generated through Needham’s “U-Surge” dataset. Image credit: Hal Needham.

Colin is the earliest “C” storm in Atlantic history
Never before have we been tracking the Atlantic’s third named storm of a calendar year this early in the year. As noted in a weather.com article, there have been two other “C” storms as early as June since current naming practices began in the 1950s: Hurricane Chris (which began as a named subtropical storm on June 18, 2012) and Tropical Storm Candy (June 23, 1968). Going all the way back to 1851, the previous earliest appearance of the season’s third storm was June 12, 1887, although some early-season storms were undoubtedly missed during the pre-satellite era.

Bob Henson


Hurricane

Tropical Storm Colin Becomes Earliest “C” Storm in Atlantic History

By: Bob Henson , 1:50 AM GMT on June 06, 2016

NOAA’s National Hurricane Center upgraded Tropical Depression 3 to Tropical Storm Colin in a special update at 5:30 PM EDT Sunday, June 5--making some history along the way. Never before have we been tracking the Atlantic’s third named storm of a calendar year this early in the year. As noted in a weather.com article, there have been two other “C” storms as early as June since current naming practices began in the 1950s: Hurricane Chris (which began as a named subtropical storm on June 18, 2012) and Tropical Storm Candy (June 23, 1968). Going all the way back to 1851, the previous earliest appearance of the season’s third storm was June 12, 1887, although some early-season storms were undoubtedly missed during the pre-satellite era.

As of 8 PM EDT Sunday, Tropical Storm Colin was located in the south central Gulf of Mexico at 23.4°N, 87.8°W, or about 460 miles southwest of Tampa, Florida. Colin is a minimal tropical storm, with top sustained winds of just 40 mph, and only modest further strengthening is expected before Colin approaches the northwest Gulf Coast of the Florida peninsula on Monday evening. The well-defined southwesterly flow steering Colin will take it into the Atlantic and on a track paralleling the southeast U.S. coast on Tuesday, where models suggest it will maintain or regain tropical storm strength, especially southeast of North Carolina. Update: At 11:00 PM EDT Sunday, NHC placed the southeast U.S. coast from Sebastian Inlet, FL, to Altamaha Sound, GA, under a tropical storm warning, with a tropical storm watch extending northward from the warning area to the South Santee River, SC. A tropical storm warning remains in effect on the Florida Gulf Coast from Indian Pass to Englewood.

As shown in Figure 1, the steering flow will keep Colin moving northeast rather than curving north or northwest toward the U.S. East Coast. The storm’s heaviest rains will likely remain just off the Southeast coast, although residents along the immediate coast should be prepared for tropical storm conditions and heed precautions as recommended by local authorities.


Figure 1. WU depiction of official forecast track of Tropical Storm Colin as of 8 PM EDT Sunday, June 6, 2016.


Figure 2. This enhanced infrared satellite image of Tropical Storm Colin from 8:37 PM EDT Sunday, June 6, 2016, shows convection blossoming (red and yellow colors) south of Colin’s center of circulation. Image credit: CSU/CIRA/RAMMB.


Colin has a quite elongated, asymmetric structure, with most of its showers and thunderstorms (convection) on its east flank, although very strong convection was beginning to bubble on Colin’s south side on Sunday evening (see Figure 2 above) as the circulation moves away from the Yucatan Peninsula. The nighttime burst in convection common to tropical storms will give Colin an opportunity to strengthen overnight over very warm waters of around 28°C (82-83°F). On Monday, wind shear will increase along Colin’s track toward the Florida coast (see Figure 4 below), which will limit the storm’s ability to strengthen further. The shear will also tend to favor a continuation of Colin’s asymmetric structure.


Figure 3. A plethora of watches, warnings, and advisories covered the central Florida peninsula and nearby waters on Sunday evening, June 5, 2016. Image credit: NWS.


Despite its modest strength, Colin may pack a noteworthy punch across Florida over the next day or so. Intense thunderstorms can be expected to race northward across the peninsula from Sunday night through Monday. Some of these may spawn tornadoes, as the vertical wind shear that limits Colin’s growth as a tropical system will also favor the development of rotating updrafts within thunderstorms. At high tide early Monday afternoon, a storm surge of 1 to 3 feet (perhaps higher in some areas) could affect the immediate coastline from Indian Pass south to Tampa Bay, with 1 to 2 feet possible south of Tampa Bay to Florida Bay. Very heavy rains are also on tap for much of the peninsula, with amounts easily topping 6” to 8” in localized areas.

We’ll have a full update on Colin by midday Monday. We are also keeping our eye on two areas of potential tropical development in the Northeast Pacific, although the odds are slim that either one will develop over the next two to three days.

Bob Henson


Figure 4. As it moves northward toward the west coast of Florida, Tropical Storm Colin will encounter increasing vertical wind shear (shown here in knots; multiply by 1.15 for mph). This wind shear will limit Colin’s ability to strengthen before it strikes the Florida coast. Image credit: University of Wisconsin/SSEC.

Hurricane

TD 3 Forms in SE Gulf; Tropical Storm Warnings on Florida Gulf Coast

By: Bob Henson , 5:14 PM GMT on June 05, 2016

A large swath of coastline from the Florida panhandle to the state’s west coast was placed under a tropical storm warning on Sunday morning by the National Hurricane Center (NHC) with the commencement of advisories for newly declared Tropical Depression 3, expected to become Tropical Storm Colin by Sunday night. The tropical storm warning extends from Indian Pass (southeast of Panama City) to Englewood (between Tampa and Fort Myers). As of 11 AM EDT Sunday, the center of circulation for TD 3 was located just off the north coast of Mexico’s Yucatan Peninsula, or about 550 miles southwest of Tampa, FL. Virtually all of the shower and thunderstorm activity (convection) associated with TD 3 was positioned more than 100 miles east of this center, over the very warm waters of the Yucatan Channel, the extreme southeast Gulf of Mexico, and the northwest Caribbean (see Figure 1 below). The convection was broadening and intensifying on Sunday, suggesting that TD 3 is approaching tropical storm strength.


Figure 1. Visible satellite image of TD 3.


Figure 2. WU tracking map for Tropical Depression 3 based on the forecast issued by NOAA/NHC at 11 AM EDT Sunday, June 5, 2016.

The wide extent of TD 3’s convection could have set the stage for a large and powerful hurricane if the system had a long time to organize under favorable conditions. However, larger tropical depressions tend to take longer than smaller ones to consolidate their energy, and TD 3 will not have a great deal of time before it moves inland. Models have been quite consistent in making TD 3 a weak or moderate tropical storm prior to landfall, including HWRF, the top-performing intensity model of 2015.

A broad southwest flow at upper levels will channel TD 3 toward the upper west coast of Florida, with landfall possible as soon as Monday evening, perhaps in the sparsely populated Big Bend section of Florida’s coast. There is high confidence on this general track, with the large-scale features driving it already in place and model guidance holding firm. The large southward extent of the tropical storm warning reflects the storm’s marked asymmetry, which will keep the heaviest thunderstorms and the highest winds well to the east of the center. There is a chance that the low-level center of circulation of TD 3 could reorganize beneath the heaviest convection, which might result in a landfall closer to the southern part of the warning area. However, any such shift would result in a shorter track over water, which would give TD 3 even less time to organize over the Gulf. Hurricane hunters from the U.S. Air Force were en route to TD 3 early Sunday afternoon; the data they collect should give us a better sense of TD 3’s structure and its potential for strengthening.


Figure 3. Infrared NOAA GOES image of TD 3 as of 1600Z (noon EDT) Sunday, June 5, 2016. Image credit: NASA/MSFC Earth Science Office.

Potential impacts in Florida
High tides on Florida’s west coast are at their highest values of the month because of this weekend’s new moon, so even a weak Tropical Storm Colin could produce noticeable storm surge flooding. NHC is predicting that water heights at high tide along the immediate coast could reach 1 to 3 feet above ground level from Indian Pass south to Tampa Bay and 1 to 2 feet above ground level from Tampa Bay south to Florida Bay.

Regardless of its exact track and strength, TD 3 will bring very heavy rains across much of Florida, especially on Sunday night and Monday. There is some risk of nocturnal tornadoes over South Florida on Sunday night, as southeasterly low-level flow is overtopped by stronger southwest flow at upper levels. Here and throughout the state, convection will be fueled by a swath of extremely rich tropical moisture moving north from the Caribbean. On Monday, the bulk of the Florida peninsula will be swaddled by an air mass with precipitable water between 2.00” and 3.00”. These PW amounts could match or exceed record values for late spring and early summer at several locations. (Precipitable water, or PW, is the amount of moisture in the atmosphere in the form of water vapor above a given point.) Rainfall amounts are likely to be in the 4” - 6” range on the right-hand side of TD 3’s track across central and/or northern Florida, with isolated 6” - 10” amounts possible.


Figure 4. Projected rainfall for the period 8 AM EDT Sunday, June 5, 2016, through 8 AM Wednesday, June 8. Image credit: NOAA/NWS.

After the Florida landfall, what next?
TD 3 may reach its maximum strength after it traverses Florida rather than beforehand. Nearly all models are predicting that TD 3 will restrengthen after it emerges off the east coast of Florida, so we could be dealing with a Tropical Storm Colin roughly paralleling the southeast U.S. coast on Tuesday. Here again, the lopsided structure of TD 3 will tend to keep the heaviest thunderstorms and strongest winds on the offshore (southeast) side of the center, which would minimize any potential impact from Georgia to North Carolina even if the center were to hug the coastline. Steering flow around a large eastern U.S. trough means there is very high confidence in the overall northeastward direction of motion. By Wednesday, the system is expected to be shooting northeastward between Bermuda and Nova Scotia as it rapidly evolves into a post-tropical storm.

I’ll be back with a brief update on Sunday night should TD 3 be upgraded to Tropical Storm Colin, with our next full update midday Monday. One other note: residents of the mid-Atlantic should be on alert for potentially severe thunderstorms on Sunday afternoon and evening. The NOAA Storm Prediction Center has an enhanced risk of severe weather (see map below) extending from central North Carolina to central New Jersey, including the Washington, D.C., and Philadelphia metro areas. Damaging winds and a few tornadoes are possible with the strongest storms.

Bob Henson




Hurricane

Florida West Coast In Sights of Potential Tropical Storm

By: Bob Henson , 7:15 PM GMT on June 04, 2016

A landfalling tropical depression or tropical storm appears increasingly likely to affect the west coast of Florida early in the coming week. On Saturday afternoon, a large tropical wave dubbed Invest 93L was gradually organizing as it moved into the Northwest Caribbean, with an extensive area of convection (showers and thunderstorms) evident on the system’s eastern side (see Figure 1 below). A center of low pressure just beginning to form within this tropical wave is expected to move northward along or just inland from the east coast of Mexico’s Yucatan Peninsula, then emerge late Sunday or Monday in the southeastern Gulf of Mexico. In an outlook issued at 2 PM EDT Saturday, the National Hurricane Center gave this system 70 percent odds of developing into a tropical cyclone by Monday evening and an 80 percent chance by Tuesday evening.


Figure 1. Infrared NOAA GOES image of the tropical wave over the Northwest Caribbean as of 1830Z (2:30 pm EDT) Saturday, June 4, 2016. Widespread showers and thunderstorms are concentrated on the east side of the developing center of low pressure. Image credit: NASA/MSFC Earth Science Office.

Track and intensity outlook
The steering flow that will drive this system is fairly straightforward, as an intensifying upper low across the northeast U.S. is joining forces with a weak but persistent upper low over Texas that has fueled heavy rain and deadly flooding over the last week. Given the large channel of southwesterly upper-level flow that will prevail across the Gulf of Mexico, models are in strong agreement that the expected tropical cyclone would move northeast and make landfall along the middle or upper west coast of Florida, most likely on or around Tuesday. If it does become a tropical storm, it will be named Colin—which would be the earliest we have reached the “C” name since Atlantic hurricanes have been named, and the earliest third storm of the calendar year in all recorded storms since 1851, beating an unnamed storm that formed on June 12, 1887.

Although the track of potential Colin-to-be is fairly well defined, there is a bit more uncertainty on how strong it might be. Much will depend on whether the northward movement of the low pressure center ends up off the Yucatan coast, near the coast, or well inland. The greater the interaction with the Yucatan, the more the system will struggle to develop. Even accounting for a good bit of land interaction, conditions will be quite favorable for the system to strengthen after it moves into the southeastern Gulf. Wind shear will be fairly low (the SHIPS model predicts 5 - 10 knots), and above-average sea surface temperatures of around 28°C (82 - 83°F) are more than warm enough to support intensification. However, the system will have only about 36 to 48 hours over the eastern Gulf, which will most likely keep its maximum strength within the tropical storm range. In addition, wind shear will increase to moderate or strong levels as the system moves toward the west coast of Florida ahead of the approaching upper trough.

Hurricane intensity forecasting has improved notably in the 2010s, as Jeff Masters and I discussed in detail in a blog post on May 6. The best-performing intensity model in 2015 was HWRF, and the last several runs of the HWRF through 12Z Saturday morning have brought this system into the 40 - 50 knot range (45 - 55 mph) just before landfall. The GFS model has also been consistent in calling for a weak to moderate tropical storm at landfall. We should have a better handle on this system’s potential strength after it clears the Yucatan. Should it enter the Gulf in a relatively organized state, I would not rule out the possibility of a higher-end tropical storm.


Figure 3. 5-day rainfall projection issued by NOAA/NWS Weather Prediction Center for the period from 8:00 am Saturday, June 4, 2016, through 8:00 am Thursday, June 9. Image credit: NOAA/NWS/WPC.

Even a weak tropical storm could cause significant water issues
Several factors may come together to produce more coastal and inland flood impacts than one might expect. The potential Colin is likely to be a somewhat asymmetric storm, with the strongest winds and heaviest rains on its east side. This would push water toward the central and northern Gulf Coast of the Florida peninsula at the same time that very heavy rain is falling in some areas. A system developing this quickly and remaining near hurricane strength would not pack a major storm surge, especially away from its immediate landfall location. If a Tropical Storm Colin developed and made landfall in Florida’s sparsely populated Big Bend, as consistently projected by the GFS and ECMWF models, this would further reduce the threat of any major surge impacts. However, Tampa will be on the stronger southeast side of the system, and the eventual track could end up closer to Tampa, as suggested by the 12Z Saturday HWRF run. Even a minor storm-enhanced tide could have noticeable impacts in the highly populated Tampa Bay area, which has been designated the nation’s most vulnerable location to higher-end storm surge (not expected with this system). The highest astronomical tides of the month in Tampa—around 3 feet above the average lowest tide (mean low low water)—occur with the new moon, which will be occurring this weekend. Regardless of its strength as a tropical cyclone, the now-developing system is likely to bring very heavy rains across a swath through central and northern Florida (see Figure 3 above), which would only exacerbate the flood potential.


Figure 4. Track of all tropical storms and hurricanes recorded during the month of June (1851-2015) over the Gulf of Mexico and northwest Caribbean. The color code at right shows each system’s strength (blue = tropical depression, green = tropical storm, yellow = Category 1 hurricane, etc.) Image credit: NOAA Historical Hurricane Tracks.

June favors tropical storms in the eastern Gulf of Mexico
The projected track of the developing tropical cyclone is right on target with climatology, which shows a favored track northward through the eastern Gulf of Mexico. Few of these systems make landfall on the Florida peninsula, though. The only hurricane known to strike Florida’s West Coast in June was an unnamed Category 1 hurricane that made landfall on June 24, 1945, between Tampa and Cedar Key, causing relatively minor damage (see yellow track on Figure 4 above). Tampa recorded a 24-hour calendar-day rainfall of 9.88” on June 23, 1945, which remains the area’s second-highest calendar-day total (topped only by 11.45” on May 8, 1979). This hurricane weakened to a tropical storm while crossing the Florida peninsula, then regained hurricane strength after it moved offshore and made a second landfall, crossing the Outer Banks of North Carolina. It is too soon to know how far north a potential Tropical Storm Colin would track if it were to emerge as a tropical cyclone off the East Coast of Florida, although the predicted strong trough over the eastern U.S. would keep it from threatening the Northeast.


Figure 5. Visible satellite image showing a compact swirl of mostly mid-level clouds around Tropical Depression Bonnie at 1838Z (2:38 pm EDT) Saturday, June 4, 2016.

Bye-bye, Bonnie
As it continued moving eastward hundreds of miles from the Carolina coast, pesky Tropical Depression Bonnie put forth an unexpected burst of convection Friday afternoon and evening, helping push it back up to minimal tropical-storm status. The growth spurt was futile, though, as increasing wind shear and a track toward colder water is sealing Bonnie’s fate. NHC demoted Bonnie once again to tropical depression status at 11 AM EDT Saturday, with further degradation to a post-tropical low expected by Sunday. If nothing else, Bonnie plus the potential Colin may give us a surprisingly large number of days with active tropical cyclones in the Atlantic basin for late May and early June.

Eastern Pacific's 91E could still become a tropical cyclone
In the Eastern Pacific, Invest 91E is taking its time organizing. Satellite loops show that an area of heavy thunderstorms located about 1100 miles south-southwest of the southern tip of the Baja Peninsula at 2 PM EDT Saturday has enlarged but not improved significantly in organization since Friday. This disturbance may still develop into the Eastern Pacific's first tropical cyclone of the year over the next couple of days before conditions become less favorable for development. Moving west at about 10 - 15 mph, the system is not a threat to any land areas. NHC now has 50-50 odds that 91E will develop into a tropical cyclone in the next 2 to 3 days. Should 91E become a tropical storm, it would be named Agatha. The first named storm of the year in the Eastern Pacific typically forms on June 10, so we would be very close to the climatological pace we expect. An even weaker system located several hundred miles south-southeast of Acapulco has a slight chance of intensifying over the next couple of days as it brings locally heavy rains to parts of extreme southern Mexico and Guatemala.

I’ll be back with an update by Sunday afternoon, while Jeff Masters is on long-scheduled travel over the coming week.

Bob Henson

Hurricane

Tropical Storm Possible in the Gulf of Mexico by Monday

By: Jeff Masters and Bob Henson , 4:12 PM GMT on June 03, 2016

A concentrated area of heavy thunderstorms has developed over the Western Caribbean, and this system has the potential for development into a tropical depression on Sunday or Monday. Wind shear was a high 30 knots on Friday morning over the region. This high shear will prevent development until Saturday at the earliest as the disturbance heads west-northwest towards Mexico's Yucatan Peninsula. On Saturday and Sunday, shear will drop and an area of low pressure will form over the waters of the Gulf of Mexico and Western Caribbean near the Yucatan Peninsula. This low and its associated moisture will ride up to the north-northeast into the southern Gulf of Mexico on Sunday under the steering influence of a large trough of low pressure that will move over the central Gulf of Mexico. Our three top models for predicting tropical cyclone genesis--the GFS, European, and UKMET models--all showed a tropical depression or tropical storm developing by Monday and making landfall on the west coast of Florida north of Tampa on Tuesday morning. There will be some high wind shear and dry air over the central Gulf of Mexico early next week in association with the upper-level trough of low pressure there, and these conditions will likely interfere with development, making intensification into a hurricane unlikely. Regardless of development, heavy rains will be the main threat from this system, and  2 - 7" of rain can be expected over much of Florida during the period Monday - Tuesday. In their 8 am EDT Friday Tropical Weather Outlook, NHC gave 2-day and 5-day odds of development of 10% and 60%, respectively. Should this system get a name, it would be Colin. Hurricane Hunters are now scheduled to investigate the Northwest Caribbean disturbance on Saturday afternoon.


Figure 1. Predicted precipitation for the 5-day period ending 8 am Wednesday, June 8, 2016. A tropical disturbance is predicted to bring rainfall amounts of 2 - 7" inches to most of Florida, with most of the rain falling Monday and Tuesday. Image credit: National Weather Service.

Eastern Pacific's 91E could become a tropical depression this weekend
In the Eastern Pacific, satellite loops show that an area of heavy thunderstorms located about 975 miles south-southwest of the southern tip of the Baja Peninsula at 8 am EDT Friday has not improved in organization over the past two days. However, this disturbance (91E) is still likely to develop into the Eastern Pacific's first tropical cyclone of the year this weekend, according to recent runs of the GFS and European models. The disturbance is moving west-northwestward at about 10 - 15 mph, and is not a threat to any land areas. In their 8 am EDT Thursday Tropical Weather Outlook, NHC dropped their 2-day and 5-day odds of development to 40% and 60%, respectively. Should 91E become a tropical storm, it would be named Agatha. The first named storm of the year in the Eastern Pacific typically forms on June 10, so we would be very close to the climatological pace we expect.

Bonnie back on the downswing
After re-consolidating east of North Carolina on Thursday and approaching tropical storm strength, Tropical Depression Bonnie is now on its last legs. Satellite loops show that shower and thunderstorm activity has diminished greatly over the last few hours. Upper-level west-to-east flow just to the north of Bonnie will exert an increasing amount of wind shear over the next 24 hours while dragging the system out to sea. In its 11 AM EDT Friday update, the National Hurricane Center predicts that Bonnie will degenerate to a remnant low by Saturday morning before dissipating over the weekend. Residents of eastern North Carolina will no doubt be relieved to have Bonnie out of their hair as the weekend approaches. Cape Hatteras, NC, saw 8.41” of rain during the last four days of May and another 5.74” in the first two days of June. Last month was the wettest May in 124 years of weather records at Cape Hatteras, with a total rainfall for the month of 12.67”.

Severe weather taking aim on the mid-Atlantic for Sunday
A much different threat will be heading toward the mid-Atlantic region on Sunday. NOAA’s Storm Prediction Center has placed the area from northeast North Carolina to far southern Pennsylvania, including the Washington, D.C., area, under an enhanced risk of severe weather (the third of five risk levels) for Sunday. A surrounding slight-risk area extends from eastern Georgia to northern Pennsylvania and New Jersey, including more than 28 million people. Sunday’s set-up will be driven by very unstable air already in place across most of the region, coupled with favorable vertical wind shear and a sharp upper-level trough moving in on Sunday during peak daytime heating. The situation favors supercell thunderstorms in the afternoon and evening, and all modes of severe weather--including tornadoes, large hail, and damaging winds--are possible. In the shorter term, NOAA/SPC is calling for a slight risk of severe weather on Friday across Iowa and southern Minnesota, associated with the same front and upper-level trough that will head for the East Coast this weekend.


Figure 2. WU depiction of the Day 3 severe weather outlook issued by the NOAA/NWS Storm Prediction Center on Friday, June 3, 2016, and valid for Sunday, June 5.

Tragic deaths in Texas as widespread flooding continues
Five U.S. Army soldiers have been confirmed dead, and four others remained missing on Friday morning, after their vehicle (a troop carrier, resembling a flatbed truck) flipped and was swept away while crossing a creek as part of a training exercise on the grounds of Fort Hood in central Texas. Three other soldiers were rescued, and the Army will be investigating the incident. Officials at a press conference on Friday morning said the crossing at Owl Creek was not designated as a low-water crossing. The incident is a sad reminder of the power of flowing water, which pays no respect to any laws other than those of physics. In an excellent Forbes commentary last April, Marshall Shepherd discussed the counterintuitive strength of even a small amount of water on a roadway. Shepherd linked to a very useful physics-based discussion from Steve Waters, a senior hydrologist at the Flood Control District of Maricopa County (AZ), explaining why flowing water is so powerful and dangerous. The risks include not only the sheer weight of water (62.4 pounds per cubic foot) and the loss of roadway friction, but also the buoyancy factor. Every foot of water rising against the cab of a vehicle allows the vehicle to displace 1,500 pounds of water--effectively reducing the car’s weight by 125 pounds for every inch that water rises around its sides. Two feet of water is enough to float most automobiles, and once a vehicle is free-floating, it will tend to shift toward the fastest-flowing currents. High-clearance trucks with big cabs are hardly invulnerable once the water reaches their sides, since these vehicles displace even more water per foot of rise.


Figure 3. The streets of this neighborhood in Spring, TX (near Houston), became waterways on Thursday, June 2, 2016. Image credit: wunderphotographer threeyellowstarfish.


Figure 4. NOAA satellite image at 1515Z (10:15 am CDT) Friday, June 3, 2016, showing the mid-level circulation across north central Texas and the heavy rains located well to the southeast. Image credit: NCAR/RAL Real-Time Weather Data

A massive gyre of rainfall, with embedded torrential cells, swung northeast across central and eastern Texas on Thursday. The heaviest amounts recorded by the CoCoRaHS volunteer network on Friday morning were west of Fort Worth (6.98” reported in far northeast Callahan County) and from Houston northeast (several reports of 4” - 6”). A mesoscale convective vortex was clearly visible just west of the Dallas-Fort Worth area on Friday morning (see Figure 4), while the heaviest rains had pushed into southwest Louisiana and the northwest Gulf of Mexico by Friday morning. Rain-cooled air has helped to stabilize conditions across Texas, but the central third of Texas and southern Louisiana are still covered by flash flood watches: localized heavy rains are possible into the weekend, and it won’t take much additional rain atop the saturated ground to cause flooding problems.

We’ll be keeping tabs on the potential development in the Atlantic and Pacific through the weekend. Our next post will be midday Saturday.

Jeff Masters and Bob Henson

Hurricane Flood Extreme Weather

Tropical Threat to Florida Next Week; Floods Persist in Texas, Europe

By: Jeff Masters and Bob Henson , 4:16 PM GMT on June 02, 2016

The next named storm for the Atlantic will be named Colin, and there is one potential area to watch for its development early next week: over the Western Caribbean, where a large area of low pressure laden with plenty of tropical moisture is expected to form. This low and its associated moisture will ride up to the north-northeast into the southern Gulf of Mexico on Sunday, and start spreading heavy rains over Florida on Monday. About 10% - 30% of the members of the ensemble runs of the 00Z Thursday GFS and European models showed a tropical depression forming in the Gulf of Mexico or Western Caribbean near Mexico's Yucatan Peninsula early next week, with the storm making landfall along the west coast of Florida on Tuesday. There will be some high wind shear and dry air over the central Gulf of Mexico early next week in association with an upper-level trough of low pressure, and these conditions will likely interfere with development, making intensification into a hurricane unlikely. Regardless of development, heavy rains will be the main threat from this system, and  3 - 5" of rain can be expected over much of Florida during the period Monday - Tuesday. In their 8 am EDT Thursday Tropical Weather Outlook, NHC gave 2-day and 5-day odds of development of 0% and 30%, respectively. Given that the 00Z Thursday runs of all three of our reliable models for predicting tropical cyclone genesis--the GFS, European, and UKMET models--all showed some degree of development, I think the 5-day odds of development should be bumped up to 40%.

If Colin were to develop next week, it would be the earliest occurrence of the third Atlantic tropical storm of a calendar year in records going back to 1851, beating out an unnamed storm from June 12, 1887. One important caveat is that systems as weak as Bonnie could easily have been missed or underreported in the era before satellite observations.


Figure 1. Predicted precipitation for the 7-day period ending 8 am Thursday, June 9, 2016. A tropical disturbance is predicted to bring rainfall amounts of up to 3 - 5" inches to most of Florida, with most of the rain falling Monday and Tuesday. Image credit: National Weather Service.


Figure 2. Surface wind depiction of Tropical Depression Bonnie at 7 am EDT June 2, 2016, from earth.nullschool.net.

Bonnie is back
Bonnie came back to life as a tropical depression near the Outer Banks of North Carolina at 11 am EDT Thursday, when NHC began issuing advisories on the system again. Satellite loops on Thursday morning showed that Bonnie had regained its closed surface circulation, with a modest area of heavy thunderstorms near the center. These thunderstorms will likely bring 1 - 3" of rain to the Outer Banks of North Carolina through Thursday night. Bonnie is headed east-northeast out to sea, and will not cause any more trouble to land areas after Thursday. Bonnie will be under light wind shear and over the relatively warm 26°C (79°F) waters of the Gulf Stream through Thursday night, which may allow intensification to a minimum-strength tropical storm with 40 - 45 mph winds by Friday morning. Later on Friday, Bonnie will encounter waters of 24°C (75°F) and cooler, which should cause dissipation by this weekend.

The 2016 version of Tropical Storm Bonnie was the seventh incarnation of the storm, which made its first appearance back in 1980. Only five other Atlantic storms have had more appearances than Bonnie--Arlene with ten, Florence with nine, Cindy with eight, Dolly with eight, and Frances with eight. The seven versions of Bonnie have made landfall in six different years (if we include landfalls at tropical depression strength). Only two other named storms, Arlene and Beryl, have also made landfalls as a tropical depression or stronger in as many as six different years:

BONNIE – 1980 – No; 1986 – Landfall Texas; 1992 – Landfall Crossing the Azores; 1998 – Landfall North Carolina; 2004 – Landfall Florida; 2010 – Landfall Florida; 2016 Landfall as Tropical Depression, South Carolina.

ARLENE – 1959 – Landfall Louisiana; 1963 – Landfall Bermuda; 1967 – No; 1971 – No; 1981 – Landfall Cuba; 1987 – No; 1993 – Landfall Texas; 1999 – No; 2005 – Landfall Florida; 2011 – Landfall Mexico.

BERYL – 1982 – Landfall Cape Verde Islands; 1988 – Landfall New Orleans; 1994 – Panama City, Florida; 2000 – Landfall Mexico; 2006 – Landfall Nantucket; 2012 – Jacksonville Beach, Florida.
 
Thanks go to wunderground member Mark Cole for these stats.

First tropical depression of the season likely in the Eastern Pacific this weekend
In the Eastern Pacific, satellite loops show that an area of heavy thunderstorms located about 1000 miles south-southwest of the southern tip of the Baja Peninsula has not improved in organization over the past day. However, this disturbance (91E) is likely to develop into the Eastern Pacific's first tropical cyclone of the year this weekend, according to recent runs of the GFS and European models. The disturbance is moving west-northwestward at about 10 - 15 mph, and is not a threat to any land areas. In their 8 am EDT Thursday Tropical Weather Outlook, NHC gave 91E 2-day and 5-day odds of development of 70% and 90%, respectively. Should 91E become a tropical storm, it would be named Agatha. The first named storm of the year in the Eastern Pacific typically forms on June 10, so we would be very close to the climatological pace we expect.


Figure 3. An aerial view of homes in the Horseshoe Bend area on the banks of the Brazos River in north central Texas on Wednesday, June 1, 2016. Residents of some rural southeast Texas counties braced for more flooding along the river that is expected to crest at a record level just two years after it had run dry in places because of drought. (Brandon Wade/Star-Telegram via AP)

Deep water in the heart of Texas
Heavy rains continue to plague much of the Southern Plains, thanks to a weak, slow-moving upper-level low parked over west Texas and a persistent feed of very rich tropical air into the region from the Caribbean and Gulf of Mexico. The upper low will trudge toward central and eastern Texas by Friday, then stall out before drifting southwest. Eventually, the low will get sheared out and/or picked up by a stronger upper trough moving through the eastern U.S. Until then, Texas will be vulnerable to multiple rounds of heavy thunderstorms packing torrential rain. After the Brazos River west of Houston hit a record crest on Monday (with levels reaching a new peak on Thursday), the river overflowed more than 200 miles to the northwest, in Parker County west of Fort Worth, overnight Tuesday night (see Figure 3). On Wednesday afternoon, flash floods pounded the Lubbock area as an estimated 3” to 5” of rain fell over parts of the city in a two-hour period. Overnight on Wednesday night, a mesoscale convective system (MCSs) formed over central Texas. After dumping more than 4” over parts of the San Antonio area, this MCS was drifting north on Thursday morning, while new showers and storms were developing to its east in the Houston area.

The exact location of the heaviest Texas downpours amid more general rains will evolve over the next couple of days based on where rain-cooled outflow and other hard-to-predict small-scale weather features set up. The high-resolution HRRR model indicates that Thursday’s heaviest rain will push northeast toward Louisiana, Arkansas, and Oklahoma late in the day, with the 4-km NAM model suggesting another MCS will bloom around the pre-existing circulation over central TX by Friday. Flash flood watches are plastered across much of central TX and OK, and river flooding may become an increasing concern as the wet days roll onward.


Figure 4. Infrared satellite imagery from NOAA’s GOES satellite shows a mesoscale convective complex over central Texas at 1415Z (10:15 am EDT) Thursday, June 2, 2016. Additional thunderstorms were forming over southeast TX. Image credit: NASA/MSFC Earth Science Office.

Historic flooding across France, Germany
The death toll from a week of flooding rose to at least nine on Thursday as torrential rains continued to inundate parts of northwest Europe. Warm, moist air has been flowing into the region around a cut-off upper low located near Austria. With the low stranded in place, thunderstorms have been recurring day after day, with severe weather threats extending across much of the continent on Thursday (see Figure 5).


Figure 5. Severe weather outlook for Europe issued early Thursday, June 2, 2016. Image credit: European Storm Forecast Experiment (ESTOFEX).


Some of the worst flash flooding on Wednesday was in parts of southern Germany. The town of Simbach am Inn was devastated by flood waters that cascaded through the center of town, tossing vehicles and leaving behind mounds of debris (see Figure 6 below). At least three people were killed in Simbach am Inn, with several others missing.

Meanwhile, central France has been hit hard by river flooding, where water levels have toppled century-long records in some places. Flood guidance on Thursday from the French agency VIGICRUES targeted the region from Paris south through the Loire Valley as one of the highest-risk zones. Record crests from 1910 have already been broken along the Loing, a tributary of the Seine. Thousands of people have been evacuated across the region. On Thursday, some riverbank sections along the Seine in central Paris were already closed as water flowed into the region from the south. One of the city’s most renowned benchmarks of high water is the statue of a Zouave soldier at the Pont de l’Alma, built in the 1850s. The statue’s feet were covered on Thursday as the water height reached 4.45 meters, its highest level since at least 2001. During the city’s flood of record, in 1910, the water level reached the statue’s shoulders (8.62 meters). The Seine is predicted to crest between 5 and 6 meters on Friday, according to Le Monde. The Guardian has a powerful gallery of flood-related images from Germany and France.

Jeff Masters (tropical], Bob Henson [flooding]


Figure 6. Firemen rescue two women with their boat following heavy floods the day before on June 2, 2016 in Simbach am Inn, Germany. Flash floods from the swollen Inn river took local communities by surprise, trapping children at schools and forcing some residents to flee to their rooftops. Image credit: Sebastian Widmann/Getty Images.


Figure 7.. A man stands on a road flooded by the river Seine after its banks became flooded following heavy rainfalls in Paris on June 2, 2016. Torrential downpours have lashed parts of northern Europe in recent days, leaving four dead in Germany, breaching the banks of the Seine in Paris and flooding rural roads and villages. Image credit: Geoffroy Van der Hasselt/AFP/Getty Images.

Hurricane Flood Extreme Weather

CSU Calls for Near-Average 2016 Atlantic Hurricane Season; Ex-Bonnie Tries a Comeback

By: Jeff Masters and Bob Henson , 4:14 PM GMT on June 01, 2016

The 2016 Atlantic hurricane season is off to an early start, with two named storms already in the books before the official June 1 start of the season: Hurricane Alex in January, and Tropical Storm Bonnie in May. Despite this early-season activity, a near-average Atlantic hurricane season is likely in 2016, said Dr. Phil Klotzbach of Colorado State University (CSU) in his latest seasonal forecast issued June 1. The CSU forecast is calling for an Atlantic hurricane season with 14 named storms, 6 hurricanes, 2 major hurricanes, and an Accumulated Cyclone Energy (ACE) of 94 (these numbers all take Alex and Bonnie into account.) The long-term averages for the period 1971 - 2010 were 12 named storms, 6.5 hurricanes, 2 major hurricanes, and an ACE of 92. The CSU outlook also calls for a 50% chance of a major hurricane hitting the U.S. in 2016, with a 30% chance for the East Coast and Florida Peninsula and a 29% chance for the Gulf Coast. The Caribbean is forecast to have a 40% chance of seeing at least one major hurricane. All of these probabilities are very close to the long-term numbers from the last century, and the forecast as a whole is largely consistent with CSU’s extended-range forecast issued on April 14. This is the 33rd year CSU has issued a seasonal hurricane forecast, but the first forecast done without Dr. Bill Gray as a main author, as he passed away on April 17.

Five years were selected as “analogue” years that the 2016 hurricane season may resemble:

1973 (8 named storms, 4 hurricanes, and 1 major hurricane)
1978 (11 named storms, 5 hurricanes, and 2 major hurricanes)
1983 (4 named storms, 3 hurricanes, and 1 major hurricane)
1992 (7 named storms, 4 hurricanes, and 1 major hurricane)
2003 (16 named storms, 7 hurricanes, and 3 major hurricanes)

These seasons were characterized by El Niño conditions in the previous winter that transitioned to either neutral or La Niña conditions by summer/autumn, and all had generally cool sea surface temperatures (SSTs) in the far North Atlantic and near-average tropical Atlantic SSTs during hurricane season. The average activity for these years was 9.2 named storms, 4.6 hurricanes, and 1.7 major hurricanes--all fairly close to the long-term average.


Figure 1. Hurricane Alex approaching the Azores Islands in the far Eastern Atlantic on January 14, 2016. Alex peaked as a Category 1 storm with 85 mph winds on January 14, then weakened to a tropical storm with 70 mph winds when it made landfall on Terceira Island in the Azores on January 15. The storm caused minimal damage and was responsible for one indirect death. Alex was the first Atlantic hurricane in January since Alice in 1955, and the first to form in January since 1938. Image credit: NASA.

A boost from El Niño’s departure, but uncertainty about tropical Atlantic SSTs
The CSU forecast cited two main reasons why this may be a near-average hurricane season:

1) The El Niño event now drawing to a close in the eastern tropical Pacific is expected to transition toward neutral conditions this summer and La Niña conditions by autumn (see the discussion below). If La Niña conditions are present this fall, this would tend to favor a busier-than-usual Atlantic hurricane season due to a reduction in the upper-level winds over the tropical Atlantic that can tear storms apart. SSTs had fallen to 0.1°C below average over the past week in the so-called Niño3.4 region (5°S - 5°N, 120°W - 170°W), where SSTs must be at least 0.5°C above average for five consecutive months (each month being a 3-month average) for a weak El Niño event to be declared. This is the first below-average weekly value in the Niño3.4 area since July 2014. By August-October, most dynamical models are calling for either cool-neutral conditions (Niño3.4 anomalies between 0 and -0.5°C) or La Niña conditions (Niño3.4 anomalies of -0.5°C or greater). As summarized by CPC/IRI, the mid-May average of dynamical models was calling for a Niño3.4 value in August-October of -0.9°C. The European Centre for Medium-Range Weather Forecasts (ECMWF) shows the best prediction skill of the various El Niño/Southern Oscillation (ENSO) models, and the average of the various ECMWF ensemble members is calling for a Nino 3.4 SST anomaly of approximately -0.7°C for June-August, but rebounding slightly to -0.5°C by August-October, suggesting borderline-to-weak La Niña conditions. Several other models, including the NOAA Climate Forecast System (CFSv2), are projecting stronger La Niña conditions by the August-October period (the August-October anomaly from CFSv2 is -1.2°C, which would correspond to a moderate La Niña). In its monthly ENSO Diagnostic Discussion released on May 12, NOAA's Climate Prediction Center issued a La Niña Watch, with the new CPC/IRI probabilistic outlook calling for a 71% chance of La Niña during the August-October period.


Figure 2. Departures from average in sea surface temperature (in degrees C) during late May 2016. Image credit: CSU and NOAA/ESRL/PSD.


Figure 3. Departures from average in sea level pressure (in millibars/hPa) during May 2016. The Bermuda-Azores high was stronger than average, which was driving stronger trade winds than average over the tropical Atlantic. Image credit: CSU and NOAA/ESRL/PSD.

2) A fairly unusual sea-surface temperature pattern is present across the North Atlantic, leading to some uncertainty about how this factor will evolve later in the year. During 2016 to date, SSTs were above average in the Northwest Atlantic and below average in the far North Atlantic and eastern subtropical Atlantic, a pattern that the CSU group has associated with the negative phase of the Atlantic Multidecadal Oscillation. However, as shown in Figure 3 above, SSTs in the Main Development Region (MDR) for hurricanes, from the Caribbean to the coast of Africa between 10°N and 20°N, were slightly above average in late May (with the exception of cooler-than-average waters just off the coast of Africa). Virtually all African tropical waves originate in the MDR, and these tropical waves account for 85% of all Atlantic major hurricanes and 60% of all named storms. When SSTs in the MDR are much above average during hurricane season, a very active season typically results (if there is no El Niño event present.) Conversely, when MDR SSTs are cooler than average, a below-average Atlantic hurricane season is more likely. Despite the presence of above-average SSTs in the MDR this May, there is another factor that correlates even more strongly with the amount of Atlantic hurricane activity later in the year: the May SSTs across the eastern subtropical Atlantic and far North Atlantic. When these waters are cooler than average in springtime, as they are now, the CSU group finds that the cool SSTs tend to cause higher surface air pressure and stronger trade winds across the tropical Atlantic as the summer unfolds, which typically pushes the MDR SSTs below average by the peak of the Atlantic season.

While factor (1) suggests an above-average hurricane season, factor (2) would point toward a below-average season. Together with other variables considered in the CSU forecast, the result is the group’s projection of near-average conditions, which is similar to the NOAA outlook issued last week. See our post from May 27 for a roundup of the recent outlooks from NOAA and other groups, some of which are calling for more Atlantic activity than average. One factor in the mix: some long-range climate models are now projecting that slightly above-average SSTs will persist in the tropical Atlantic, as depicted in May output from the North American Multi-Model Ensemble.

As always, the CSU forecast included this standard disclaimer: “…coastal residents are reminded that it only takes one hurricane making landfall to make it an active season for them. They should prepare the same for every season, regardless of how much activity is predicted."


Figure 4. GOES satellite image of the remnants of Tropical Storm Bonnie at 1515Z (11:15 am EDT) Wednesday, June 1, 2016. Image credit: NASA Earth Science Office and NOAA.

Hurricane Hunters tasked to investigate ex-Bonnie
Satellite loops show that the remains of Tropical Storm Bonnie, located off the southeast coast of North Carolina on Wednesday morning, have increased in organization. Heavy thunderstorm activity has increased and the system has acquired more spin, thanks to the fact that ex-Bonnie is under a moderate 10 - 20 knots of wind shear and is over the relatively warm 26°C (79°F) waters of the Gulf Stream. The Hurricane Hunters have been tasked to investigate ex-Bonnie on Thursday afternoon as the storm heads slowly east-northeastwards out to sea at about 5 mph. Ex-Bonnie is expected to bring 1 - 2" of rain to extreme eastern North Carolina through Thursday. Wind shear is projected to remain light to moderate during the next 48 hours. Bonnie’s remnants will have an uphill battle fully regrouping, given that the system will remain fairly close to the Carolina coast until the shear rapidly increases by Friday, but the situation bears a close watch.

Where will the Atlantic's Tropical Storm Colin form?
The next named storm for the Atlantic will be named Colin, and there are two areas to watch next week for Colin's potential development. Over the Western Caribbean, a large area of low pressure laden with plenty of tropical moisture is expected to form early next week. This moisture will ride up over the Florida Keys and South Florida by Monday, bringing heavy rains of 2 - 4" through Tuesday. About 10% of the members of the ensemble runs of the 00Z Wednesday GFS and European models showed a tropical depression forming between the Western Caribbean and South Florida early next week, so we should keep an eye on this region. Wind shear will be high over the Central Gulf of Mexico, though, and this high shear will likely interfere with development. The other region to watch is the waters between Puerto Rico and Bermuda, where the GFS model predicts an area of low pressure capable of developing into a tropical cyclone will form on Sunday or Monday. This low would not be a threat to land, as prevailing winds would take it east-northeast away from the United States and the Caribbean.

First tropical depression of the season likely in the Eastern Pacific this week
In the Eastern Pacific, satellite loops show that an area of heavy thunderstorms located about 1000 miles south of the southern tip of the Baja Peninsula has become more concentrated over the past day. This disturbance (91E) is likely to develop into the Eastern Pacific's first tropical cyclone of the year late this week, according to recent runs of the GFS and European models. The disturbance is moving west-northwestward at about 15 mph, and is not a threat to any land areas. In their 8 am EDT Wednesday Tropical Weather Outlook, NHC gave 91E 2-day and 5-day odds of development of 50% and 90%, respectively. Should 91E become a tropical storm, it would be named Agatha. The first named storm of the year in the Eastern Pacific typically forms on June 10, so we would be very close to climatology if Agatha were to develop later this week.


Jeff Masters and Bob Henson

Hurricane


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

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