Category 6™

Tropical Atlantic Quiet; Pacific Getting Active

By: Jeff Masters , 3:21 PM GMT on June 30, 2015

The tropics are quiet in the Atlantic Ocean, where no tropical storm activity is likely for at least the next week. A moderate-strength El Niño event is underway in the Eastern Pacific, and the atmospheric circulation associated with the strong warming of the waters off the coast of Peru is creating strong upper-level winds over the Caribbean. These powerful winds were creating a very high 60 - 70 knots of wind shear over the Caribbean and Southern Gulf of Mexico on Tuesday, making tropical storm formation virtually impossible in these regions. In addition, the atmosphere over the tropical Atlantic, including the Caribbean Sea, has been dominated by high pressure and dry, sinking air since April, which has made it difficult for thunderstorms to develop. The high wind shear and low instability is forecast to persist in the Caribbean and tropical Atlantic for at least the next week. Wind shear is lower in the waters of the Gulf of Mexico and off the U.S. East Coast, so if we get any tropical storms forming during the first week of July, those would be the most likely locations. Tropical storms that form just off the U.S. coast typically get going along a cold front that moves off the coast and then stalls over the water. The models are currently showing no fronts active enough to promote such development through the first week of July.

Figure 1. Vertical instability over the Caribbean Sea in 2015. The instability is plotted in °C, as a difference in temperature from near the surface to the upper atmosphere. Thunderstorms grow much more readily when vertical instability is high. Normal instability is the black line, and this year's instability levels are in blue. The atmosphere has been dominated by high pressure and dry, sinking air since April, which has made it difficult for thunderstorms to develop. Instability has also been unusually low in the tropical Atlantic between the Lesser Antilles Islands and coast of Africa, but has been near average over the Gulf of Mexico and waters off the U.S. East Coast. Image credit: NOAA/CIRA.

Rare twin tropical cyclones form in the Pacific
The Madden Julian Oscillation (MJO), a pattern of increased thunderstorm activity near the Equator that moves around the globe in 30 - 60 days, is currently located in the Western Pacific, and is forecast to grow to impressive strength by this weekend. In response to the MJO and the unusually warm waters from the current El Niño event, heavy thunderstorm activity is firing up along a large swath of the tropical Western Pacific Ocean, along what is called the "Monsoon Trough". On Tuesday morning, this activity spawned twin tropical cyclones just west of the Date Line, one storm on either side of the Equator. The Northern Hemisphere storm is Tropical Depression Chan-hom, which is likely to intensify into a typhoon this weekend and track northwest through the Northern Mariana Islands, north of Guam. Chan-hom is the ninth named storm in this very busy Northwest Pacific typhoon season. According to statistics from the Japan Meteorological Agency at Digital Typhoon, only two seasons since 1950 have had more named storms by the end of June--1971 (with 11) and 1965 (with 10.) The Southern Hemisphere twin storm is Tropical Cyclone Twenty-five, which is expected to slowly intensify and move southwards through the Solomon Islands. It is very rare to get a tropical cyclone in this portion of the South Pacific in late June and early July--winter in the Southern Hemisphere. According to statistics from NOAA's historical hurricane website, there have been only three July named storms in the waters of the South Pacific east of Australia since satellite data began in 1970. None of the these storms occurred in the waters north of the Solomon Islands, where Tropical Cyclone Twenty-five formed.

Figure 2. Surface wind flow over the equatorial Pacific as seen at 10 am EDT June 30, 2015. A series of four counter-clockwise rotating tropical disturbances (one of them being Tropical Depression Chan-hom) was in the Northern Hemisphere, and one tropical depression (Twenty-five) was in the Southern Hemisphere. Image credit:

Twin tropical cyclones will aid El Niño
The counterclockwise flow around Tropical Depression Chan-hom in combination with the clockwise flow around Tropical Cyclone Twenty-five is generating a Westerly Wind Burst (WWB) near the equator, just west of the Date Line. The winds of this WWB are predicted to march eastwards towards South America during the coming weeks, pushing more warm water eastwards that will reinforce the on-going moderate-strength El Niño event. This El Niño event is already at the borderline of being categorized as "strong", and this new WWB could well push it past that threshold. This should make for an unusually active Eastern Pacific hurricane season, by bringing warmer waters and lower wind shear (next chance for a named storm there: in about ten days' time, when the MJO pushes eastwards into the Eastern Pacific.) Conversely, El Niño should bring a much less active than usual Atlantic hurricane season, thanks to the high levels of wind shear that typically occur there during an El Niño.

Jeff Masters


Unprecedented June Heat in Northwest U.S. Caused by Extreme Jet Stream Pattern

By: Jeff Masters , 2:30 PM GMT on June 29, 2015

A searing heat wave unprecedented for June scorched the Northwest U.S. and Western Canada on Saturday and Sunday. Temperatures soared to their highest June levels in recorded history for portions of Washington, Idaho, Montana, and British Columbia; both Idaho and Washington set all-time high temperature records for the month of June on Sunday. According to wunderground's weather historian, Christopher C. Burt, the 113°F measured in Walla Walla, Washington beat that state's previous June record of 112°F, set at John Day Dam on June 18, 1961. In addition, the 111°F reading at Lewiston, Idaho was that state's hottest June temperature on record. An automated station at Pittsburg Landing, Idaho hit 116°F, but that reading will have to be verified before being considered official. A slew of major stations set all-time June heat records on both Saturday and Sunday in Washington, Idaho, and Montana, and at least two tied their hottest temperature for any day in recorded history. A destructive wildfire hit Wenatchee, Washington overnight, destroying twelve buildings. Wenatchee set a new June record high of 109°F on Sunday, just one degree shy of their all-time record of 110°F set on July 17-18, 1941. Jon Erdman of TWC has full details of all the records set. Sunday will end up being the hottest day of the heat wave for most locations in the Northwest U.S. and Western Canada, but temperatures will still be 10 - 15°F above average most of the remainder of the week.

Figure 1. A wildfire burns in Wenatchee, Washington on Sunday, June 28, during the hottest June temperatures ever recorded there. Image credit:

What caused the heat wave?
The planet as a whole has experienced its warmest January - May period on record this year, and it is much easier to set all-time heat records when your baseline temperature is at record warm levels. But all-time records require some unusual meteorology, and this week's heat wave was caused by an extreme jet stream configuration that featured a very sharp ridge of high pressure over Western North America and a compensating deep trough of low pressure over the Midwest United States. The ridge of high pressure allowed hot air from the Southwest U.S. to push northwards, and brought sunny skies that allowed plenty of solar heating of the ground. An extreme jet stream configuration also was in evidence over Western Europe, where a strong ridge of high pressure on Sunday brought the warmest June temperatures ever recorded to the Spanish cities of Madrid and Toledo. This sort of extreme jet stream pattern has grown increasingly common in recent decades, as I wrote about for the December 2014 issue of Scientific American (behind a pay wall for $6.) A study published last week by researchers at Stanford University found that unusually intense and long-lived high pressure systems of the kind responsible for heat waves have increased over some parts of the globe since the advent of good satellite data in 1979. In particular, they found that in summertime, these patterns had increased over Europe, western Asia, and eastern North America. As yet, scientists have not come to a consensus on what might be causing the jet stream to behave in such an extreme fashion, though one leading theory is that rapid warming of the Arctic that has led to record sea ice and spring snow cover loss might be responsible.

Figure 2. Departure of temperature from average at 2 meters (6.6') as diagnosed by the GFS model at 00 UTC June 28, 2015. A sharp kink in the jet stream (Figure 3) allowed warm air to flow northwards into the Northwest U.S. and Western Canada beneath a ridge of high pressure, bringing temperatures up to 20°F above average. A compensating trough of low pressure set up over the Midwest U.S., allowing cold air to spill southwards and cause an usually cool June day. Data/image obtained using Climate Reanalyzer™ (, Climate Change Institute, University of Maine, Orono, Maine.

Figure 3. Winds at a height where the pressure is 250 mb show the axis of the jet stream, seen here at 00 UTC June 28, 2015. An unusually strong ridge of high pressure was over Western North America and Western Europe, leading to all-time June temperature records being broken in both places. Data/image obtained using Climate Reanalyzer™ (, Climate Change Institute, University of Maine, Orono, Maine.

A few of my recent posts discussing extreme jet stream behavior
Buffalo Belted With Five Feet of Snow; Is Jet Stream Weirdness to Blame? my November 2014 post.
California Drought/Polar Vortex Jet Stream Pattern Linked to Global Warming, my April 2014 post.
Extreme Jet Stream Bringing U.S. Record Heat, Record Cold, and Flash Flooding, my July 2013 post.
Extreme Jet Stream Pattern Triggers Historic European Floods, my June 2013 post.
Are atmospheric flow patterns favorable for summer extreme weather increasing? my March 2013 post.
Where's spring? 2nd most extreme March jet stream pattern on record extends winter, my March 2013 post.
Extreme jet stream causing record warmth in the east, record cold in the west, my January 2013 post.
Arctic sea ice loss tied to unusual jet stream patterns, my April 2012 post.
Summer in March, 2012, draws to a close, my March 2012 post.
Our extreme weather: Arctic changes to blame? my December 2011 post.

Note: I originally posted that Cranbrook, British Columbia hit 98°F (36.8˚C), its hottest temperature of any day since records began in 1901. Weather Records researcher Maximiliano Herrera pointed out to me that Cranbrook has changed location 4 times, and has had five reporting stations. If we consider all of these locations, Sunday's 36.8˚C reading does not set a record. Here are the highest temperatures at the main Cranbrook station:

37.2˚C 7/18/1918
37.8˚C 7/4/1924
38.3˚C 7/12/1940
38.9˚C 7/16 and 7/17 1941
37.8˚C 7/27/1939
37.8˚C 7/12/1953
37.2˚C 8/17 and 8/18 1967

Jeff Masters

Heat Extreme Weather

PECAN: Closest Look Yet at Nighttime Storms That Pummel Midwest

By: Bob Henson , 8:17 PM GMT on June 26, 2015

In most parts of the country, summer thunderstorms are most common in the afternoon or evening. Things are a bit different from the eastern Great Plains into the western Great Lakes. Across this core swath of the Midwest, lightning is most likely to zigzag across the summer sky during the wee hours of the morning. Along with disrupting countless nights of sleep, these middle-of-the-night thunderstorms are renowned for torrential rain, large hail, and destructive wind. One of several vivid examples from the past week was the supercell that moved across western South Dakota on Friday night, June 19, killing livestock with softball-sized hail before morphing into an larger complex that sent wind gusts of 60 to 100 mph across the southern half of the state well past midnight, finally reaching southwest Minnesota around 3:00 a.m. See radar loop here (also embedded at the bottom of this post).

Figure 1. A powerful supercell, shown here near Belle Fourche, SD, raced across South Dakota on Friday night, June 19, while evolving into a mesoscale convective system (MCS). Image credit: Cody Lere, courtesy of NWS Rapid City.

This year a major field study--primiarly supported by the National Science Foundation, with additional support from NASA, NOAA, and DOE--is zeroing in on large, long-lived storm clusters known as mesoscale convective systems (MCSs) as they prowl the central Plains from late evening deep into the night. The experiment, dubbed Plains Elevated Convection at Night (PECAN), started on June 1 and will continue through July 15 if the weather remains favorable. PECAN is a sprawling Kansas-based project, with an operations center at Fort Hays State University, three aircraft (a University of Wyoming King Air, NOAA P-3, and NASA DC-8), and a fleet of mobile teams, including nine portable Doppler radars and four vertical profiling units (PECAN Integrated Sounding Arrays, or PISAs). Six other PISAs are based at fixed sites. The project’s official domain extends from northern Oklahoma to southern Nebraska, although the P-3 flew into South Dakota to investigate the storm of June 19 and a successful mission took place in Iowa on Wednesday night, June 24.

PECAN’s overarching goal is to “advance the understanding and forecast skill of the processes that initiate and maintain nocturnal convection in the Great Plains.” It’s no mystery that nighttime MCSs are a huge influence on central U.S. climate. Roughly half of the summertime rainfall over the Great Plains is deposited by MCSs. Often, the systems develop night after night along a preferred west-to-east corridor whose location can shift north or south in a given year. Most nighttime MCSs over the plains are elevated, meaning they draw energy from just above the lowest few thousand feet of the atmosphere (the boundary layer). As the sun goes down, the boundary layer cools more quickly than the air above it, which can lead to an often-sharp inversion that keeps the two layers separated. Above the boundary layer, storm-fueling warmth and moisture from the Gulf of Mexico can sweep unimpeded into MCSs, borne on a southerly low-level jet stream that routinely ramps up around nightfall. Winds in this low-level jet stream often top 60 mph, which can keep an MCS going for hours on end. Some MCSs can persist for more than 12 hours and travel more than 1,000 miles.

Figure 2. Radar data from WSI, covering the June-to-August periods from 1996 to 2002, was used to produce this climatology that shows the time of day when precipitation (inferred from radar reflectivities of more than 15 dBz) were most likely. Much or most of this rain would be in the form of thunderstorms. Areas in black and dark blue/purple denote peak activity between around midnight and 6:00 a.m. local solar time. Image credit: David Ahijevych, NCAR.

Some weather patterns are reliable MCS producers, making a given night’s forecast fairly straightforward. Other setups are more ambiguous, leading to the risk of unpleasant, dangerous surprises in the middle of the night. “In some cases it's clear that the MCS will move in a certain direction, but the forecasters may struggle with how long it will last,” said Mike Coniglio (NOAA National Severe Storms Laboratory), one of the PECAN co-investigators. “Other times the MCS motion can be quite a forecast challenge, since it depends on both the fine-scale details of the cold air produced by the cluster of thunderstorms as well as the details of the vertical wind profile surrounding the system, which itself often changes drastically in the few hours after sunset.” Still other times, an MCS will stay potent well through the night, producing severe weather and even tornadoes, despite background conditions that suggest a stable layer near the ground would inhibit the severe weather.

Figure 3. On June 4, NCAR’s S-Pol research radar monitored this rapidly developing thunderstorm in western Kansas, which merged with other cells as part of an MCS after sunset. S-Pol is stationed southwest of Hays for the PECAN project. Image credit: Carlye Calvin/UCAR.

To address the forecast question from several angles, PECAN is oriented around four distinct mission types. Each night of operations will include one or more sub-experiments organized around these four areas:

--The birth and early life of elevated storms: How do various types of disturbances kick off thunderstorms in the late evening, as the boundary layer is just beginning to detach from the atmosphere above it?

--The internal structure and microphysics of MCSs: How do the rain-cooled downdrafts from MCSs affect storm evolution? How well does the new dual-polarization software in NWS NEXRAD radars classify the size and types of raindrops, ice crystals, and cloud droplets found in MCSs?

--Bores and other wave-like features: MCSs can trigger atmospheric features that propagate well beyond the storm complex itself. One such feature that’s not well known to the public is the undular bore, which ripples outward against the prevailing wind much like a tidal bore does. These wavelike features can help nourish an MCS by forcing downstream air above the boundary layer to rise. What drives these features, and how can they be better folded into prediction efforts?

--Storm- and MCS-scale modeling: Data gathered from the field in PECAN will be teamed with computer models at various resolutions, to analyze what types of future observation platforms might be best suited for improving forecasts of MCS evolution. According to Coniglio, current storm-scale models tends to produce downdrafts that are too cold and spread out too extensively, which makes it harder to predict MCS behavior.

Figure 4. Undergraduates Leslie Cain (Fort Hays State University) and Shiou-Rong Chu (National Taiwan University) calibrated and launched radiosondes for PECAN from a fixed monitoring site near Brewster, Kansas. Image credit: Carlye Calvin/UCAR.

Life on the graveyard shift
This spring’s thunderstorm action shifted rather abruptly from torrential rain-producing storms in Oklahoma during May to MCSs swinging across the upper Midwest in June. Although Kansas hasn’t been the prime focal point of MCS development, enough storms have been moving through the northern part of the PECAN domain to keep the researchers busy, and the aircraft component extends the project range somewhat. PECAN is budgeted for up to 27 observing periods, and Thursday night was the 16th night of operations, with about three weeks left to go.

PECAN’s unusual hours are well suited for undergraduate and graduate students who know all about pulling all-nighters. Several dozen students have been launching radiosondes and deploying other equipment as part of PECAN’s mobile teams. Unlike chase-oriented projects such as VORTEX2, where mobile units move with storms throughout the afternoon and evening, PECAN’s mobile units generally stay put after their late-evening deployment. Once data gathering is done for the night, which can be as late as 3:00 or 4:00 am, it’s time to catch a few winks before gearing up in time for the next day’s 3:00 pm weather briefing. “Some of us have resorted to putting aluminum foil over the bedroom windows to block out the morning light and try to get on a roughly 3-am-to-11-am sleep schedule,” said Coniglio.

Figure 5. The PECAN PIE group, one of the teams of students and scientists documenting storms across the central Great Plains for weeks on end as part of PECAN. Left to right: Anthony Torres (University of Michigan), Erin Dougherty (2015 graduate, University of Virginia), and postdoctoral fellows David Bodine and Kristen Rasmussen (NCAR Advanced Study Program).

“I’ve just been pretending I'm in another time zone,” said Anthony Torres (University of Michigan), an undergraduate taking part in PECAN through UCAR’s SOARS program. “It's been a challenge remembering what day it is, what's considered breakfast, lunch, dinner, etc.” Torres and several other participants have dubbed themselves PECAN PIE, with the PIE standing for Precipitation Instrumentation Experiment. On Thursday night, they were in the midst of a multi-day deployment ranging across several states, using instruments called disdrometers that measure the sizes and fall speeds of individual raindrops. The PECAN PIE team has set up a Facebook page and their own WU blog, which they’ll soon be updating.

“We always see something interesting in the data,” says Tammy Weckwerth, one of six PECAN principal investigators. “It may be the structure and evolution of the MCSs, or the organization of the convection initiation events, or seemingly endless bores emanating out from storms, or interesting surface boundaries, or mid-level moisture tongues, or widespread waves propagating throughout the region. No matter when we collect data or what the conditions are, there is always something intriguing going on in the atmosphere.”

The PECAN Field Catalog, maintained by NCAR’s Earth Observing Laboratory, includes many links to outreach-oriented material. See also the NSF and NCAR news releases on PECAN and Jon Erdman’s comprehensive writeup on MCSs and PECAN at Thanks to Jon for providing additional background for this blog post.

Bob Henson

Severe Weather

Big Contrasts this Weekend: Roasting Out West, Soaking Back East

By: Bob Henson , 3:15 PM GMT on June 25, 2015

The atmosphere over North America will slide back into a familiar pattern this weekend, as a powerful upper ridge and record heat take hold of the Pacific Northwest and western Canada while an unusually strong upper low for late June brings wet, cool conditions from the Ohio Valley through the mid-Atlantic into New England. It’s yet another variation on the warm-west/cool-east pattern that predominated through much of 2014 and early 2015.

Sizzling temps on tap for Pacific Northwest
While it’s been an unusually hot, muggy June across much of the Southeast, the burners will soon be going full blast out West. Models are consistent in building strong high pressure across the western states late this week into next week. The results will be scorching temperatures, especially in parts of eastern Washington and Oregon where warm, dry weather in recent weeks has left the ground already parched. Highs are projected to range from 100°F to 110°F over most of the next 4 to 6 days across a large area. Excessive heat watches are in effect for both Portland and Seattle. Here are some of WU’s forecast highs compared to monthly and all-time records. (For more, see the roundup by Jon Erdman at

—Spokane, WA: Forecast high 102°F (Sunday); All-time record is 108 degrees on July 26, 1928 and Aug. 4, 1961
—Boise, ID: Forecast high 106°F (Sunday); All-time record is 111 degrees on July 19, 1960 and July 12, 1898
—Salt Lake City, UT: Forecast high 103°F (Monday); June record is 105 degrees on June 28-29, 2013
—Portland, OR: Forecast high 99°F (Saturday); June record high is 102 degrees on June 26, 2006
—Reno, NV: Forecast high 102°F (Friday and Saturday); June record is 104 degrees on June 16, 1940
—Missoula, MT: Forecast high 102°F (Sunday and Monday); June record high is 100 degrees on Jun. 29, 1937 and Jun. 13, 1918.

The heat may abate slightly by the middle of next week over the Pacific Northwest, but longer-range models suggest unusual warmth continuing across much of Canada. There are also hints that a significant heat wave could develop over parts of Europe toward the latter part of next week and beyond, as a highly amplified jet-stream pattern sets up there. The WU extended forecast brings Paris into the mid-90s Fahrenheit for several days, starting next Wednesday.

Figure 1. Temperatures will be 10°F to 30°F above average across large parts of the western United States and Canada, while much of the eastern U.S. will be unusually cool, according to the forecast for 0000 GMT Tuesday, June 30, produced by the 1800 GMT Wednesday run of the GFS model. Image credit: Climate Reanalyzer/University of Maine.

Fire risk increasing over western U.S., Alaska
By recent standards, it’s been a relatively quiet year thus far for wildland fire across the United States. The total amount of land affected by fire through Tuesday, June 23, stands at 885,842 acres, according to the National Interagency Fire Center. That’s slightly above last year’s total through June 23, but well below each of the years from 2005 to 2013. The threat of wildfires should begin ramping up this weekend, though, with record heat and dry lightning storms over parts of California, Oregon, and Washington, as well as western Canada and Alaska. On Wednesday afternoon, more than 1,000 people had to flee a fast-growing 350-acre wildfire near Interstate 5 in Santa Clarita, CA, just north of the San Fernando Valley.

Figure 2. Smoke from the Washington Fire rises over the Sierra Nevada range south of Lake Tahoe as viewed from between Minden and Carson City, NV, on Monday, June 22. The wildfire had grown to over 20 square miles in hazardous and inaccessible terrain and was moving closer to structures, officials said. The Lake Tahoe area saw record-low amounts of snowpack this past winter. Image credit: Jim Grant/ Nevada Appeal via AP.

The greatest fire risk this weekend will be around the edge of the strong high pressure cell taking shape over the interior West. In and near the Cascades, enough moisture should be present for scattered thunderstorms with little rain but gusty winds and lightning. Combined with very hot weather and dry vegetation, this is among the most dangerous scenarios for wildfire risk. Lightning is the main cause of wildfires in the Pacific Northwest, according to Cliff Mass (University of Washington), who outlines the upcoming risk in detail in a blog post. “The bottom line is that with very dry conditions in place, multiple lightning-caused fires are quite possible. Fire folks need to get ready,” said Mass. The fire danger is also high to extreme over much of western British Columbia. The NOAA Storm Prediction Center has not yet outlined any high-probability areas in its 3-8 day fire weather outlook, but the discussion issued Wednesday afternoon notes the possibility of an upgrade as the time period draws closer and confidence in model solutions increases.

Figure 3. Smoke cloaks the skies above Fort Wainwright, Alaska, near Fairbanks, on Wednesday. The smoke is a byproduct of several large wildland fires burning in central Alaska. Image credit: Stephanie Frank.

Most of the major U.S. fires this year to date have been in Alaska, where sporadic bursts of record heat during the spring and early summer have dried out vast stands of forest and brushland. Eleven fires affecting more than 1000 acres each were in progress as of Wednesday, with six of those exceeding 10,000 acres. Several factors are pushing Alaska toward longer and more intense fire seasons, as outlined by Climate Central in a report published Wednesday. The state is warming twice as quickly as the U.S. average--almost 3°F since the 1950s—and the average fire season has lengthened by roughly 40 percent in the last 60 years. Hot temperatures from May to July are strongly related to the frequency and severity of fire seasons in Alaska.

Large fires (more than 1000 acres) have grown far more common in the tundra-dominated Arctic portion of Alaska: such fires occurred in only three years from 1950 through 1969, but 33 such fires have struck the Alaskan Arctic since 2000. “We’re starting to see a tundra-fire regime emerging within the past few decades,” said Todd Sanford (CIRES), the lead author of the report. Earth’s largest tundra fire on record occurred in 2007, when about 250,000 acres (380 square miles) were scorched in the vicinity of the North Slope’s Anaktuvuk River. Such a lightning-triggered fire was once virtually impossible on the damp, chilly tundra. Lake sediments from the region around the Anaktuvuk fire showed no evidence of any other major fires in the last 5,000 years. Further south, wildfire is paving the way for an infusion of deciduous trees into the evergreen forests of the Alaskan interior. According to the 2014 U.S. National Climate Assessment, “More extensive and severe wildfires could shift the forests of Interior Alaska during this century from dominance by spruce to broadleaf trees for the first time in the past 4,000 to 6,000 years.”

A stormy week for Midwest, mid-Atlantic
A strong polar jet stream from the Corn Belt to the East Coast has been ferrying intense thunderstorms from west to east all week. Tuesday brought one of the biggest severe weather outbreaks of 2015, with severe storms sweeping through the mid-Atlantic corridor into New England. At the peak of the storms, some 770,000 people were without power, and widespread tree damage was reported.

Figure 4. A huge mesoscale convective complex (MCS) sprawls across the upper Midwest in this infrared satellite image taken at 8:15 a.m. CDT on Monday, June 22. The pink shadings over northern Iowa and southeast Minnesota correspond to the highest cloud tops associated with the most vigorous thunderstorms. Image credit:

Figure 5. Tornado paths and strengths across northeast Illinois on Monday evening, June 22. Image credit: NWS Chicago.

One of the most powerful storms pushed through southeast Pennsylvania into southwest New Jersey, where power outages exceeded those from Superstorm Sandy and the 2012 derecho. Winds gusted to 85 mph in Gloucester County, NJ, and to 72 mph at Philadelphia International Airport, just a few weeks after outflow from a weak shower on April 22 brought 71-mph winds. The city has recorded gusts that strong only four other times in its weather history.

The day before the mid-Atlantic got slammed, Monday brought a preliminary total of 19 tornadoes, with 9 of them from a long-lived supercell that carved a path just southwest of Chicago (see Figure 5). A long-track, high-end EF3 twister that struck near Coal City was the strongest observed in the Chicago metro area since the deadly F5 Plainfield tornado of August 28, 1990. Another EF3 was reported near Marysville, Iowa. At, Jon Erdman produced this assortment of eye-popping imagery from Monday’s and Tuesday’s storms.

Figure 6. Gary Rink walks behind his home on Tuesday, June 23, in Coal City, Ill., after a tornado passed through the area Monday evening. The community of about 5,000 residents is located about 60 miles southwest of Chicago. Image credit: AP Photo/Charles Rex Arbogast.

Wet weekend on tap for Northeast
Though at least it’s arriving a week before the Fourth of July holiday, a rainy, cool storm system will likely put a big damper on outdoor activities this weekend from the Ohio Valley into the mid-Atlantic and New England. The west-to-east jet stream that’s powered storms all week will buckle into a pronounced upper-level low that will move slowly across the region. A double-barreled surface low may develop, similar to the configuration seen in many nor’easters. Cool temperatures should tilt the odds away from thunderstorms toward steady rain over the coastal cities, where 1” to 3” of rain possible. Heavier downpours could fall over the upper Ohio Valley and Appalachians. With 9.57” reported this month through Wednesday, Baltimore has already landed the second-wettest June in its 145 years of weather history. The record of 9.95”, set in June 1972, could be eclipsed by an inch or more before the month is out.

Bob Henson

Figure 7. Projected three-day precipitation totals from the NOAA Weather Prediction Center, for the period from 1200 GMT June 25 to June 30. Image credit: NWS/WPC.

Figure 8.. The setting sun illuminates mammatus clouds over Pottsgrove, PA, in the wake of Tuesday’s severe storms. Image credit: wunderphotographer Jerry1481.

Heat Extreme Extreme Weather Fire

Pakistan's Deadliest Heat Wave on Record Kills at Least 800

By: Jeff Masters , 5:37 PM GMT on June 24, 2015

The death toll from a brutal heat wave in Pakistan rose to 830 on Wednesday, making it Pakistan's deadliest heat wave in recorded history. Most of these deaths--at least 770--occurred in Pakistan's largest city, Karachi. According to statistics from EM-DAT, the International Disaster Database, Pakistan's previous deadliest heat wave was in 1991, when 523 people died.

Death Tolls from the 5 Deadliest Heat Waves in Pakistan's History
1) 2015: 830+
2) 1991: 523
3) 2014: 248
4) 2003: 200
5) 1953: 111

Figure 1. Pakistanis receive ice outside a hospital during heatwave in Karachi on June 24, 2015. A state of emergency was declared in hospitals. Image credit : RIZWAN TABASSUM/AFP/Getty Images.

Figure 2. Temperatures in Karachi, Pakistan from June 11 - June 24, 2015 show that the heat wave peaked on June 20, with a high temperature of 112.6°F (44.8°C.) The heat index was as high as 121°F.

The worst of the heat is over for Pakistan
The past week saw an unusually long string of very hot days with temperatures that did not cool off at night in Pakistan. The heat wave peaked on Saturday June 20, when the high temperature hit 112.6°F (44.8°C) in Karachi; the heat index peaked at a dangerously high 121°F. According to the Pakistan Meteorology Department, Karachi's all-time high temperature was 118°F (47.8°C) on May 9, 1938. A tropical depression associated with the approaching southwest monsoon pushed ashore along the border of Pakistan and India on Tuesday, bringing thunderstorms and cooler weather. Wednesday's high reached only 98°F in Karachi, breaking a streak of six consecutive days when the temperature hit 103°F or higher. The previous longest streak of 103°F+ temperatures during the past fifteen years was three consecutive days, which occurred most recently in 2006. Temperatures failed to dip below 85°F at night during the streak of 103°F days over the past week; very warm nights are associated with high mortality during intense heat waves, since there is no chance for the body to gain an overnight respite. High temperatures are expected to rise to 103°F again in Karachi on Thursday, but then cool to the upper 90s over the weekend--about ten degrees Fahrenheit cooler than last weekend's temperatures. The cooling rains from the southwest monsoon are likely to arrive in Karachi by mid-July, and the circulation associated with the monsoon should insure that the region will not see any more temperatures this summer as high as were recorded last weekend. If the death toll from the 2015 Pakistan heat wave rises above 1,030, it will join this year's May 2015 heat wave in India as one of the ten deadliest heat waves in world history.

Figure 3. Progress of the monsoon towards Pakistan as of June 23, 2015 (green line) has been about a week slower than its usual pace. Karachi, Pakistan usually sees the monsoon move through during the second week of July. Image credit: India Meteorological Department .

A deficient monsoon predicted, but above-average rains so far
The atmospheric circulation patterns brought on by an El Niño event usually cause much reduced monsoon rains in India. With the current moderate El Niño event is forecast to intensify this summer, the India Meteorological Department (IMD) is forecasting only a 7% chance of near-average rains during the 2015 summer monsoon period, and a 93% chance of below average or well below average rains. IMD's best estimate is that 12% less rain than usual will fall. However, during the first half of June, monsoon rainfall was 11% above average for India as a whole.

Climate change and the monsoon
This year's deadly heat waves in India and Pakistan were made much more probable by the fact that Earth is experiencing its hottest temperatures on record--the January - May 2015 period was the planet's hottest such period on record. The planet's record heat contributed to unusually warm ocean temperatures off the coast of Pakistan, which were about 1°C (1.8°F) above average this week. Warmer oceans make hotter heat waves over adjoining land areas more likely. According to the India Meteorological Department, a warming climate increased heat waves in India by a third between 1961 to 2010. As the planet continues to warm due to human-caused global warming, heat waves will become more frequent and more intense, and heat-related deaths will soar unless we take strong measures to adapt. An April 2015 paper published in Regional Environmental Change, Intensification of future severe heat waves in India and their effect on heat stress and mortality, warned that "heat waves are projected to be more intense, have longer durations and occur at a higher frequency and earlier in the year. Southern India, currently not influenced by heat waves, is expected to be severely affected by the end of the twenty-first century." Perhaps a bigger concern for India and Pakistan with climate change is drought, though. Many climate models show that climate change might increase the average rainfall in India and Pakistan from the monsoon, but when dry years occur, the hotter temperatures accompanying the dry years will drive much more intense droughts capable of causing significant challenges to growing food.

Jeff Masters

Heat Climate Change

A New Take on the Human Factor in Recent Extreme Events

By: Jeff Masters and Bob Henson , 3:17 PM GMT on June 23, 2015

Much debate in the last few years has centered on persistent kinks in the polar jet stream and the extreme weather they’ve helped produce, such as the record snowfalls in New England last February. Top researchers differ on how much a changing climate might be involved with this jet-stream “weirding.” However, there’s no question that sea levels have risen and global temperatures have warmed. Those unassailable facts may serve as the most direct link between climate change and extreme events, according to the Perspectives article Attribution of climate extreme events, published on Monday in Nature Climate Change. The authors include Kevin Trenberth and John Fasullo (National Center for Atmospheric Research) and Theodore Shepherd (University of Reading, England).

Trenberth is a leading expert in the global flows of energy and water around the world. Because warmer temperatures and increased water vapor have influenced the whole of Earth’s atmosphere, Trenberth and colleagues start with the premise that every storm is influenced by climate change to at least some extent. “The environment in which all weather events occur is not what he used to be,” their new paper states. At the same time, they agree that no storm is entirely a result of climate change: “ is not possible to attribute a single climate extreme event, which by definition is unique and which has a large element of chance in its occurrence, to a specific cause.”

Figure 1. Temperature anomalies for July 2003 in western Europe, as calculated by observations from NASA’s Terra satellite. Image credit: Reto Stockli and Robert Simmon, based upon data provided by the MODIS Land Science Team.

Recognizing this quandary, many researchers who look into climate change and extreme events use models and observations to gauge how much of the risk of a particular extreme can be attributed to a warming planet. A landmark study led by Peter Stott (UK Hadley Centre) found a greater-than-90-percent chance that a European heat wave on par with the 2003 disaster that killed an estimated 70,000 people had become at least twice as likely due to human-produced greenhouse gases. Such studies often call on large-scale circulation, such as the flow at 500 millibars, as a key index of the extreme event. But there is a great deal of natural variability in where upper-level highs and lows set up, so an attribution study focused on circulation might find no evidence that climate change helped create a extreme event, even if there is unprecedented rainfall or heat--the variables that actually cause impact--associated with it. The new paper suggests that a more useful question might be: “Given the weather pattern, how were the temperatures, precipitation and associated impacts influenced by climate change?” The paper goes on to look at four recent events (see below) and how they would look through this lens.

Dáithí Stone, an attribution expert at Lawrence Berkeley National Laboratory and leader of the Weather Risk Attribution Forecast, sent me this take on the paper: "Recent studies exploring the role of greenhouse gas emissions in extreme weather events tend to be conservative by working under the 'innocent until proven guilty' paradigm, but this paper argues it would also be useful to work under the 'guilty until proven innocent' paradigm, or something in between. This is really the precautionary principle and can certainly make sense for adaptation decisions: even though residents of a coastal city might not have been measuring sea level, they may still think it wise to assume it is rising. But looking at things in the innocent-until-proven-guilty approach can be wise too, as in the Western legal systems designed to prevent witch hunts. So which paradigm is better depends on the purpose."

It remains to be seen which scientists will follow the lead of the new paper and focus more on thermodynamics (heat, moisture) and sea level rise, as opposed to circulation change. Jennifer Francis (Rutgers University) is among those who’ve found evidence for a link between depleted Arctic sea ice and unusual jet-stream behavior. In an email to me, she agreed with the overall conclusion of Trenberth and colleagues: “One should focus on climate changes that are irrefutable--such as rising sea levels, warmer tropospheric temperatures, increased water vapor, warmer SSTs, and changing soil moisture--all on a case-specific basis. Given a particular circulation pattern or weather system, these changes will affect the impacts of that system.” At the same time, she maintains that the question of how cutoff lows, blocking highs, and other jet-stream configurations may be changing is equally important. “Addressing this question requires a different approach that identifies and measures changes in these types of patterns,” said Francis. “For example, knowing whether the frequency of strong ridging in the eastern Pacific will change depending on certain factors--such as Pacific sea-surface temperature (SST) patterns and/or Arctic sea-ice loss--will be tremendously valuable in planning for water resources in western states.” She added: “Changes in dynamics are harder to pin down, but ultimately they have a farther-reaching impact on probabilities of particular extremes.”

Below are summaries of the four events linked by Trenberth and colleagues to thermodynamic and sea-level changes. The full paper can be viewed from a link at this Guardian blog post by John Abraham, thanks to a content sharing initiative. At Mashable, Andrew Freedman provides additional perspective on the new paper. A matrix created in 2012 for UCAR/NCAR AtmosNews outlines several different ways that scientists have approached the attribution of extreme events to climate change.

Jeff Masters and Bob Henson

Figure 1. Hurricane Sandy at 10:10 am EDT October 28, 2012. Image credit: NASA/GSFC.

1) Hurricane Sandy, 2012
Hurricane Sandy, the most powerful and second most destructive Atlantic hurricane in recorded history, barreled into New Jersey on October 29, 2012, bringing hurricane-force winds, torrential rains, heavy snow, and a massive storm surge. Sandy's catastrophic storm surge was responsible for the majority of the storm’s 131 deaths and $62 billion in damage in the United States. While papers have been published arguing that climate change could be expected to make Sandy’s unusual 1-in-700 year track west-northwestwards into new Jersey more or less likely, the authors of Monday’s study argue that the increased sea surface temperatures (SSTs) along its track due to global warming likely led to a bigger, more intense storm, stronger winds, and greater precipitation. Sandy traversed a broad strip of SSTs that were 1 - 1.5 °C warmer than average along the U.S. East Coast, and a 2014 model study using the European model by Magnusson et al., Evaluation of medium-range forecasts for Hurricane Sandy, found that these warmer SSTs decreased Sandy’s central pressure by 7.6 mb, increased the winds by 8 mph (3.6 m/s), and increased the precipitation by 35%. The authors of Monday’s study write, “Moreover, the storm was riding on sea levels that were higher by about 7.5” (19 cm) because of global warming. Although perhaps only one-half to one-third of the SST increase can be blamed on global warming from human activities, it is readily apparent that the storm surge and associated damage was considerably influenced by climate change. It is quite possible that the subways and tunnels might not have flooded without the warming-induced increases in sea level and in storm intensity and size, putting a potential price tag of human climate change on this storm in the tens of billions of dollars.” Indeed, Lloyd’s of London estimated that the amount of sea level rise due to global warming over the past century led to an additional $8 billion in damage from Sandy’s storm surge in New York. Here is another analysis (from UCAR/NCAR AtmosNews) on the factors that went into Sandy’s surge.

Figure 2. Damage to Highway 34 along the Big Thompson River, on the road to Estes Park, Colorado in September, 2013. Image credit: Colorado National Guard.

2) Boulder, Colorado floods, 2013
In September 2013, records rains over the Front Range of the Colorado Rockies fed rampaging floods that killed at least nine people and did $2 billion in damage. An assessment published in the Bulletin of the American Meteorological Society last September concluded concluded that the flood was not made more likely or more intense by climate change, given that models were just as likely to produce heavy September rain when run for the period 1870–1900 as for 1983–2012. However, the authors of the new study write, “Extremely high SSTs off the west coast of Mexico and the associated record atmospheric water vapor amounts that flowed into Colorado as a result were instrumental in the event, and it probably would not have occurred without human-caused warming. Such an increase in atmospheric water vapor becomes concentrated when focused by topography, as it did in Boulder, and further amplified on the ground as water drains into channels and rivers. This suggests an important role for human-caused warming in those Boulder floods.”

Figure 3. There's a car under here somewhere! A Maryland resident digs out after Snowmageddon. Image credit: wunderphotographer chills.

3) Snowmaggedon, 2010
On February 5 - 6, 2010, an incredible snowstorm dubbed “Snowmaggedon” hammered Washington DC and the mid-Atlantic states, burying them under 1 - 3 feet of snow. While the blizzard was not an exceptionally strong storm--the central pressure was a rather unimpressive 986 mb at the height of the blizzard--it was an exceptionally wet storm. The melted equivalent precipitation for the blizzard exceeded three inches along its core snow belt, a phenomenal amount of moisture for a winter storm. The blizzard formed a very unstable region aloft where thunderstorms were able to build, and there were many reports of thundersnow with snowfall rates of 2 - 3 inches per hour. The authors claim that unusually high SSTs in the tropical Atlantic Ocean (1.5 °C above normal) led to an exceptional amount of moisture flowing into the storm, which resulted in very large amounts of snow. While the storm was in the right place at the right time to generate a large amount of snow, the new paper argues that the extreme snowfall amounts were magnified by ocean temperatures made warmer by climate change.

Figure 4. An infrared VIIRS image of the eye of Haiyan taken at 16:19 UTC November 7, 2013. At the time, Haiyan was at peak strength with 195 mph sustained winds. Image credit: NOAA/CIRA.

4) Super Typhoon Haiyan, 2013
Super Typhoon Haiyan hit the Central Philippines on November 8, 2013, as one of the strongest tropical cyclones in world history, with peak surface winds estimated at 195 mph by the Joint Typhoon Warning Center. Haiyan killed over 7,700 people and did at least $13 billion in damage, making it the costliest and deadliest disaster in Philippine history, and Earth's deadliest natural disaster of 2013. The new study notes that oceanic heat content (OHC) and sea level had both risen significantly in the region since 1998 as a result of the negative phase of the Pacific Decadal Oscillation. “Consequently, as the typhoon approached the Philippines, it was riding on very high SSTs with very deep support through the high OHC, and the strong winds and ocean mixing did not cause as much cooling as would normally be experienced, probably helping the storm to maintain its tremendous strength,” write the authors. “Moreover, the storm surge was undoubtedly exacerbated considerably by the sea levels, which were some 30 cm [12”] above 1993 values. Although natural variability through the PDO played a major role, there is also a global component through increased OHC from the Earth’s energy imbalance."

Climate Change Extreme Weather

Long-Lived Bill Meets its Demise in Mid-Atlantic

By: Bob Henson , 4:37 AM GMT on June 22, 2015

The books have finally been closed on Post-Tropical Cyclone Bill, which dumped heavy rain and clung to life as an identifiable system during a trek of more than 1,000 inland miles. The last advisory on Bill was issued by the NOAA Weather Prediction Center at 8:00 am EDT Sunday, almost five days after the cyclone made landfall on Matagorda Island, Texas, as a 60-mph tropical storm at 11:55 am CDT Tuesday, June 16. The poorly defined circulation associated with Bill was located on Sunday morning about halfway between Baltimore and Philadelphia, with maximum sustained winds a paltry 10 mph. Bill wasn’t designated as a tropical storm until 10:00 pm CDT on Monday, June 15, so an impressive 89% of Bill’s lifespan as a named entity (115 of 129 hours) took place inland. The National Hurricane Center handed off responsibility for Tropical Depression Bill to NOAA’s Weather Prediction Center at 4:00 am CDT Wednesday morning, when Bill was located south of Waco, TX. The system held together as a tropical depression much longer than expected--until 4:00 pm CDT Saturday afternoon (a total of 78 hours), when it was located about 65 miles NNW of Jackson, KY.

According to Weather Channel tropical expert Michael Lowry, the average post-landfall lifespan of 131 inland tropical cyclones since 1970 was just 36 hours, and only 12 of those systems lasted 78 hours or longer as inland tropical storms or depressions. The longest-lived was an unnamed, posthumously recognized tropical storm in mid-August 1987 that persisted for almost 7 days as a tropical cyclone after it made landfall, making only a brief dip into the northern Gulf along a track from Louisiana to Georgia.

Figure 1. This satellite/radar overlay from 8:30 am CDT Saturday, June 20, shows the still-robust fingerprint of clouds and thunderstorms around Bill--then still a tropical depression, although with some hybrid characteristics evident--as it moved along the Ohio Valley between Louisville and Cincinnati. Image credit: Greg Postel/Weather Channel.

Bill was especially robust on Wednesday afternoon and evening over the Texas/Oklahoma border area, where it produced isolated rainfall totals of more than a foot. As Bill drifted northward, it came under the influence of a weak upper-level trough that infused it with energy and allowed its moisture to stream northeastward. Some of Bill’s tenacity over Texas and Oklahoma may have resulted from the brown ocean effect, where extremely moist soils send large amounts of latent heat into the atmosphere. In the wake of Bill, yet another round of heavy thunderstorms fell over the border area around Lake Texoma on Sunday afternoon, pushing 60-day rainfall totals well into the phenomenal 35” - 40” range over several counties. Two people were rescued after a bridge collapse on Sunday afternoon along a farm-to-market road (FM 118) about 50 miles northeast of Dallas. The Red River at Gainesville, TX, reached a record crest of 42.05 feet on Friday, nearly swamping the Interstate 35 bridge before subsiding. The previous record crest of 40.08 feet occurred on May 31, 1987, during a well-established El Niño event, as is the case this year.

Figure 2. The Red River (separating Oklahoma and Texas) reached a record crest on Friday of 42.05 feet. Image credit: NOAA Advanced Hydrologic Prediction Service/U.S. Geological Survey

Figure 3. Floodwaters from the Washita River inundate a bridge on State Highway 377 south of Tishomingo, OK. The nearby Cumberland Levee was breached on Sunday after being overtopped during the weekend, but the water was pouring into an unpopulated containment basin. Image credit: Tulsa District, U.S. Army Corps of Engineers.

Rains that jump ahead of tropical cyclones
Along with the downpours near its center, heavy rains also developed well northeast of Bill, as rich moisture was channeled ahead of the system along a frontal zone from Missouri to the Appalachians. While Bill’s center was still in Texas on Tuesday night and Wednesday morning, a large cluster of thunderstorms developed in south-central Missouri, which appears to have been an unusually early-in-the-season example of a predecessor rainfall event (PRE). A 2010 study led by Tom Galarneau (then at the University at Albany, State University of New York, and now at the National Center for Atmospheric Research) analyzed 28 PREs that occurred during the period from 1995 to 2008. On average, these PREs occurred about 600 miles downstream and about 36 hours ahead of a tropical cyclone’s central rain shield. PREs tend to occur when an east-west frontal zone is intersected by, and strengthened by, an influx of deep tropical moisture in the southerly flow ahead of a tropical cyclone. “The presence of tropical cyclone moisture can turn a heavy rain event into a record-breaking high-impact heavy rain event,” noted the authors. Most of the PREs analyzed by Galarneau and colleagues occurred in August and September, and they were most common with stronger hurricanes. However, a couple of early-season PREs were associated with Tropical Storm Alberto (June 12, 2006) in the Carolinas, and Hurricane Dennis (July 9, 2005) in Florida, Georgia, and South Carolina.

Here are some of the heaviest rainfalls in each state near or ahead of Bill, as reported by NOAA’s Weather Prediction Center on Sunday:

Texas: 12.50” (Montague)
Louisiana: 4.79” (Shreveport Regional Airport)
Oklahoma: 12.53” (3 miles E of Healdton)
Arkansas: 4.42” (2 miles SE of Rogers)
Kansas: 3.64” (Coffeyville Municipal Airport)
Missouri: 8.25” (4 miles WNW of Fordland)
Illinois: 5.14” (Cooks Mill)
Indiana: 6.72” (Grissom Air Force Base/Peru)
Kentucky: 3.54” (Henderson City)
Ohio: 5.11” (Lima/Allen County Airport)
Pennsylvania: 1.93” (Harrisburg/Capital City Airport)
West Virginia: 1.68” (Parkersburg/Wilson)
Virginia: 3.85” (Fort Belvoir/Davison Air Force Base)
District of Columbia: 2.37” (Reagan Washington National Airport)
Maryland: 2.50” (1 mile NNE of Cheltenham)

A quiet week ahead in the tropics
No major tropical developments are expected over the next several days, with wind shear relatively high across much of the deep tropics of the North Atlantic and North Pacific.

Thanks go to Sheldon Kusselson (NOAA/NESDIS) and Michael Lowry, Stu Ostro, and Greg Postel (The Weather Channel) for data, graphics, and perspective related to Bill.

Bob Henson

Figure 4. Visible satellite image of Bill’s circulation from around 7:00 pm CDT on Friday, June 19, when the center was close to the Mississippi and Ohio River confluence. Thunderstorms along an inflow band extended to northeast Texas and southwest Arkansas (see circle and Figure 5 below). Image credit: NOAA.

Figure 5. Stu Ostro (The Weather Channel) photographed these thunderstorms on Friday evening associated with a convergence band in the Arklatex region, well to the southwest of Bill’s center. Image credit: Stu Ostro.


Earth has its Warmest May and Warmest Year-to-Date Period on Record

By: JeffMasters, 1:01 PM GMT on June 19, 2015

May 2015 was Earth's warmest May since global record keeping began in 1880, said NOAA's National Centers for Environmental Information (NCEI) on Thursday. NASA rated May 2015 as the 2nd warmest May on record. May 2015's warmth makes the year-to-date period (January - May) the warmest such period on record, according to both NOAA and NASA, and it is likely that 2015 will be Earth's second consecutive warmest year on record. Five of the ten warmest months in recorded history have occurred in the past six months, according to NOAA:

NOAA's top ten warmest global monthly departures from average
1) 0.89°C, Mar 2015
1) 0.89°C, Feb 2015

3) 0.88°C, Jan 2007
4) 0.87°C, May 2015
4) 0.87°C, Feb 1998
6) 0.84°C, Dec 2014
6) 0.84°C, Mar 2010
8) 0.83°C, Nov 2013
9) 0.82°C, Apr 2010
10) 0.81°C, Jan 2015

Global ocean temperatures during May 2015 were the warmest on record, and global land temperatures were tied for warmest on record. Global satellite-measured temperatures in May 2015 for the lowest 8 km of the atmosphere were the 5th or 4th warmest in the 37-year record, according to the University of Alabama Huntsville (UAH) and Remote Sensing Systems, respectively.

Figure 1. Departure of temperature from average for May 2015, the warmest May for the globe since record keeping began in 1880. Record warmth occurred across most of Alaska, parts of tropical South America, much of southern Africa and The Middle East, and parts of northwestern Siberia. Only part of the central United States, far west central Australia, Iceland, and part of Far East Russia observed temperatures characterized as "cooler than average" for May. Image credit: National Centers for Environmental Information (NCEI) .

Figure 2. Departure of temperature from average for the globe for 12-month periods ending in May each year, starting in 1880 and ending in 2015. There is no evidence of a long term slow-down in global warming. Image credit: NOAA.

Deadliest weather disaster of May 2015: India's brutal heat wave
The deadliest weather-related disaster of May 2015 was an intense heat wave in India that killed approximately 2,500 people. According to statistics from EM-DAT, the International Disaster Database, the 2015 heat wave in India was their second deadliest heat wave and Earth's fifth deadliest heat wave ever recorded; the heat wave was also the planet's 11th deadliest weather-related disaster since 2000. Note that heat waves and droughts hold three of the top five spots on the list of deadliest disasters since 2000, suggesting that society is not prepared for the increase in the intensity of heat waves and droughts that is already occurring due to a warming climate:

Death Tolls From Earth's Deadliest Weather-Related Disasters Since 2000
1) Cyclone Nargis, Mayanmar, 2008: 138,366
2) Heat wave, Europe, 2003: 71,310
3) Heat wave, Russia, 2010: 55,736
4) Drought, Somalia, 2010 - 2011: 20,000
5) Typhoon Haiyan, Philippines, 2013: 7,354
6) Flood, India, 2013: 6,054
7) Cyclone Sidr, Bangladesh, 2007: 4,234
8) Heat wave, Europe, 2006: 3,418
9) Hurricane Jeanne, Haiti, 2004: 2,754
10) Flood, Haiti, 2004: 2,665
11) Heat wave, India, 2015: 2,500
12) Flood, Pakistan, 2010: 1,985
13) Typhoon Bopha, Philippines, 2012: 1,901
14) Hurricane Katrina, U.S., 2005: 1,833
15) Landslide, China, 2010: 1,765

Three billion-dollar weather disasters in May 2015
Three billion-dollar weather-related disasters hit the Earth last month, according to the May 2015 Catastrophe Report from insurance broker Aon Benfield: a severe weather outbreak and flooding on May 23 - 28 in the Central U.S. that caused at least $1 billion in damage; flooding in China that caused $1.15 billion in damage; and the on-going drought in California and neighboring states that now has a price tag of at least $3 billion.

Disaster 1. "Exceptional" drought--the most severe classification made--continued across California during the month of May. A study conducted by the UC Davis Center for Watershed Sciences on behalf of the California state government concluded that statewide economic losses from the drought will top $2.7 billion in 2015. Including damage from neighboring states--particularly Washington--the overall total losses will be at least $3.0 billion. In this photo from May 24, 2015, we see houseboats moored on a shrinking arm of California's Oroville Lake reservoir, which was at 52 percent of its usual level. Image credit: MARK RALSTON/AFP/Getty Images.

Disaster 2. A wave of severe thunderstorms, tornadoes, and torrential rains swept through the heart of the U.S. May 23 - 28, killing 32 people and causing over $1 billion in damage. The heaviest flooding and damage was in Texas and Oklahoma, which suffered their rainiest month in recorded history. In this photo, we see a severe thunderstorm with golfball-sized hail that pounded Wetmore, KS on May 25, 2015. Image credit: Wunderphotographer idzrvit.

Disaster 3. Flooding, landslides and hail from seasonal rains in southern China from May 18 - 22 killed at least 48 people and did $1.15 billion in damage in the provincial regions of Fujian, Jiangxi, Hunan, Guangdong, Guangxi, and Guizhou. An estimated 87,000 homes were damaged or destroyed, and more than 100,000 hectares (247,000 acres) of cropland were inundated. This picture taken on May 20, 2015 shows a rescuer with a life buoy in floodwaters during an intense rainstorm that killed 7 people in Xiamen, in eastern China's Fujian province. Image credit: STR/AFP/Getty Images.

Arctic sea ice falls to 3rd lowest May extent on record
Arctic sea ice extent during May 2015 was the 3rd lowest in the 36-year satellite record, according to the National Snow and Ice Data Center (NSIDC). By the end of May, sea ice extent had fallen to an all-time record low extent for the date, and continued to track at an extent between the lowest and 4th lowest on record during the first half of June. The near-record late May - early June retreat in sea ice was due to wind patterns favorable for sea ice loss combined with sunnier than usual weather in the Arctic.

Notable global heat and cold marks set for May 2015
Hottest temperature in the Northern Hemisphere: 49.8°C (121.6°F) at Larkana, Pakistan, May 21
Coldest temperature in the Northern Hemisphere: -44.8°C (-48.6°F) at Summit GEO, Greenland, May 2
Hottest temperature in the Southern Hemisphere: 38.8°C (101.8°F) at Skukuza, South Africa, May 16
Coldest temperature in the Southern Hemisphere: -81.2°C (-114.2°F) at Concordia, Antarctica, May 28

Major stations that set (not tied) new all-time heat or cold records in May 2015
Truong Sa, Spratly Islands (Vietnam), max. 35.9°C, May 16
Khammam (India), max. 47.6°C, May 23
Nainital (India), max. 31.0°C, May 26
Mussoorie (India), max. 36.0°C, May 26
Con Cuong (Vietnam), max. 42.7°C, May 30 (Tied all-time national high set at Tuong Duong on May 12, 1966)
Quy Hop (Vietnam), max. 42.6°C, May 30

* On May 14 Palau tied its all-time hottest temperature on record with 34.4°C at Babelthuap Airport, a value which was set in few occasions before both at the airport and at Nekken Forestry.

New all-time national and territorial heat records set or tied in 2015
As of June 15, 2015, eight nations or territories have tied or set all-time records for their hottest temperature in recorded history thus far in 2015, and one (Israel) has set an all-time cold temperature record. For comparison, only two nations or territories set all-time heat records in 2014, and nine did in 2013. The most all-time national heat records held by any year is nineteen in 2010. Most nations do not maintain official databases of extreme temperature records, so the national temperature records reported here are in many cases not official. I use as my source for international weather records researcher Maximiliano Herrera, one of the world's top climatologists, who maintains a comprehensive list of extreme temperature records for every nation in the world on his website. If you reproduce this list of extremes, please cite Maximiliano Herrera as the primary source of the weather records. Wunderground's weather historian Christopher C. Burt maintains a database of these national heat and cold records for 235 nations and territories on's extremes page. Here are the all-time national or territorial heat and cold records set so far in 2015:

Vietnam tied its national heat record of 42.7°C (108.9.0°F) at Con Cuong on May 30.
Palau tied its national heat record of 34.4°C (94.0°F) at Koror Airport on May 14.
Venezuela set a new national heat record of 43.6°C (109.9°F) at Coro on May 29. Previous record: 42.0°C (107.6°F) at Machiques, Zulia State in February 1983.
Laos tied its national heat record of 42.0°C (107.6°F) at Thakhek on May 20.
Ghana set a new national heat record of 43.3°C (109.9°F) at Navrongo on May 10. This is the third time this year Ghana has tied or set a new all-time heat record. Previous records: 43.1°C (109.6°F), set the previous day, on May 9, and 43.0°C (109.4°F) on February 12.
Cocos Islands (Australian territory) tied their all-time heat record with 32.8°C (91.0°F) on May 8.
Equatorial Guinea set a new national heat record of 35.5°C (95.9°F) at Bata on March 17. Previous record: 35.3°C (95.5°F) at Malabo in February 1957.
Wallis and Futuna Territory (France) set a new territorial heat record with 35.5°C (95.9°F) on January 19 at Futuna Airport.

Israel set a new national cold record of -14.2°C (6.4°F) at Merom Golan on January 10.

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

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

Have a great weekend, everyone!

Jeff Masters

Climate Summaries

The Poor and the Earth Are Crying: The Pope's Encyclical on Climate Change

By: Jeff Masters and Bob Henson , 1:01 PM GMT on June 18, 2015

"Earth herself, burdened and laid waste, is among the most abandoned and maltreated of our poor; she groans in travail."

One of the largest and oldest institutions on Earth--the Catholic Church--weighed in with these words today on the need to address the threat climate change poses to our common home. Pope Francis officially released his third papal encyclical, “Laudato Sii” (Be Praised), from the Vatican on Thursday. The 180-page encyclical is an enormous milestone in climate change awareness, and is sure to influence the critical December 2015 meeting in Paris to negotiate a new global binding treaty to limit emissions of heat-trapping greenhouse gases.

Figure 1. Pope Francis holds an olive tree at the Vatican on September 1, 2014. Image credit: VINCENZO PINTO/AFP/Getty Images.

Papal encyclicals are among the highest-level documents produced by the Catholic Church. Each one focuses on a topic of keen importance to the Church itself or to society at large, and this time around the Pope specifically addresses “every person who inhabits this planet.” It is the seventh encyclical of the 21st century and the first one ever devoted to an environmental issue. In it, the Pope frequently invokes the life of his namesake, Saint Francis of Assisi, the patron saint of all those who study ecology and a champion for the poor and abandoned. The emphasis is not on climate science itself: the Pope agrees that rising global temperatures are primarily due to fossil fuel use, which is consistent with the conclusions of numerous national science societies and the Intergovernmental Panel on Climate Change. The Pope’s main concern is with the ethical and moral facets of the problem, and our responsibility as stewards of Earth to deal with it. Here are some of the main themes put forth:
-- The book of Genesis tells us to "have dominion over the earth", which would seem to favor savage exploitation of nature by domineering and destructive humans. This is not a correct interpretation of the Bible, as Genesis also tells us to "till and keep" the garden of the world.
-- What we are facing is primarily a spiritual crisis: "The misuse of creation begins when we no longer recognize any higher instance than ourselves, when we see nothing else but ourselves. For human beings to destroy the biological diversity of God’s creation; for human beings to degrade the integrity of the earth by causing changes in its climate, by stripping the earth of its natural forests or destroying its wetlands; for human beings to contaminate the earth’s waters, its land, its air, and its life–these are sins. For to commit a crime against the natural world is a sin against ourselves and a sin against God." He argues strongly that we can work together to solve this spiritual crisis through right action, and urges us to "replace consumption with sacrifice, greed with generosity, wastefulness with a spirit of sharing."

-- Humans are mostly responsible for global warming: “A very solid scientific consensus indicates that we are presently witnessing a disturbing warming of the climatic system. In recent decades this warming has been accompanied by a constant rise in the sea level and, it would appear, by an increase of extreme weather events, even if a scientifically determinable cause cannot be assigned to each particular phenomenon. Humanity is called to recognize the need for changes of lifestyle, production and consumption, in order to combat this warming or at least the human causes which produce or aggravate it. It is true that there are other factors (such as volcanic activity, variations in the earth’s orbit and axis, the solar cycle), yet a number of scientific studies indicate that most global warming in recent decades is due to the great concentration of greenhouse gases (carbon dioxide, methane, nitrogen oxides and others) released mainly as a result of human activity.”

-- While technology has brought tremendous progress, "our immense technological development has not been accompanied by a development in human responsibility, values and conscience."

-- Technology based on fossil fuels--particularly coal, but also oil and to an extent, natural gas--must be replaced progressively and without delay: "There is an urgent need to develop policies so that, in the next few years, the emission of carbon dioxide and other highly polluting gases can be drastically reduced, for example, substituting for fossil fuels and developing sources of renewable energy."
-- The rich, highly industrialized countries that have contributed the greatest emissions of greenhouse gases have the greatest responsibility to contribute to solution of the problems that they have caused. The poor countries, who have contributed little to the build-up of carbon dioxide in the atmosphere, will suffer the greatest harm, since they do not have the resources to adapt.
-- "Obsession with a consumerist lifestyle, above all when few people are capable of maintaining it, can only lead to violence and mutual destruction." People should change their lifestyles to consume less, and use the power of their purchases to positively affect the world: "purchasing is always a moral--and not simply economic act."
-- Action is being delayed by rich special interests that profit from the current situation: "The failure of global summits on the environment make it plain that our politics are subject to technology and finance. There are too many special interests, and economic interests easily end up trumping the common good and manipulating information so that their own plans will not be affected. The alliance between the economy and technology ends up sidelining anything unrelated to its immediate interests. Consequently the most one can expect is superficial rhetoric, sporadic acts of philanthropy and perfunctory expressions of concern for the environment, whereas any genuine attempt by groups within society to introduce change is viewed as a nuisance based on romantic illusions or an obstacle to be circumvented."

The encylical concludes with this powerful prayer:
The poor and the earth are crying out.
O Lord, seize us with your power and light,
help us to protect all life,
to prepare for a better future,
for the coming of your Kingdom
of justice, peace, love and beauty.
Praise be to you!

How will the encyclical be received?
Given that there are more than 1.2 billion Catholics worldwide, this encyclical has the potential to directly influence a large segment of the world’s population. Some 20% of the U.S. population is Catholic (the United States ranks among the five countries with the most Catholics), so the encyclical should resonate widely here. The broad popularity of Pope Francis--about 7 in 10 Americans have a favorable view of him--will add to the encyclical’s reach.
As explained in this Q&A from the Yale School of Forestry and Environmental Science: “While encyclicals do not compel Catholics to believe and act in accordance with what is said, the expectation is that all Catholics (and it is hoped all people of good will) will use the teaching as guidance for their life style and moral commitments. For theologians, both clerical and lay, relevant encyclicals have traditionally informed their scholarship and continue to do so.”
Francis is not the first Pope to lay claim to environmental awareness. The Yale Q&A cites several precedents, including the 1972 address “A Hospitable Earth for Future Generations,” presented by Pope Paul VI at the Stockholm Conference on the Environment. In his book Why We Disagree About Climate Change, climate scientist Mike Hulme asserts that “all of the world’s institutionalized faiths are strong on the duty of care for the created world. There is a reverence for life--a sacredness--that is central to nearly all religious writings, even if expressed in different ways.”
Surveys that compare attitudes on the environment across U.S. religious affiliations do show some major differences. But political affiliation may play the more crucial role, even for those within a particular sect. A recent survey by the Pew Research Center found sharp divisions among Catholics on climate change, largely mirroring a broader partisan divide. The climate change cause has likely become more divisive than it otherwise would have been, in part, because its most famous proponent has been a politician, Al Gore. Even before the encyclical’s release, 2016 presidential candidate Rick Santorum (a Catholic) urged the Pope to “leave science to the scientists” and avoid “controversial scientific theories,” an illustration of how politics can trump religious affiliation when it comes to the highly polarized world of climate change. Katharine Hayhoe--who plays a major role in the U.S. discussion, as a person of faith and as a climate scientist based at Texas Tech University--weighed in on the intersection of climate, politics, and religion in recent essays for the websites Prairie Fire and The Conversation. In response to the question “Will evangelicals care (about the encyclical)?”, Hayhoe responds in the affirmative: “It’s because the theology on which we need to agree to care about climate change is so simple. Evangelical or Catholic, Episcopal or Apostolic, we all believe God created the world, even if we’re still arguing over the process by which that was accomplished.”
Today’s encyclical will add to the drumbeat building toward the crucial UN Conference of the Parties 21 meeting this December in Paris, where the successor treaty to the Kyoto protocol is expected to take shape. Between now and then, the Pope will continue bringing his message to the world at large, including the U.S. Congress in an address scheduled for September.
WU climate blogger Ricky Rood has more thoughts on the significance of this week’s encyclical.
Jeff Masters and Bob Henson

Climate Change Politics Climate Change

Tropical Depression Bill Still Posing Major Flood Risk

By: Bob Henson and Jeff Masters , 4:10 PM GMT on June 17, 2015

Although it was downgraded to tropical-depression status by the National Hurricane Center at 1:00 am Wednesday, the system known as Bill remains a serious threat for flood-producing rain over a belt extending through central Texas across eastern Oklahoma and into the Midwest. NHC issued its final advisory on Bill at 4:00 am CDT, when the center of circulation was located about 45 miles south of Waco, TX. Top winds were at 35 mph, and Bill was moving north at 13 mph with a minimum central pressure of 1000 mb. National Weather Service radar showed the center of Bill approaching the Dallas-Fort Worth area at 10:00 am CDT, with a large shield of moderate to occasionally heavy rain north of its center. Responsibility for monitoring TD Bill has been handed from NHC to the NOAA’s Weather Prediction Center, which is monitoring Bill’s rainfall and the resulting flood threat.

Figure 1. Radar display from WU’s Storm app at 10:05 am CDT Wednesday, June 17.

A persistent inflow band extended from Bill’s center to the Texas coast, with large rainfall totals accumulating between Corpus Christi and Houston (see Figure 2). NOAA/WPC warned on Wednesday morning that storm totals of a foot of rain could occur beneath the band extending south from Bill to the coastline. This morning, one rain gauge near El Campo, TX, maintained by the Lower Colorado River Authority reported 11.40” over the past 24 hours. “These rainfall amounts would produce flash flooding in an average year...but flash flooding during this event may be very widespread and particularly dangerous given the super-saturated soils in parts of Texas,” noted WPC in a 9:23 am CDT advisory.

Figure 2. 24-hour rainfall estimates from 7:00 am CDT Tuesday, June 16, through Wednesday, June 17, derived from raingauges and radar data and supplemented by satellite information. Image source: NOAA/NWS Advanced Hydrologic Prediction Service.

Tonight: Red River under the gun
As Bill continues sliding northward, it’s expected to maintain its identity as a coherent low-pressure center for at least the next day or so. Some models continue to suggest that Bill could even restrengthen slightly tonight over southeast Oklahoma, a possibility raised in recent studies of the “brown ocean effect.” As discussed in our post on Monday, there’s an increasing amount of research on the process by which a tropical cyclone can re-intensify well inland if soils are sufficiently moist. Both Texas and Oklahoma saw the wettest month in their weather histories during May, and soils remain saturated across much of the area. Since the brown-ocean reintensification effect is a rare beast, we might not expect forecast models to latch onto it. The 1200 GMT Wednesday run of the high-resolution HRRR short-range model suggested a slight deepening of Bill’s central pressure late this evening near the Texas-Oklahoma border, while the longer-range NAM model from 1200 GMT Wednesday indicates that Bill will at least maintain its current level of organization into Thursday, when the system is predicted to slow to a crawl over southeast Oklahoma. Eventually, Bill will be get pulled into an existing frontal boundary and should begin to lose its definition near southern Missouri by Saturday.

Figure 3. Projected three-day precipitation totals from the NOAA Weather Prediction Center, for the period from 1200 GMT June 17 to June 20, show the expected track of Bill around the high-pressure center in the southeast U.S. Image credit: NWS/WPC.

The NAM model predicts widespread 5” – 10” rainfall amounts from the DFW area across eastern Oklahoma to southwest Missouri from Wednesday through Saturday morning. A large arc of flash flood watches remained in effect on Wednesday morning from the Texas coast to southern Illinois, and Bill’s remnants are likely to produce heavy rain for days to come as they traverse the preexisting frontal boundary. Models indicate a very sharp gradient along the northwest side of the rains associated with Bill, so Oklahoma City and Tulsa may be close to the edge of the heaviest amounts. However, the NWS offices in both cities are warning of a potentially life-threatening flooding event where the rains do fall. Rivers and reservoirs still engorged from Texas and Oklahoma east to Arkansas and Louisiana will not be able to handle much additional rain from Bill, so in addition to flash flooding, mainstem flooding will likely emerge as a major concern toward the weekend, including along the Arkansas and Red Rivers and their major tributaries. Major flooding was already being reported on Wednesday morning along several rivers in the region monitored by the NWS’s Arkansas–Red Basin River Forecast Center.

Figure 4. The circulation around Tropical Storm Bill dwarfed that around Hurricane Carlos as of late Tuesday, June 16. Image credit: @NOAASatellites.

Carlos hangs on to tropical storm status
After briefly regaining hurricane strength yesterday, Carlos weakened dramatically overnight as its circulation hugged the northwest coast of Mexico. The small size of Carlos and its location near the coast has given forecasters headaches and led to large variations in intensity. The 10:00 am CDT advisory from NHC gives Carlos only a few more hours of life as a tropical cyclone, with the system projected to become a remnant low by Thursday morning, if not sooner. Satellite loops this morning showed an rapidly disorganizing system. Heavy rains will persist as Carlos and its moisture interact with the Sierra Madre del Sur mountain range, which will cause flash flooding and mudslides. On the heels of Hurricane Blanca, which made landfall over Baja California on June 8 a month earlier than any previous landfall on record for the peninsula, Carlos will be the second tropical cyclone of at least tropical-storm strength to make landfall this year on the Pacific coast of Mexico. According to the NOAA Historical Hurricanes website, there have been only two other years since accurate record keeping began in 1951 that the Northeast Pacific has seen two landfalling tropical cyclones so early in the year: 1951 (by June 1) and 1971 (by June 17.)

Bob Henson and Jeff Masters


Bill Makes Landfall in Texas; Greatest Impact Still to Come

By: Bob Henson and Jeff Masters , 12:52 AM GMT on June 17, 2015

Less than 12 hours after it was named, Tropical Storm Bill pushed ashore near Matagorda Bay, Texas, at 11:45 am CDT Tuesday. Peak winds at landfall were 60 mph, with a gust to 53 mph reported at both Palacios and Port O’Connor, Texas. Some minor coastal flooding was observed, with the water level at Port Lavaca about 3 feet above normal, but on the whole Bill caused relatively little trouble along the Texas shore. That may not be the case inland over the next couple of days, as Bill churns slowly north and its showers and thunderstorms continue to organize.

Figure 1. GOES satellite image of Tropical Storm Bill as it neared the Texas coast. Image credit: NASA/GOES Project Science.

Figure 2. Bill’s thunderstorm activity continued to organize on Tuesday evening even with the center now inland. This NWS radar image from the WU Storm app is from 7:20 pm Tuesday, June 16.

At 7:00 pm CDT Tuesday, Bill was located about 10 miles northeast of Victoria, TX, with a central pressure of 999 mb and peak sustained winds of 45 mph. Bill wobbled westward this afternoon, but it was moving north-northwest at 9 mph as of 7 pm Tuesday. An observer in northwest Houston reported 0.92” of rain in just 15 minutes on Tuesday afternoon. Even as the storm weakens to a depression by Wednesday morning, Bill should maintain its identity as a distinct surface low. Multiple models are suggesting that Bill could even reorganize somewhat over northeast Texas or southeast Oklahoma late Wednesday or early Thursday. This uncommon occurrence is being made possible by extremely wet soils over much of Texas and Oklahoma, which just saw the wettest month in their history. As discussed in our post Monday, there’s an increasing amount of research on the process by which a tropical cyclone can re-intensify well inland if soils are sufficiently moist--what’s been called the “brown ocean effect.”

Figure 3. Projected three-day precipitation totals from the NOAA Weather Prediction Center, for the period from 0000 GMT June 17 to June 20, show the expected track of Bill around the high-pressure center in the southeast U.S. Image credit: NWS/WPC.

Heavy rain threat still on tap
Bill’s track inland was just far enough west of Houston that the metro area was largely spared from heavy rain on Tuesday afternoon. Convection may organize somewhat tonight, as the surface layer decouples from the rest of Bill, and there is likely to be a core of intense rainfall somewhere near the I-35 and I-45 corridors of central Texas on Wednesday. The Dallas-Fort Worth area will be in Bill’s crosshairs by Wednesday afternoon and evening, with the local NWS office warning of a risk of widespread 3 - 6” rains and local amounts of 6” - 12” near Bill’s center and where persistent banding occurs. Tornadoes are also quite possible tonight and Tuesday, especially northeast of Bill’s center; a long-lived tornado watch is in effect for much of southeast Texas through midnight CDT Tuesday night. With soils saturated, the risk of flash flooding is serious, particularly over north-central and northeast Texas late Wednesday and over roughly the southeast half of Oklahoma from late Wednesday into Thursday. Rivers and reservoirs still engorged from Texas and Oklahoma east to Arkansas and Louisiana will not be able to handle much additional rain from Bill, so flooding may be a continued headache for days to come. Shreveport, LA, has already seen extensive damage from some of the highest levels since 1945 along the Red River.

As Bill moves north, its moisture will intersect a weak surface front that arcs from central Oklahoma into the Ohio Valley, and bands of heavy rain may develop well north of the actual circulation. Flash flood watches were in effect on Tuesday night all the way from south Texas to central Illinois.

Figure 4. Rainfall in Mexico from Hurricane Carlos and Tropical Storm Bill for the 24 hours ending at 8 am Tuesday June 16, 2015. The maximum rainfall amount was 4.15" (105.5 mm) at Pajaritos; just under 4" fell near Puerto Vallarta. Image credit: CONAGUA.

Hurricane Carlos proving difficult to predict
An Air Force hurricane hunter aircraft found that Hurricane Carlos was stronger than expected on Tuesday afternoon, with top winds near 90 mph. Maximum sustained winds were reported at 85 mph in the 7:00 pm CDT advisory. Carlos continues its slow northwest motion at 5 mph, almost parallel to and about 80 miles offshore from the coast. Fortunately, Carlos is a very small storm, with tropical storm-force winds that only extend outwards about 45 miles. So far its heavy rains have mostly stayed offshore, though a few mountainous areas to its north received about 4" of rain in the 24 hour period ending at 8 am Tuesday. Satellite loops showed an intermittent eye today, with the hurricane's heavy thunderstorms remaining just offshore from the coast near Manzanillo, Mexico. Dry air and a more stable atmosphere should lead to weakening on Wednesday, but this forecast is low-confidence. The storm's small size has made it difficult to predict for the computer models, and Carlos may be able to maintain hurricane strength longer than expected. Carlos will likely bring heavy rains of 3 - 6 inches to portions of the Southwest Mexican coast through Thursday, which will cause flash flooding and mudslides.

We’ll be back with an update on Wednesday morning.

Bob Henson (Bill), Jeff Masters (Carlos)


Tropical Storm Bill Moving Ashore Over Texas

By: Jeff Masters , 1:48 PM GMT on June 16, 2015

Tropical Storm Bill is pushing ashore over the Central Texas coast, bringing torrential rains and sustained winds near 60 mph. At 7:45 am CDT, the Brazos 538 oil rig off the Central Texas coast recorded sustained winds of 41 mph gusting to 64 mph. While heavy flooding rains are the main threat from Bill, a few weak tornadoes will also be be possible today, particularly in the Houston metropolitan area. NOAA's Storm Prediction Center is giving a 40% chance that they will issue a tornado watch for the area today. Radar out of Corpus Christi and satellite images showed that Bill's heavy thunderstorms increased markedly in areal coverage and intensity on Tuesday morning, and its a good thing the storm did not have another twelve hours over water, or it would have become a hurricane. Bill's landfall in Texas makes the U.S. two-for-two so far for landfalls this hurricane season: Tropical Storm Ana, the first named storm of the season, hit South Carolina back on May 10. The last time the first two named storms of the season both made landfall in the U.S. was in 2001, when Tropical Storm Allison hit Texas and Tropical Storm Barry hit the Florida Panhandle. Bill is the fourteenth named storm to form in the Gulf of Mexico in the month of June since 1950 (thanks to Phil Klotzbach for this stat.)

Figure 1. Tropical Storm Bill near landfall in Texas as seen from the Corpus Christi radar at 8:29 am CDT June 16, 2015.

Figure 2. Tropical Storm Bill as seen from the International Space Station on Monday afternoon, June 15, 2015. Bill had not yet been named at this time, but was generating sustained winds of 45 mph over the Gulf of Mexico. Image credit: Scott Kelly.

Bill a major flood threat
A huge area of flash flood watches stretches from Central Texas to Illinois in anticipation of the arrival of tropical moisture from Bill. Bill poses its most serious flood threat along a swath from eastern Texas into eastern Oklahoma, where up to 8" of rain is possible through Wednesday. Both states just experienced the wettest single month in their history during May, and soils remain near saturation. Houston lies at the edge of the predicted heaviest swath of rain, and Dallas is squarely in the bulls-eye. Steering currents will be weak as the system rotates clockwise around a strong, hot dome of high pressure over the Southeast late in the week, and Bill's remnants are expected to dump as much as five inches of rain over portions of Missouri and Illinois on Thursday and Friday.

Figure 3. Projected five-day precipitation totals from the NOAA Weather Prediction Center, for the period from 8:00 am June 16 to June 21, show the expected track of Bill around the high-pressure center in the southeast U.S. Image credit: NWS/WPC.

We'll have an update on Bill this afternoon.

Jeff Masters


Dangerous Flood Potential in Texas, Oklahoma from Invest 91L

By: Bob Henson and Jeff Masters , 3:46 PM GMT on June 15, 2015

Residents of the Southern Plains need to keep a wary eye on tropical disturbance Invest 91L as it moves into the northwest Gulf of Mexico. The storm is already bringing winds near tropical storm force over the northern Gulf of Mexico; the South Marsh 268 oil rig located about 50 miles south of the Central Louisiana coast measured sustained winds of 40 mph, gusting to 47 mph, at 8:35 am CDT Monday morning. The Hurricane Hunters, flying at an elevation of 1000 feet, found flight level winds of up to 55 mph and surface winds in excess of tropical storm force (39+ mph) on the northeast side of 91L's center near 9:15 am EDT. Although 91L has tropical storm-force winds, the plane has not yet found a well-defined surface circulation, and the system did not qualify to be named Tropical Storm Bill by the National Hurricane Center on Monday morning. Satellite images showed that 91L's heavy thunderstorms have increased in intensity, and were beginning to consolidate near the low-level center of circulation, which was becoming much more defined. Wind shear on Monday morning was high, 15 - 25 knots, but rising air from 91L's thunderstorms should gradually erode the upper-level low situated above 91L, replacing it with an upper-level high that will help ventilate the developing cyclone. Sea-surface temperatures are increasingly warm ahead of 91L, with unusually high readings for mid-June of 28 – 30°C (82° – 86°F) located near the middle and upper Texas coast. These warm SSTs and the improved upper-level outflow should give 91L a brief window of potential intensification before landfall on Tuesday morning. In their 8 am EDT Monday Tropical Weather Outlook, NHC gave 2-day and 5-day odds of development of 80%. Landfall of 91L should occur Tuesday morning along the Texas coast, according to the 00Z runs of the GFS and ECMWF models.

Figure 1. Invest 91L approaching the coast of Texas as seen by the MODIS instrument at approximately 2:30 pm EDT June 15, 2015. Image credit: NASA.

Regardless of whether or not 91L becomes Tropical Storm Bill before it makes landfall, the system will post a distinct threat of serious flooding over a broad swath from eastern Texas into Oklahoma. Both states just experienced the wettest single month in their history, and soils remain near saturation. Even without such a worrisome precondition, systems like 91L are notorious for producing enormous amount of rain, sometimes with tragic results. 91L has a large and very moist circulation, and steering currents will be weak as the system slowly moves around a strong, hot dome of high pressure over the Southeast. Slow-moving systems need not be intense prior to landfall to generate huge rainfalls once they’re inland, as demonstrated by a number of Gulf of Mexico systems during June and July, when upper flow is often listless. Tropical Storm Allison is a textbook example: in June 2001, Allison drifted into east Texas, then circled back southward and made a second landfall in Louisiana, dumping as much to 38” of rain over six days across parts of the Houston area. Catastrophic flooding from Allison killed at least 41 people and caused some $9 billion in damage. Michael Lowry, hurricane specialist with The Weather Channel, points out that three of the five wettest tropical cyclones on record for the U.S. mainland occurred in Texas, and none of them attained hurricane strength. These include Allison as well as Tropical Storm Claudette, which led to a national 24-hour rainfall record on July 25-26, 1979, near Alvin, Texas—an astounding 42 inches (possibly underreported by as much as three inches due to an overflowing gauge, according to NOAA).

Figure 2. Models generally agree on a track for 91L toward the central Texas coastline.

The projected track of 91L shifted notably westward in last night’s 0000Z model runs, which suggests a larger part of hard-hit eastern Texas and southeast Oklahoma will end up on the much wetter right-hand side of the system. The atmospheric moisture content over southeast Texas is projected to be near record levels for mid-June. The juxtaposition of a slow-moving tropical system with preexisting soil saturation over this region is very unusual and particularly worrisome. Widespread rainfall of 2” – 5” is expected along 91L’s track (see Figure 3), and localized amounts beyond 10” are quite possible with training echoes, especially if the system slows as much as some models are suggesting it might. A flash flood watch is now in effect for parts of southeast Texas from Monday night through Wednesday afternoon. Tornadoes will also be a concern, including this evening over southeast Texas, as instability will be on the high side due to abundant moisture and very warm air at low levels.

Figure 3. Projected five-day precipitation totals from the NOAA Weather Prediction Center, for the period from 8:00 am June 15 to June 20, show the expected track of 91L around the high-pressure center in the southeast U.S. Image credit: NWS/WPC

The “brown ocean effect” and how it could keep 91L going
Tropical cyclones normally dissipate soon after coming ashore, but research over the last few years has shown how it’s possible for a tropical cyclone to maintain its strength or even intensify over land. The most dramatic example is Tropical Storm Erin, which weakened to a depression after landfall on the Texas coast before unexpectedly strengthening over west central Oklahoma three days later. On the night of August 18-19, 2007. Erin’s central pressure dropped from 1007 to 995 mb, and its peak sustained surface winds jumped from less than 25 mph to around 60 mph. A 2011 study in Monthly Weather Review led by Clark Evans (now at the University of Wisconsin–Milwaukee) found that large amounts of latent heat being released from unusually wet soils appear to have helped boost the storm’s intensity, although Evans is continuing to investigate the role of other factors.

Figure 4. Data from the NEXRAD radar near Oklahoma City shows Tropical Storm Erin as it formed a small eye-like feature during intensification at 1000 GMT on August 19, 2007. Image credit: Clark Evans, Russ Schumacher, and Thomas Galarneau, “Sensitivity in the Overland Reintensification of Tropical Cyclone Erin (2007) to Near-Surface Soil Moisture Characteristics,” Monthly Weather Review, doi:10.1175/2011MWR3593.1, American Meteorological Society, from NOAA/NWS data.

At the University of Georgia, Theresa Anderson and Marshall Shepherd carried out a NASA-funded global survey, published in 2013 in the International Journal of Climatology, of 227 tropical cyclones and their behavior after landfall between 1979 and 2008. While many of the cyclones dissipated in the usual fashion, and other went through extratropical transition, 16 held or increased their strength while inland. There were 8 in northwest Australia (where the systems have their own name, agukabams), 3 in India, 3 in eastern China, and 2 in North America. Those two were 2007’s Erin and a much less impressive case, 1996’s Hurricane Fran, which deepened by 1 mb while still a tropical depression over southern Ontario. Erin’s overland intensification produced three times the wind-speed increase of any other cases in the 16 examined by Anderson and Shepherd. They dubbed the inland-strengthening process the “brown ocean effect,” although in the case of red-dirt Oklahoma, it might be the “red ocean effect”! The study found that latent surface heat flux was significant in all of the cases: "The land essentially mimics the moisture-rich environment of the ocean, where the storm originated," said Anderson in a NASA news release. In a subsequent paper, the researchers (with David Radcliffe) showed that latent surface heat flux from the land can actually be larger than from the ocean for brief periods. Another common thread was a uniformly warm, moist tropical air mass across the restrengthening region. With so much water in the Texas and Oklahoma soils, and with rich atmospheric moisture already in place and set to increase, this week could end up providing a fascinating, if troublesome, test of the brown-ocean hypothesis.

Wunderground member Levi Cowan is posting daily video updates on 91L at his Tropical Tidbits website.

Figure 5. The Daily Averaged Fractional Water Index for the topmost 2 inches of soil over Oklahoma on Sunday, June 14. The index ranges from 0 (completely dry) to 1.0 (completely saturated). Image credit: Oklahoma Mesonet.

Weaker Tropical Storm Carlos still a heavy rain threat for Mexico
Tropical storm warnings are up for the Southwest coast of Mexico, as Tropical Storm Carlos continues its slow west-northwest motion at 6 mph, parallel to and about 70 miles offshore from the coast. Fortunately, Carlos is a very small storm, with tropical storm-force winds that only extend outwards about 45 miles, and so far its heavy rains have mostly stayed offshore. Satellite loops showed that Carlos had weakened some on Monday morning, with wind shear partially exposing the surface circulation to view, and the heavy thunderstorm activity waning in areal coverage and intensity. However, the storm was making a modest comeback by late Monday morning, and ocean temperatures are warm enough and wind shear is low enough to allow intensification back to a Category 1 hurricane by Tuesday morning. This intensification may be halted when Carlos gets closer to land; the 00Z Monday run of the European model predicted that Carlos would weaken significantly on Tuesday evening in advance of a Wednesday morning landfall near Manzanillo, Mexico. Dry air and a more stable atmosphere may also lead to weakening on Tuesday. Heavy rains of 5 - 10 inches will likely affect portions of the Southwest Mexican coast through Wednesday, which will cause flash flooding and mudslides. Carlos brought 1.46" of rain to Acapulco, Mexico on Saturday and Sunday. An Air Force hurricane hunter aircraft will investigate Carlos on Monday afternoon and again on Tuesday.

Bob Henson and Jeff Masters

Figure 6. Radar image of Hurricane Carlos from the Acapulco, Mexico radar, taken just before the radar failed at 8:30 pm EDT June 14, 2015. The heaviest precipitation was just offshore.

Wunderblogging hurricane expert Steve Gregory has posted a 3 pm EDT Monday afternoon update on 91L.

tropical cyclone Flood Hurricane

91L a Heavy Rain Threat for Texas/Louisiana; Hurricane Carlos a Threat to Mexico

By: Jeff Masters , 4:48 PM GMT on June 13, 2015

An area of low pressure over Mexico's Yucatan Peninsula formed Saturday morning, and has the potential to become a tropical depression over the Gulf of Mexico on Monday. The disturbance, designated Invest 91L by NHC on Saturday morning, was bringing a large area of intense thunderstorms to the Western Caribbean on Saturday afternoon, as seen on satellite images. Strong easterly winds of 29 mph, gusting to 43 mph, were observed at the Yucatan Basin buoy on Saturday morning. The heavy thunderstorm activity will push across Mexico's Yucatan Peninsula and into the southern Gulf of Mexico on Sunday, then move north to northwest towards Texas and Louisiana on Monday. The 12Z Saturday run of the SHIPS model predicted that wind shear would be marginal for development, a moderately high 15 - 25 knots, Sunday and Monday. Ocean temperatures in the Gulf of Mexico are warm enough to support a tropical storm, 27.5°C (81.5°F), and the atmosphere is very moist. In their 8 am EDT Saturday Tropical Weather Outlook, NHC gave 2-day and 5-day odds of development of 20% and 30%, respectively. The disturbance will push northwestwards over Texas by Tuesday, but it is uncertain how much rain Texas and Louisiana might get from the storm. The European model favors a more westward track into South Texas with lower rainfall totals of about 1 - 2" over Texas on Monday and Tuesday, while the GFS model shows more development of 91L and a track more towards the east, with the upper Texas coast and Louisiana coast getting about 3 - 5" of rain. Given the amount of heavy thunderstorm activity 91L has already built over the Western Caribbean, I support the wetter forecast of the GFS model for Texas and Louisiana. The Hurricane Hunters are on call to fly into 91L on Monday morning.

Figure 1. Latest satellite image of Invest 91L (right side of image) and Hurricane Carlos (left side of image.)

Figure 2. Radar image of Hurricane Carlos from the Acapulco, Mexico radar, taken at 12:15 pm EDT June 13, 2015. The eyewall had a gap in its west side, and the heaviest rain bands were just offshore.

Hurricane Carlos a heavy rain threat for Mexico
Tropical storm warnings and hurricane watches are up for the Southwest coast of Mexico, as Hurricane Carlos continues its slow intensification process. Carlos became a hurricane about 140 miles south of Acapulco, Mexico, at 11am EDT June 13, marking the second earliest date that we've observed the Northeast Pacific's third hurricane of the year. The record is held by the third hurricane of 1956, which reached hurricane strength on June 12. With very warm waters of 30°C (86°F) beneath it and wind shear a moderate 10 - 20 knots, Carlos is likely to continue a slow intensification process through Monday. On Monday and Tuesday, decreasing ocean temperatures, increasing interaction with land, and drier air will likely cause Carlos to weaken. Satellite loops and radar out of Acapulco shows that the outer spiral bands of Carlos have pushed onshore, but the storm's heaviest rains were just offshore on Saturday. Acapulco recorded sustained winds of 26 mph, gusting to 39 mph, at noon EDT Saturday. The computer models are now more unified in showing Carlos coming closer to the Mexican coast, and Carlos represents a dangerous heavy rain threat to the coast. The 00Z Saturday run of the reliable European model showed Carlos making landfall near Manzanillo, Mexico on Tuesday morning; the 06Z Saturday run of the equally reliable GFS model showed a Tuesday evening landfall near Manzanillo. Heavy rains of 5 - 10 inches will likely affect portions of the Southwest Mexican coast Saturday through Wednesday, which will cause flash flooding and mudslides.

Jeff Masters


A Close-Up Look at Last Week’s Perplexing Colorado Twisters

By: Bob Henson and Jeff Masters , 8:41 PM GMT on June 12, 2015

Early June is the most common time for tornadoes in Colorado, and last week served up a dramatic example. NOAA’s Storm Prediction Center logged 13 preliminary tornado reports in Colorado on June 4 - 6. The tornado-generating thunderstorms were spawned by weak upper-level impulses from the southwest, combined with generous low-level moisture feeding into the state from the Gulf of Mexico. Two widely photographed twisters that seemed to bend the rules of tornado formation, both on June 4, caught the attention of national press and the blogosphere.

Figure 1. This damaging tornado south of Berthoud, CO, on Thursday, June 4, was visible from a deck in Broomfield, about 20 miles to the south. Image credit: Vince Miller.

A westward-moving tornado strikes the Front Range
The strongest Colorado tornado in seven years moved from the adjacent plains toward the foothills between Boulder and Fort Collins on Thursday afternoon. Rated by the NWS Denver/Boulder office as an EF3, the tornado began about 3 miles south of the town of Berthoud, then tracked west-northwest for about 5 miles, dissipating as it approached higher terrain. Several homes were destroyed and about a dozen others damaged. The highly visible tornado was seen by many residents of Longmont and the far north suburbs of Denver.

Figure 2. A home severely damaged in the tornado near Berthoud, CO, on June 4. Image credit: NWS Denver/Boulder.

Although Colorado has recently been averaging about 60 tornadoes per year, they’re uncommon west of Interstate 25 in the populated corridor from Denver to Cheyenne, Wyoming. Moreover, westward-moving tornadoes are quite unusual anywhere in the country. Parent thunderstorms are typically steered by flow through the deep layer of the atmosphere in which the storms reside. Typically, this flow has a west-to-east component ahead of upper-level impulses, where storms are most likely to develop. A supercell thunderstorm will sometimes move to the right of the vertically averaged wind (e.g., toward the east rather than the northeast), which often increases its tornado-producing potential.

Figure 3. High-resolution data from the CSU/CHILL research radar shows the thunderstorm in Larimer County, CO, at 6:34 pm CDT on Thursday, June 5, as it was producing a tornado south of Berthoud. Top image is reflectivity (precipitation); bottom image is velocity (winds toward/away from the radar). The areas marked “reflectivity minimum” (top) and “radial velocity couplet” (bottom) coincide with the approximate location of the tornado. Image credit: Pat Kennedy, CSU/CHILL National Radar Facility. To see the westward development of the storm while the tornado was occurring, check out this loop of imagery from the NWS radar in Cheyenne, WY. The tornado developed near the Boulder/Larimer county line just north of Longmont (LMO on the radar loop). Image credit: NWS/CIRA.

Aside from last week’s tornado near Berthoud, the only other F3/EF3 tornado that moved west of I-25 in Colorado developed around noon on May 22, 2008--and it also had a westward component to its motion. This powerful twister, the most expensive in Colorado history, carved a wide, 39-mile-long path that extended to the north-northwest from near Platteville through the town of Windsor, damaging hundreds of homes there. A team led by Russ Schumacher and Dan Lindsey (Colorado State University) analyzed the event in 2010 in a paper for the journal Weather and Forecasting. Upper-level winds on that day were from the southeast, and instability was unusually strong for the region, which enabled the Windsor storm to develop as a fairly classic supercell, albeit with an unusual track and location. As for last week’s Berthoud storm, which had a much more pronounced westward motion, radar data indicates that it was in a “back-building” stage, growing quickly toward the west while the tornado itself was occurring (see Figure 3). “The westward motion appears to be driven by some combination of storm dynamics and low-level upslope flow,” says Schumacher. Lindsey summarizes the common thread between two events: “It seems to me that virtually the only way to get a real supercellular tornado west of I-25 is to have a storm moving with a component toward the west. And this one certainly qualifies.”

How can a tornado spin anticyclonically?
Social media has been abuzz over the last few days with spectacular images of an anticyclonic tornado near Simla, Colorado, northeast of Colorado Springs. Perhaps the most iconic photo was taken by accomplished photographer and storm chaser Kelly DeLay. Rather than going for a close-up, DeLay captured the entire storm in its full majesty--and the resulting image shows not just one but two twisters.

Figure 4. A supercell thunderstorm near Simla, Colorado, produced two tornadoes on June 4--one anticylonic (lower left) and one cyclonic (lower right). The thunderstorm itself was rotating cyclonically. Image credit: Kelly DeLay.

Anticyclonic tornadoes spin in a clockwise fashion, in contrast to most of their peers. Most supercells in the Northern Hemisphere rotate cyclonically (counterclockwise), as do the tornadoes they produce. This isn’t a direct result of the Coriolis force, a function of Earth’s rotation that causes hurricanes and other large low-pressure centers to spin cyclonically. Thunderstorms and tornadoes are too small to be dictated by the Coroilis force (and so are toilets!). Instead, the juxtaposition of winds at different heights tends to cause a supercell in the Northern Hemisphere to spin cyclonically, especially when it’s moving toward the right of the vertically averaged wind. Sometimes an anticyclonic tornado (usually fairly weak) will develop as a satellite twister on the fringe of a tornado-producing, cyclonically rotating supercell. This appears to be the process that drove the Simla tornado shown in Figure 4 above. There’s another way that an anticyclonic tornado can develop. If a supercell happens to move toward the left of the vertically averaged wind, rather than toward the right, it will spin in the other direction--anticyclonically--and it can thus produce an anticyclonic tornado. Several events like this have been documented in case studies, including a 1998 event in California and one in South Dakota in 2006.

For more background, including perspective from tornado researcher Josh Wurman, see this informative June 8 article by Angela Fritz at Capital Weather Gang.

Tropical Storm Carlos staying offshore of Mexico
Tropical Storm Carlos continues to churn in the Pacific Ocean, about 200 miles south of the Mexican coast. With very warm waters of 30°C (86°F) beneath it and wind shear a moderate 10 - 20 knots, Carlos appears destined to undergo slow intensification through Monday. Satellite loops and radar out of Acapulco shows that the outer spiral bands of Carlos have pushed onshore, but the storm's west-northwest motion, parallel to the coast, should keep the heaviest rains just offshore. Heavy rains of 3 - 6 inches will likely affect portions of the Mexican coast over the weekend, and if Carlos takes a path slightly closer to the coast than expected, dangerous flooding rains will occur. By Wednesday, Carlos may pose a threat to Mexico’s Baja Peninsula, but the cooler waters and more stable air the storm will encounter as it approaches Baja should cause Carlos to weaken below hurricane strength before a potential landfall there. We’ll have a full update on Carlos by Monday morning at the latest.

Have a great weekend, everyone!

Bob Henson and Jeff Masters

Video 1. The late Jim Leonard, a famed hurricane chaser, captured the first known video of a Northern Hemisphere anticyclonic tornado on June 6, 1975, near Freedom, Oklahoma. More details on this and other events can be found in Jim’s online biography. The embedded video above can also be viewed directly at YouTube.

Figure 5. A high-resolution GOES-14 image from around 6:00 pm CDT on Thursday, June 5, as intense supercells were raging across northeast Colorado. The Simla tornado emerged from the southernmost storm, while the Berthoud tornado was in the northermost storm in Colorado. In this animated satellite loop, crosshatch symbols show the approximate locations and occurrence times of the tornadoes. The images in the loop were collected every minute by GOES-14. Image/animation credit: Dan Lindsey, NOAA/CSU/Cooperative Institute for Research in the Atmosphere.

Severe Weather Tornado tropical cyclone

El Niño Continues to Ramp Up

By: Bob Henson , 8:31 PM GMT on June 11, 2015

The latest updates from NOAA (see PDF) and the Australian Bureau of Meteorology confirm that the El Niño event that began in earnest this spring continues to build. NOAA reports that sea-surface temperatures (SSTs) in the closely watched Niño3.4 region of the eastern tropical Pacific were 1.2°C above average last week, well into the range associated with moderate El Niño events (+1.0°C to +1.5°C). Based on another marker, the Multivariate ENSO Index, this El Niño event is already into the “strong” category. All of the Niño monitoring regions had SSTs of at least 1.2°C above average last week, making for the most widespread oceanic warmth since the landmark El Niño event of 1997–98. Policymakers and investors are already taking note of the potential implications of the intensifying El Niño for agriculture and the economy.

Figure 1. Sea-surface temperatures on June 8 show the hallmark of El Niño, with a band of warmer-than-average temperatures, extending along the equator across the central and eastern tropical Pacific and poleward near the South American coast. Two animations showing the emergence of this El Niño pattern can be found at Tom Yulsman’s ImaGeo blog (Discover Magazine). Image credit: NOAA/NESDIS.
Computer models are in firm agreement that El Niño conditions will strengthen further during the latter part of 2015. All eight of the international models tracked by BOM show Niño3.4 readings of 1.5°C or higher by October (see Figure 2), and several exceed 2.0°C, suggesting that the strongest event since 1997–98 may well be in the cards. Some models predicted that a significant El Niño would emerge in mid-2014, but that didn’t happen, largely because the atmosphere failed to respond to oceanic shifts that often kick off El Niño. This time, the atmosphere and ocean are much more in sync, so we can put more trust in the current model outlooks—especially now that we’re past the “spring predictability barrier” that makes early-year forecasts of El Niño so tough. In today’s update, NOAA is calling for a greater than 90% chance that El Niño will continue through the northern fall of 2015, and around an 85% chance it will last through the winter of 2015-16.

Figure 2. Projections of sea-surface temperature in the Niño 3.4 region (5°S - 5°N, 120°W - 170°W) for October 2015 in terms of departure from average (degrees C), as compiled from eight international climate models and released by the Australian Bureau of Meteorology in May. Each model’s projection on the graph above is based on the average of multiple runs in an ensemble. The threshold for El Niño conditions for Australia is 0.8°C above average, as shown on the chart, while the NOAA threshold (not shown) is 0.5°C. Image credit: BOM.
A wet footprint that’s already shown up
El Niño appears to have played a role in record-smashing rainfall over the south-central states last month, the main factor behind the single wettest month in U.S. history. Satellite imagery averaged for May shows a band of enhanced moisture sweeping from the Niño regions of the central and eastern tropical Pacific into the southern United States (see Figure 3). That upper-level moisture was pushed along by an strong subtropical jet stream and juxtaposed with unusually rich low-level moisture from the Gulf of Mexico. Kevin Trenberth (National Center for Atmospheric Research) sees a probable link between El Niño and the May rains. “It doesn't mean El Niño caused the pattern, but it did change the odds and helped it persist,” Trenberth told me. “Then the global warming component, whereby all SSTs are higher, adds to the moisture, and this is what helps break the records.”

Figure 3. Departures from the average amount of outgoing longwave radiation (OLR) for the period May 11 through June 9, 2015, as measured by satellite. Negative values denote outgoing radiation being blocked by clouds and precipitation. Strongly negative values (magenta) can be found over the central and eastern Pacific Ocean, where El Niño’s oceanic signature is based. An extension of low OLR values runs through Mexico into the western half of the United States. Image credit: NOAA Earth System Research Laboratory.
What will summer bring us?
On average, El Niño’s impacts on U.S. weather are much stronger in winter than in summer. As NOAA’s Anthony Barnston puts it in a recent ENSO Blog post, “while El Niño is the 800-pound gorilla in winter forecasts in the U.S., it is more like a tame, 6-pound Chihuahua in summer.” Barnston cites two reasons for this:
—El Niño affects climate in midlatitudes by adding energy to the Hadley circulation, a vast loop that sends tropical air upward and poleward and higher-latitude air downward and equatorward. The Hadley loop is weaker in the half of the world where summer is occurring, due to the reduced equator-to-pole temperature contrast. This means an El Niño event has less ability to torque climate in the summer hemisphere.
—Weaker north-south temperature gradients in summer also mean that the circulation patterns driving midlatitude weather are weaker and smaller-scale than they are in winter, again reducing the ability of El Niño to influence things.
The main tendency in U.S. weather during El Niño summers, albeit a weak one, is for above-average precipitation. In particular, the southwestern states may continue to see the effects of a Northeast Pacific hurricane season amped up by El Niño (which produces favorable atmospheric conditions in that basin) as well as by very warm SSTs. Already, remnant moisture from Hurricanes Andres and Blanca has led to periods of unusually high amounts of water vapor across the Southwest and bursts of rainfall that are uncommon in late spring for places like Phoenix, and today brought the birth of Tropical Storm Carlos (see this morning’s update from Jeff Masters. Meanwhile, in the Southern Hemisphere, El Niño will boost the odds of drought in Indonesia and parts of Australia over the next several months (see Figure 4). Toward the end of 2015, El Niño’s influence on U.S. climate should grow, and there’s a reasonable shot at a wetter-than-average winter in southern California, assuming that model forecasts of a strong El Niño prove accurate. For more on how the balance between the subtropical and polar jet streams is affected by El Niño events of various intensities, see this explainer by Daniel Swain at California Weather Blog.

Figure 4. Temperature and precipitation patterns that are typical of El Niño conditions during northern summer. Image credit:, based on originals from the NOAA Climate Prediction Center.
Looking further out: La Niña in 2016-17?
It’s far too early for dynamical models to peer beyond the current El Niño event, but if history is any guide, there’s a better-than-average chance of La Niña developing sometime in 2016. El Niño events usually last just one year—two at most—so the current event should be on the wane by early- to mid-2016, as suggested by the model guidance in Figure 2. When a significant El Niño pattern weakens, there can be a rebound effect that allows cooler-than-average water to upwell into the eastern tropical Pacific and revitalized trade winds to push it westward, leading to a La Niña event. NOAA’s historical database of Niño3.4 readings, which goes back to 1950, shows that most El Niño events of at least moderate strength were followed by La Niña conditions within a year of their demise. A classic example is the strong 1998-99 La Niña that quickly followed the powerful 1997-98 El Niño. That said, each El Niño event is different, and as every smart investor knows, past performance is no guarantee of future results. We’ll just have to wait and see if this El Niño—which took the better part of a year to get rolling—proves equally quirky on its way out the door.
Bob Henson

El Niño

Tropical Storm Carlos Forms South of Acapulco, Mexico

By: Jeff Masters , 3:29 PM GMT on June 11, 2015

Tropical Storm Carlos spun into life Thursday morning in the Pacific Ocean, about 230 miles south of Acapulco, Mexico. Satellite loops show that Carlos is a small storm in the early stages of organization. But with very warm waters of 30°C (86°F) beneath it and wind shear a moderate 10 - 20 knots, Carlos appears destined to intensify into a hurricane by the weekend. Radar out of Acaupulco shows that the outer spiral bands of Carlos lie just offshore from the Mexican coast, and the storm's west-northwest motion, parallel to the coast, should keep the heaviest rains just offshore. However, if Carlos takes a path slightly closer to the coast than expected, dangerous flooding rains will occur along the coast.

Figure 1. Tropical Depression Three-E south of Acapulco, Mexico as seen at 1:15 pm EDT June 10, 2015, before becoming Tropical Storm Carlos. Image credit: NASA.

Figure 2. Predicted total precipitation for Tropical Storm Carlos from the 06Z Thursday June 11, 2015 run of the HWRF model. Widespread areas of 4 - 8" were forecast just offshore from Mexico. Image credit: NOAA/NCEP/EMC.

An unusually early and severe Eastern Pacific hurricane season
Carlos' formation on June 11 continues a remarkable run of early-season activity for the Eastern Pacific. The third named storm usually does not appear until July 5, and Carlos' formation on June 11 comes just two days later than the record for the earliest appearance of the season's third named storm: June 9 in 1956 and 1990. Some other notable items from this year's Eastern Pacific hurricane season:

We've already had two major hurricanes this year (Andres and Blanca), and the second major hurricane of the season typically doesn't form until August 19. An entire season typically has only four major hurricanes (using stats from 1981-2010.) The record is eight major hurricanes in a season, accomplished most recently in 2014. Only six Northeast Pacific major hurricanes have occurred prior to June 5 since accurate satellite records began in 1971, and two of them were this year:

1) Hurricane Amanda, 2014: 155 mph winds on May 25
2) Hurricane Andres, 2015: 145 mph winds on June 1
2) Hurricane Adolph, 2001: 145 mph winds on May 29
4) Hurricane Blanca, 2015: 140 mph winds on June 3
5) Hurricane Alma, 2002: 115 mph winds on May 30
6) Hurricane Bud, 2012: 115 mph winds on May 25

- Hurricane Andres topped out as a Category 4 storm with 145 mph winds on June 1, becoming the second strongest Northeast Pacific hurricane for so early in the year.

- Blanca became a hurricane on June 2, setting a record for the earliest appearance of the season's second hurricane (previous record: Hurricane Boris of 1990 on June 5.) Blanca also set a record for the earliest appearance of the season's second major hurricane (June 3), and was the fourth strongest Northeast Pacific hurricane for so early in the year.

- Blanca made landfall on the west side of Mexico's Baja Peninsula on June 8, 2015, with top winds near 45 mph. Blanca's landfall came a month earlier than the previous earliest landfall on record for Baja (Tropical Storm Calvin on July 8, 1993.)

Wunderblogging hurricane expert Steve Gregory put up a Wednesday afternoon post looking at the tropics and long-range summer outlook for the U.S.; he plans to issue regular Atlantic hurricane updates twice per week.

Bob Henson will have an update on El Niño this afternoon.

Jeff Masters


The Climate 25: A Powerhouse Set of Interviews

By: Bob Henson , 3:00 PM GMT on June 10, 2015

What can you say about climate change in less than three minutes? Quite a bit, as it turns out. You can find out for yourself by sampling a group of thoughtful, provocative interviews being featured by The Weather Channel over the next month. Debuting today, “Climate 25” includes a stellar group of leaders from the military, academia, government, diplomacy, and other sectors of society. The executive producer of “Climate 25” is Solly Granatstein, whose work at “60 Minutes” earned George Polk, Edward R. Murrow, Gerald Loeb and Peabody Awards, as well as several Emmy Awards. At the end of this post, you’ll find the lineup of speakers, with links to each interview clip and the dates on which each clip will be spotlighted by TWC and

Figure 1. Eight of the eminent people featured in “Climate 25.”

On the Climate 25 website, TWC’s Neil Katz--editor in chief of the project--lays out the context:

“There are are only a few issues more contentious than climate change in American political life. But while the climate change debate rages in some quarters, in others, most notably among those who study the climate, there is wide consensus. It’s for this reason that The Weather Channel has adopted a position on climate change that can generally be summed up as follows: we report the science, and the science consistently says climate change is real, humans are causing it, and we must prepare for its effects. . . . These videos are the culmination of a year-long project looking at climate change as a real-world problem that will require creative solutions from all points on the political spectrum. We hope it encourages thoughtful debate and, more importantly, action on an issue that will affect us all.”

Climate change is a matter of enormous long-term consequence for the world as a whole. Too often, we have let the dialogue on how to address climate change become hijacked by “he said/she said” debates, non sequiturs, partisan rigidity, and other distractions. Much remains to be learned about the regional and local impacts of climate change over the coming decades and beyond, but we already know enough about the causes and potential consequences to begin adapting to change that’s on its way (and in some cases, here now) while reducing the risk of even greater change. The participants in Climate 25 have a great deal of wisdom to share on how we might go about these tasks, and why it’s so important to do so.

All of the Climate 25 mini-interviews are now viewable online at the links below. I strongly encourage you to check them out.

Bob Henson

June 10 | Thomas Friedman, New York Times
The revolution fueled by climate change

June 11 | Constance Okollet, Community Leader, Uganda
The floods swept my village away

June 12 | Henry Paulson, 74th U.S. Secretary of the Treasury
Doing nothing is “radical risk taking”

June 13 | Christine Todd Whitman, Former New Jersey Governor, EPA Administrator (2001-03)
We can grow the economy and fight climate change

June 14 | Gen. Charles E. Jacoby (Ret.), Commander, U.S. North Command
The biggest national security threat you haven’t thought of

June 15 | Paul Polman, CEO, Unilever
How CEO tackles Unilever’s $300M climate change challenge

June 16 | Heidi Cullen, Chief Scientist, Climate Central
This is what the perfect risk looks like

June 17 | Dr. John Holdren, Assistant to the President for Science and Technology
WH science advisor’s surprising view on why climate matters

June 18 | Cary Fowler, Special Advisor, Global Crop Diversity Trust
Extinction is a process, not an event

June 19 | Farah Nasif, Syrian Refugee
In Syria, everything changed with the drought

June 20 | Hal Harvey, CEO, Energy Innovation
Every decade we wait is a thousand years of pain we inflict on future generations

June 21 | Cleo Paskal, Author, “Global Warring”
The military crisis we’re not prepared for

June 22 | Major Gen. Munir Muniruzzaman (Ret.), Bangladesh
20% of Bangladesh could be lost to the sea

June 23 | Ursula Rakova, Community Leader, Papua New Guinea
Our islands are disappearing

June 24 | William K. Reilly, EPA Administrator (1983-93)
Bush EPA chief’s surprising view on climate change

June 25 | Rear Adm. David Titley (Ret.), Former Naval Oceanography Operations Command
The nation’s defense is at stake

June 26 | Bob Inglis, Former U.S. Representative (R–S.C.)
The Republican orthodoxy is changing

June 27 | Sherri Goodman, U.S. Deputy Undersecretary of Defense (1993-2001)
Climate change is a threat multiplier

June 28 | Eli Lehrer, President, R Street Institute
Climate change real? Ask the guys who could lose billions

June 29 | Brig. Gen. Stephen Cheney, USMC (Ret.), CEO, American Security Council
70% of the world’s military is preparing for climate change

June 30 | Joe Romm, Founding Editor, Climate Progress
We can save the world from hundreds of years of misery

July 1 | Helene Gayle, President and CEO, CARE USA (2006-15)
What you don’t know about the world’s biggest threat to food security

July 2 | Nicky Sundt, WWF, Former Wildland Firefighter
There’s no escape route when it comes to climate change

July 3 | James Woolsey, Director of Central Intelligence (1993-95)
Former CIA director’s surprising take on climate change and national security

July 4 | George Luber, Associate Director for Climate Change, CDC
Why climate change has CDC scientists worried

Climate Change

May 2015: All-Time Wettest Month on Record for the U.S.

By: Bob Henson , 11:16 AM GMT on June 09, 2015

It wasn’t a soggy May for the whole country, but where it did rain last month, it poured--enough to give the 48 U.S. states as a whole their wettest single month since records began in 1895, according to the monthly report from NOAA’s National Centers for Environmental Information (formerly called the NCDC). With a 48-state average of 4.36”, last month beat out the 4.28” observed in June 1928 and the 4.24” from May 1957. The main reason for the record was the unusually prolonged and intense sequence of heavy thunderstorms centered on the south-central states, a spell that conveniently extended from just a couple of days after the first of May until right before the month ended. Colorado had its wettest May on record, while Texas and Oklahoma had their wettest single month since records began. For a large swath of the country, from the southern Great Basin throughout the Great Plains, this month ranked among the ten wettest Mays on record (see Figure 2).

Figure 1. Motorists commute across Interstate 30 (right) over a swollen Trinity River west of downtown Dallas on May 29, as weeks of torrential rain were drawing to a close. Image credit: AP Photo/Brandon Wade.

Despite the Plains deluge, many of the nation’s biggest population centers were actually on the dry side. Eastern states got the short end of the precipitation stick last month, with much-below-average rainfall from the Appalachians to the coastline. Six states had a top-ten dry May: South Carolina, Delaware, New Jersey, Connecticut, Rhode Island, and Massachusetts. Since there is little irrigation in this part of the country, it only takes three or four weeks of scant rainfall to begin causing problems for agriculture and ecosystems. Fortunately, a series of wet frontal systems over the last few days has put a dent in this short-term dry spell. For the nation as a whole, May was a colossal drought-buster. The fraction of the contiguous U.S. categorized as being in drought by the weekly U.S. Drought Monitor plummeted from 37.4% in late April to 24.6% on June 2, hitting its lowest percentage since February 2011.

Figure 2. Precipitation (top) and temperature (bottom) rankings for May 2015 in each of the 48 contiguous U.S. states. In the top image, a value of 121 denotes the wettest May in records that go back to 1895, while 1 indicates the driest. For the bottom image, 121 corresponds to the hottest May on record, and 1 denotes the coolest. Image credit: NOAA National Centers for Environmental Information.

Temperatures for the month largely reflected where it was persistently wet or dry. Frequent clouds and storms blocked enough late-spring sunlight to bring the monthly temperature well below average from Arizona, New Mexico, and Texas to Wyoming and South Dakota. For the East Coast, and especially the Northeast, it was weather whiplash, temperature-style. Not long after each state saw its second-coldest February on record, the residents of New Hampshire, Massachusetts, Connecticut, and Rhode Island all sailed into their warmest May in more than a century of record keeping. Seven other adjoining states had a top-ten warmest May, as did Florida and Washington state. It was also the warmest May on record in Alaska--a full degree beyond than the previous record-holder, May 2005.

Even with temperatures now in the 70s and 80s, people in the Boston area have a stubborn, unsightly reminder of winter: several enormous piles of trash-bearing snow that are proving excruciatingly slow to get rid of. The multiple reasons for the leisurely melt are nicely outlined in this Boston Globe article. The snow/trash pile at the Seaport District was still three stories tall as of late May, and it may take until July to completely disappear.

Figure 3. Canada geese swim beneath a debris-covered snow pile on May 28 in Boston’s Seaport District. A snow mound that once towered 75 feet high was by this point a three-story pile of dirt and trash, including bicycles, traffic cones and even half a $5 bill, that remains encrusted in solid ice. Crews have been working for weeks to clean away the trash as it breaks free from the mound. As of late May, they had pulled 85 tons of debris from the pile. Image credit: AP Photo/Elise Amendola.

El Niño making its presence known
The El Niño event that’s been steadily strengthening in recent weeks likely played a key role in fostering the downpours across the south-central U.S. As the event brings warmer-than-average waters over the eastern tropical Pacific Ocean, showers and thunderstorms moves eastward as well. This change in atmospheric circulation triggers a chain of reverberating effects, typically bringing wetter-than-usual conditions to the southern U.S. and drier-than-usual weather across parts of the northern tier of states. Part of the adjustment involves a strengthening of the subtropical jet stream, which was unusually strong across Mexico and the southwest U.S. last month. At the California Weather Blog, Daniel Swain provides an excellent description of how the balance between the subtropical and polar jet streams is affected by El Niño events of various intensities. If the current event remains potent, it substantially raises the odds of at least some drought relief for California this fall and winter. Another factor in the storminess across the central states during May was moisture-rich low-level air coursing from the Caribbean through the Gulf of Mexico and into Texas. Warm sea-surface temperatures helped boost the moisture content in this persistent surface flow.

Figure 4. Observed decadal rate of change in global annual precipitation over land areas, 1951 - 2010. The cumulative change in annual precipitation at any spot, in mm/yr, can be calculated by multiplying the value shown by 6 (for six decades]. Dots represent areas where the change is significant, including the central United States. Areas in white either have little or no trend, or too little data to calculate a robust estimate. Image credit: IPCC AR5 Synthesis Report, Figure 1.1, page 41 (PDF link).

Record-wet month is in line with a warming climate
The sodden swath across the Great Plains last month is intriguingly similar to what shows up in annual precipitation trends over the last 50 years, as analyzed by the Intergovernmental Panel on Climate Change, or IPCC, in its most recent synthesis report (see Figure 4). Although it’s a challenge to measure on a global scale, the average annual precipitation for the entire planet appears to be on the increase, and the 48-state U.S. average has increased from just over 29” per year in the late 1890s to nearly 31” today (see Figure 5). Droughts are still with us, of course—and drought impacts are greatly exacerbated by hotter temperatures—but at the same time, wet periods are increasingly wetter, as more water vapor enters the atmosphere from steadily warming oceans. Not all of the world is getting wetter, though. IPCC projections for the late 21st century, based on multiple climate models, show that much of the global increase in precipitation will occur at middle and higher latitudes, with subtropical areas tending to dry out, a pattern already showing up in recent years. Grinding drought has plagued the Southwest U.S. for much of the last 15 years, a period that corresponds to a predominantly negative phase of the Pacific Decadal Oscillation. Now that the PDO has shifted into a positive phase, which tends to favor El Niño, it will be interesting to see if the Southwest--including California--manages to get a few years of rainfall more in line with the 20th-century average. Even if it does, the region still has major challenges ahead, as warming temperatures and increasing populations will add to the impact when drought does, inevitably, recur.

Bob Henson

Figure 5. Average precipitation for the contiguous 48 U.S. states, 1895 - 2014. The annual average increased by about 5% during the 20th century. Image credit: NOAA National Centers for Environmental Information.

Climate Summaries Climate Change Flood

India's 2nd Deadliest Heat Wave in History Ends as the Monsoon Arrives

By: JeffMasters, 6:38 PM GMT on June 08, 2015

The monsoon has arrived in India. The India Meteorological Department (IMD) announced that the monsoon arrived on Friday, June 5 at the southern tip of the country--four days later than the usual June 1 arrival. Although the monsoonal rains have not yet reached the province hardest hit by the heat wave--Andhra Prahesh in Southeast India--the atmospheric circulation associated with the monsoon has caused temperatures to drop significantly in this region in recent days, ending the heat wave. India's deadly May 2015 heat wave claimed approximately 2,500 lives, ranking as the second deadliest heat wave in India's recorded history--and the fifth deadliest in world history. According to statistics from EM-DAT, the International Disaster Database, India's only deadlier heat wave was in 1998, when 2,541 died. Below is the list of top ten deadliest heat waves in world history as compiled by EM-DAT (which uses direct deaths for their statistics, and not excess mortality):

The 10 Deadliest Heat Waves in World History
1) Europe, 2003: 71,310
2) Russia, 2010: 55,736
3) Europe, 2006: 3,418
4) India, 1998: 2,541
5) India, 2015: 2,500
6) U.S. and Canada, 1936: 1,693
7) U.S., 1980: 1,260
8) India, 2003: 1,210
9) India, 2002: 1,030
9) Greece and Turkey, 1987: 1,030

Figure 1. Temperatures in Machilipatnam, Andhra Prahesh, India from May 14 - June 8, 2015 show that the heat wave peaked between May 22 - May 26, with high temperatures rising as high as 118°F (47.8°C.)

Death toll from the 2015 India heat wave questioned
As I discussed in more detail in my May 29 post on the heat wave, death tolls from heat waves are very difficult to estimate, since excess heat is typically just one factor contributing to a death. For example, the U.S. National Climatic Data Center (NCDC) lists the total direct deaths from the U.S. heat wave of 1980 at 1,260, but estimates that the combined direct and indirect deaths (i.e., excess mortality) due to heat stress was 10,000. According to an article in The Indian Express, the death toll from this year's heat wave in India may be much lower than 2,500. Of the 1,636 heat wave deaths reported between May 15 and May 30 in the hardest-hit province of Andhra Pradesh, only 511 were certified to have been caused by heat; the number of reported heat deaths soared when officials offered monetary compensation to relatives of heat victims. "The number of deaths being reported to mandal officers, Andhra Disaster Management Authority officials say, almost doubled after Chief Minister N Chandrababu Naidu announced ex-gratia of Rs 1 lakh to the kin of each person who dies in the heat wave," The Indian Express reported. However, even if the number of deaths in the heat wave were 1,000 less than officially reported, it still would rank as the second deadliest in India's history, and seventh deadliest in world history.

Figure 2. Progress of the monsoon towards India as of June 8, 2015 (green line) has lagged by about 4 - 9 days compared to its usual pace. The province hardest hit by this year's heat wave, Andhra Prahesh (shaded in yellow), should see the monsoon move through late this week and early next week. The province recorded 1,735 heat deaths as of June 3, 2015. Image credit: India Meteorological Department .

A deficient monsoon predicted
Although the heat wave of 2015 has ended, India's weather troubles are not over this year. The problem: the atmospheric circulation patterns brought on by an El Niño event usually cause much reduced monsoon rains. The current moderate El Niño event is forecast to intensify this summer, and this is likely to cause a significant reduction in monsoon rainfall over India. IMD is forecasting only a 7% chance of near-average rains during the 2015 summer monsoon period, and a 93% chance of below average or well below average rains. IMD's best estimate is that 12% less rain than usual fall, which would cause severe stress on agriculture and the power grid, which relies heavily on hydroelectric power. However, a 12% reduction in rains would not rank in the top five for worst monsoons on record. The five worst Indian monsoons for rainfall deficit were:

1) 1877, -33%
2) 1899, -29%
3) 1918, -25%
4) 1972, -24%
5) 2009, -22%

Climate change and India
This year's deadly heat wave in India was made much more probable by the fact that Earth is experiencing its hottest temperatures on record--the past twelve months were the warmest twelve-month period in recorded history, and so was the January - April 2015 period. According to the India Meteorological Department, a warming climate increased heat waves in India by a third between 1961 to 2010. As the planet continues to warm due to human-caused global warming, heat waves will become more frequent and more intense, and heat-related deaths will soar unless we take strong measures to adapt. An April 2015 paper published in Regional Environmental Change, Intensification of future severe heat waves in India and their effect on heat stress and mortality, warned that "heat waves are projected to be more intense, have longer durations and occur at a higher frequency and earlier in the year. Southern India, currently not influenced by heat waves, is expected to be severely affected by the end of the twenty-first century." Perhaps a bigger concern for India with climate change is drought, though. Many climate models show that climate change might increase the average rainfall in India from the monsoon, but when dry years occur, the hotter temperatures accompanying the dry years will drive much more intense droughts capable of causing significant challenges to growing food in India.

Figure 3. Tropical Cyclone Ashobaa as seen from the International Space Station at 3 pm EDT Sunday June 7, 2015. At the time, the storm had top winds of 45 mph. Image credit: Terry Virts.

Tropical Cyclone Ashobaa forms in the Arabian Sea
The ocean regions surrounding India have two tropical cyclone seasons, one from May to early June before the monsoon arrives, and one beginning in late October after the monsoon departs. During the June - October peak of the monsoon season, the monsoon dominates the atmospheric circulation in the Bay of Bengal and Arabian Sea, and only rarely allows a tropical cyclone to form. The only tropical cyclone so far this year in the North Indian Ocean, Tropical Cyclone Ashobaa, formed on Sunday just north of the advancing monsoon in the waters of the Arabian Sea to the west of India. Ashobaa is predicted to attain Category 1 strength before hitting cooler water and dryer air this weekend, which should weaken it to a tropical storm.

Jeff Masters


Tropical Storm Blanca Hits Baja a Month Earlier Than Their Previous Earliest Landfall

By: Jeff Masters , 1:43 PM GMT on June 08, 2015

Tropical Storm Blanca made landfall on the west side of Mexico's Baja Peninsula near 8 am EDT Monday June 8, 2015, with top winds near 45 mph. Blanca's landfall comes a month earlier than the previous earliest landfall on record for Baja, a strike by Tropical Storm Calvin on July 8, 1993. Calvin made landfall south of La Paz with sustained winds of 45 mph. Satellite loops show that Blanca's heavy thunderstorms are pushing northwards over the Baja Peninsula and into Mainland Mexico, and rainfall amounts of 3 - 5 inches can be expected in these areas through Monday. Moisture from Blanca will flow into Southern California, Arizona, and New Mexico beginning on Tuesday, bringing localized rains of 1 - 2 inches. Blanca brought top sustained winds of 34 mph to Los Cabos Airport on the southern tip of the Baja Peninsula Sunday night.

Figure 1. Tropical Storm Blanca as seen by the MODIS instrument on NASA's Terra satellite at 2:30 pm EDT Sunday June 7, 2015. At the time, Blanca was weakening from a Catgeory 1 hurricane with 90 mph winds to a tropical storm with 70 mph winds. Image credit: NASA.

Figure 2. Hurricane Blanca sat in place for three days, intensifying from a tropical storm to a Category 4 hurricane with 140 mph winds. Blanca's strong winds were able to stir up cool waters from the depths that cooled the oceans surface temperature a remarkable 9°C (16°F)--from 30°C (86°F) to 21°C (70°F.) This is one of the most intense cold wakes left by a hurricane that I've seen. Image credit: NOAA/AOML.

New Northeast Pacific disturbance 94E may develop near Mexican coast
An area of low pressure (Invest 94E) has formed in the Pacific a few hundred miles south of Mexico's Gulf of Tehauntepec, and has the potential to develop into a tropical depression. Wind shear is a low 5 - 10 knots and SSTs are a very warm 30°C (86°F), but satellite loops show 94E does not yet have much organization of its heavy thunderstorms. The 00Z Monday run of the European model and 06Z run of the GFS model predicted that 94E would develop into a tropical depression by Thursday and begin bringing heavy rains to the southeast coast of Mexico that day. A motion west-northwest parallel and just offshore was predicted, which would make 94E a dangerous heavy rain threat for the coast. In their 8 am EDT Monday tropical weather outlook, NHC gave 2-day and 5-day odds of development of 30% and 80%, respectively. It is possible that moisture from this disturbance could flow northwards into the southwest Gulf of Mexico's Bay of Campeche early next week, boosting the chances of a tropical disturbance capable of forming into a tropical depression there.

To follow this year's action in the tropics, I recommend the Twitter feed of NHC hurricane specialist Eric Blake.

Jeff Masters


Category 1 Hurricane Blanca Losing Strength as it Heads Towards Baja Mexico

By: JeffMasters, 3:18 PM GMT on June 07, 2015

Hurricane Blanca, a Category 1 storm with 90 mph winds at 11 am EDT Sunday, is steadily losing strength as it heads north-northwest at 12 mph towards Mexico's Baja Peninsula. Satellite loops show that Blanca has lost its eye, and the cloud pattern has assumed an elongated oval shape in the face of wind shear that has risen to a moderately high 15 - 20 knots. Cooler waters and a drier surrounding air mass should continue to cause steady weakening, and Blanca should be a weak tropical storm when it makes landfall in Mexico's Baja Peninsula on Monday. Cabo San Lucas on the southern tip of the Baja Peninsula will likely see winds no stronger than 50 mph as Blanca makes its closest approach, and heavy rain rains will be the main threat to Mexico's Baja Peninsula from Blanca. Moisture from Blanca will flow into Southern California, Arizona, and New Mexico beginning on Tuesday, bringing localized rains of 1 - 2 inches. An Air Force hurricane hunter aircraft will investigate Blanca on Sunday afternoon.

Figure 1. Hurricane Blanca as seen on June 5, 2015 from the International Space Station. Image credit: Terry Virts.

Figure 2. Predicted total precipitation from the 06Z Sunday run of the GFDL model. Widespread areas of 2 -4" were forecast along the Baja Peninsula. Image credit: NOAA/GFDL.

Record-early tropical-storm impacts possible in Baja California
Should Blanca deliver winds of tropical-storm strength to Baja California, it would be the earliest such occurrence since the beginning of modern tropical cyclone records for the Northeast Pacific in 1949. Between 1949 - 2014, only two tropical cyclones have made it within 100 miles of Baja California prior to July. One of these was a tropical depression in 1993 that slid north along the eastern coast of the peninsula, dissipating just east of La Paz. The other was a hurricane that cut just south of the peninsula at minimal Category 1 strength on June 14, 1958. The earliest named storm to hit Baja was Tropical Storm Calvin of 1993, which made landfall south of La Paz on July 8 as a weak tropical storm with 45 mph winds. This year looks set to carve many more marks in the history of Northeast Pacific tropical cyclones, given the unusually warm SSTs that prevail as well as the continued strengthening of El Niño, which favors hurricane development in this basin.

Figure 3. Tropical cyclones observed between January and June since modern records began in the Northeast Pacific (1949). Image credit: NOAA Historical Hurricane Tracks.

New Northeast Pacific disturbance may develop near Mexican coast
An area of low pressure has formed in the Pacific a few hundred miles southwest of Mexico/Guatemala border, and has the potential to develop into a tropical depression late this week. The 00Z Sunday run of the European and UKMET models predicted that this disturbance would develop into a tropical depression by Friday and begin bringing heavy rains to the southeast coast of Mexico by Thursday. The Sunday morning runs of the GFS model did not show the disturbance developing. In their 8 am EDT Sunday tropical weather outlook, NHC gave 2-day and 5-day odds of development of 10% and 60%, respectively. It is possible that moisture from this disturbance could flow northwards into the southwest Gulf of Mexico's Bay of Campeche early next week, boosting the chances of a tropical disturbance capable of forming into a tropical depression there.

Live streaming camera on the very southern tip of Baja California.

Another camera is just east of this one, on the Bay (Bahia) of San Lucas at Sunset Da Monalisa.

Jeff Masters and Bob Henson


Hurricane Blanca Regains Category 4 Status

By: Bob Henson , 4:23 PM GMT on June 06, 2015

Hurricane Blanca has accomplished the rare feat of reaching Category 4 status on the Saffir-Simpson scale for a second time after weakening to Category 1 level in between. Blanca continued plowing northwestward parallel to the Mexican coastline on Saturday morning after a dramatic burst of intensification overnight pushed its sustained winds to 130 mph, as of the 9:00 am MDT advisory from the National Hurricane Center. Earlier in the week, Blanca rapidly strengthened from a tropical storm on Tuesday morning to Category 4 strength on Wednesday, then suddenly weakened to a 110-mph storm in only 12 hours and fell to a Category 1 intensity on Friday afternoon (90 mph) before getting its second wind on Friday night. With peak winds of 140 mph on June 3, Blanca was the fourth strongest Northeast Pacific hurricane for so early in the year. Blanca’s slow forward motion enabled its rapid midweek intensification, as the hurricane parked over a hot spot of deep, warm water, but the slow pace also enabled Blanca to churn up enough cold water to help cause its rapid weakening.

Figure 1. Hurricane Blanca as seen by the MODIS instrument on Saturday afternoon, June 6, 2015. At the time, Blanca was a Category 3 storm with 120 mph winds. Image credit: NASA Worldview.

Record-early tropical-storm impacts possible in Baja California
Blanca will continue to benefit from sea-surface temperatures that are more than 2°C above average along its path, with waters at the southern tip of Baja California already close to 26°C. As Blanca proceeds north of that point, its fate will be sealed by increasingly cool sea-surface temperatures. However, the storm could yet make history before running aground on the mountains of Baja California on Monday. The latest track forecast from the National Hurricane Center, issued at 9:00 am MDT Saturday, brings Blanca onto the west coast of Baja California near Puerto San Carlos as a tropical storm. Because of its nearly parallel track to the coast, Blanca could make landfall considerably north or south of that point. Regardless, Blanca appears likely to bring tropical-storm-force winds to the southernmost part of the peninsula from late Sunday into early Monday. A hurricane watch is in effect from Cabo San Lucas to Santa Fe, with a tropical storm warning from La Paz to Santa Fe, including Cabo San Lucas. Tropical storm watches have been hoisted northward of La Paz to San Evaristo and from Santa Fe to Cabo San Lazaro.

Should Blanca deliver winds of tropical-storm strength to Baja California, it would be the earliest such occurrence since the beginning of modern tropical cyclone records for the Northeast Pacific in 1949. In fact, during that period, only two tropical cyclones have made it within 100 miles of Baja California during the first half of the year (see Figure 2 below). One of these was a tropical depression in 1993 that slid north along the eastern coast of the peninsula, dissipating just east of La Paz. The other was a hurricane that cut just south of the peninsula at minimal Category 1 strength on June 14, 1958. This year looks set to carve many more marks in the history of Northeast Pacific tropical cyclones, given the unusually warm SSTs that prevail as well as the continued strengthening of El Niño, which favors hurricane development in this basin.

Figure 2. Tropical cyclones observed between January and June since modern records began in the Northeast Pacific (1949). Image credit: NOAA Historical Hurricane Tracks.

A splash of rain at a dry time of the year for Arizona
Blanca’s remnants are expected to bring potentially heavy rain to parts of northwest Mexico early next week, with moisture and rains moving into Arizona, Utah, and neighboring states by midweek (see Figure 4 below). However, the active Northeast Pacific is already affecting rainfall over the southwestern United States. Moisture from the remnants of Hurricane Andres has combined with an unseasonably strong upper low over southern California to spark showers and thunderstorms well ahead of the usual monsoon rains of summer. Winds estimated at 60 mph struck near Gilbert, AZ, on Thursday, and hail up to tennis ball size was reported in Coconino County, Arizona, on Friday. Phoenix set a daily rainfall record on Friday with 0.16”, the city’s first measurable rain on that date since records began in 1896. That leaves June 11 as the only calendar date of the year in which Phoenix has never reported measurable rain (although a trace fell on that date in 1991).

Live streaming camera on the very southern tip of Baja California.
Another camera is just east of this one, on the Bay (Bahia) of San Lucas at Sunset Da Monalisa.

Jeff Masters will have an update on Blanca by Monday.

Bob Henson

Figure 3. Category 2 Hurricane Blanca (right) and the remnants of Tropical Storm Andres (left) as seen by the VIIRS instrument on the Suomi spacecraft on June 5, 2015. Image credit: NASA Worldview.

Figure 4. Predicted total precipitation from the 06Z Saturday run of the GFDL model. Areas of 4 - 8" (dark green colors) were forecast along the Baja Peninsula, over Mainland Mexico south of the Arizona border, and in Central Arizona. Image credit: NOAA/GFDL.


Category 2 Hurricane Blanca Headed Towards Baja Mexico

By: JeffMasters, 3:17 PM GMT on June 05, 2015

Hurricane Blanca off the Pacific coast of Mexico has changed little since Thursday morning, when the storm weakened significantly from Category 4 strength to a Category 2 storm with 100 mph winds, thanks to cooler waters from the depths that were churned up by the hurricane's powerful winds. The eyewall completely collapsed on Thursday, and satellite loops show that Blanca is struggling to rebuild a new eyewall in the face of wind shear that has risen to the moderate level, 10 - 20 knots. Late Friday morning, infrared satellite images showed that the intensity and areal coverage of Blanca's heavy thunderstorms had increased markedly, though, and it is likely that the Air Force Hurricane Hunters will find an intensifying hurricane when they investigate the storm on Friday afternoon. Blanca will be over warm waters until Saturday afternoon, when it will hit cooler waters and a drier surrounding air mass. These conditions should lead to gradual weakening, and Blanca should be below hurricane strength when it makes landfall in Mexico's Baja Peninsula on Sunday night or Monday. Blanca will pose a heavy rainfall threat to Mexico's Baja Peninsula beginning on Sunday. Moisture from Blanca will flow into Arizona and New Mexico beginning on Tuesday, bringing localized rains of up to one inch.

Figure 1. Category 2 Hurricane Blanca (right) and a dissipating Tropical Storm Andres (left) as seen by the VIIRS instrument on the Suomi spacecraft on June 4, 2015. Moisture from Andres can be seen flowing across the Mexico's Baja Peninsula into Arizona. Image credit: NASA Worldview.

Figure 2. Predicted total precipitation from the 06Z Friday June 5, 2015 run of the GFDL model. Some areas of 4 - 8" were predicted for the southern Baja Peninsula and Mainland Mexico south of the Arizona border. Image credit: NOAA/GFDL.

The last hurricane in Baja: destructive Hurricane Odile of 2014
While Blanca's rains may cause some flooding problems on Mexico's Baja Peninsula, Blanca's impact on Baja will be nothing like last year's Hurricane Odile, which roared ashore near Cabo San Lucas as a Category 3 storm with 125 mph winds on September 25. Odile was the strongest storm on record to hit Baja, and killed eleven and did $1.22 billion in damage, making it the 6th most expensive Northeast Pacific hurricane ever. The name "Odile" was retired from the list of Northeast Pacific hurricanes, and will be replaced by "Odalys", which will appear on the list of names for the 2020 season. Odile is one of only thirteen hurricanes in the Northeast Pacific to get its name retired since naming began in 1960.

Figure 3. MODIS satellite image of Hurricane Odile approaching the tip of Mexico's Baja Peninsula, taken at approximately 4:30 pm EDT Sunday September 14, 2014. At the time, Odile was a Category 3 storm with 125 mph winds. Image credit: NASA.

Remnants of Andres bringing rain to Arizona
Hurricane Andres dissipated over the cool waters off the Baja coast of Mexico on Thursday, but moisture from the storm's remnants has sloshed into the Southwest, bringing Phoenix, Arizona its first measurable rain ever recorded on June 5th. A thunderstorm around 7 am local time Friday brought 0.02" to the city. Weather records in Phoenix go back to 1896. Early June is usually a dry time in Central Arizona, since the cold fronts of spring do not push that far south, and the summer monsoon season usually holds off until early July. That's when summer heat builds to the point where the deserts create enough rising hot air to suck in moist air from the ocean areas to the south to replace the rising air, bringing spectacular thunderstorms.

New Northeast Pacific disturbance may develop near Mexican coast
The GFS and European models are predicting the formation of an area of low pressure area early next week a few hundred miles south or south-southeast of Mexico's Gulf of Tehuantepec. The 00Z Friday run of the European model predicted that this disturbance would develop into a tropical depression by Wednesday and begin bringing heavy rains to the coast of Mexico just west of Guatemala on Wednesday and Thursday. The Friday morning runs of the GFS model did not show the disturbance developing. In their 2 pm EDT Friday tropical weather outlook, NHC gave 2-day and 5-day odds of development of 0% and 30%, respectively.

Live streaming camera on the very southern tip of Baja California.
Another camera is just east of this one, on the Bay (Bahia) of San Lucas at Sunset Da Monalisa.

Jeff Masters


Hurricanes Blanca and Andres Set Records For Early-Season Northeast Pacific Activity

By: Jeff Masters , 3:38 PM GMT on June 04, 2015

Hurricane Blanca put on a furious display of rapid intensification this week, going from a tropical storm with 70 mph winds on Tuesday morning to a Category 4 storm with 135 mph winds on Wednesday morning--a remarkable 65 mph increase in winds in 24 hours, an intensification rate that is rarely seen. Blanca topped out at 140 mph winds on Wednesday afternoon, making it the fourth strongest Northeast Pacific hurricane for so early in the year. It has been a remarkable run of early-season activity for the region, since just two days before that Hurricane Andres topped out as a Category 4 storm with 145 mph winds, becoming the second strongest Northeast Pacific hurricane for so early in the year. Only six Northeast Pacific major hurricanes have occurred prior to June 5 since accurate satellite records began in 1971, and two of them were this year:

1) Hurricane Amanda, 2014: 155 mph winds on May 25
2) Hurricane Andres, 2015: 145 mph winds on June 1
2) Hurricane Adolph, 2001: 145 mph winds on May 29
4) Hurricane Blanca, 2015: 140 mph winds on June 3
5) Hurricane Alma, 2002: 115 mph winds on May 30
6) Hurricane Bud, 2012: 115 mph winds on May 25

Figure 1. VIIRS infrared image of Hurricane Blanca taken at 3:58 pm EDT June 3, 2015. At the time, Blanca was at peak strength, with top winds of 140 mph. Image credit: Dan Lindsey, NOAA/RAMMB/CIRA.

Figure 2. The eye of Hurricane Andres as seen at dawn on June 1, 2015 from the International Space Station. At the time, Andres was a Category 4 storm with 140 mph winds. Image credit: Terry Virts.

Blanca became a hurricane on June 2, setting a record for the earliest appearance of the season's second hurricane, beating the previous record set by Hurricane Boris of 1990 on June 5. Blanca also set a record for the earliest appearance of the season's second major hurricane on June 3. This is the second year in a row that the Eastern Pacific has set a record for the earliest appearance of the season's second major hurricane. The previous record was set June 12, 2014 (Hurricane Christina.) Only one other season besides 2015 has had the first two storms of the season intensify into major hurricanes--1995, when the year kicked off with Hurricane Adolph and Hurricane Barbara. The second major hurricane of the season typically doesn't form until August 19, and an entire season typically has only four major hurricanes (using stats from 1981-2010.) The record is eight major hurricanes in a season, accomplished most recently in 2014 (with a ninth storm, Genevieve, becoming a major hurricane after it crossed over into the Central Pacific.)

Forecast for Blanca
Hurricane Blanca performed its rapid intensification feat while parked for three days over an ocean hot spot, with warm waters of at least 26°C (79°F) that extended to a depth of about 100 meters (328 feet.) However, the storm sat too long in one place, and the powerful winds of the storm were finally able to churn up cooler waters from the depths on Thursday morning, causing Blanca to weaken to a Category 2 storm with 110 mph winds (though an eyewall replacement cycle also may have contributed to the weakening.) Satellite loops show that a portion of the eyewall collapsed, and the cloud tops have warmed, indicating that the heavy thunderstorms of the hurricane have weaker updrafts and no longer extend as high into the sky. The storm began a slow motion to the northwest at 3 mph on Thursday morning, though, and this motion will carry the storm away from the cold spot it created, and should allow Blanca to re-intensify. By Friday, the hurricane should be at Category 2 strength, but is unlikely to have enough time to become a Category 4 or 5 storm before hitting cooler waters and a drier surrounding air mass on Saturday. An Air Force hurricane hunter aircraft is scheduled to investigate Blanca on Friday afternoon. Blanca will pose a heavy rainfall threat to Mexico's Baja Peninsula beginning on Sunday.

The earliest Category 5 storm in the Northeast Pacific was Hurricane Ava of 1973, which peaked at 160 mph winds on June 6, 1973. The earliest Category 5 storm in the Atlantic occurred on July 16, 2005, when Hurricane Emily attained sustained winds of 160 mph.

Figure 3. The total heat content of the ocean at 2 am EDT June 4, 2015 showed that Hurricane Blanca has been sitting over a "hot spot" for heat energy over the past three days. For hurricanes with intensities less than 90 mph in favorable environmental conditions for intensification (vertical wind shear less than 15 kt, mid-level relative humidity >50 %, and warm SSTs >28.5°C), values of ocean heat content greater than 50 kJ/cm^2 (yellow colors) have been shown to promote greater rates of intensification. Image credit: NOAA/CIRA/RAMMB.

NOAA and CONAGUA predict an active Northeast Pacific hurricane season
Andres and Blanca are merely the opening salvos of what is likely to be a very busy Northeast Pacific hurricane season. Averaged over the entire Northeast Pacific, sea surface temperatures are running 1°C (1.8°F) above average, which is an unusually high amount of extra heat energy available for storms to take advantage of. NOAA's pre-season prediction for the Eastern Pacific hurricane season, issued on May 27, calls for 15 - 22 named storms, 7 - 12 hurricanes, 5 - 8 major hurricanes, and an ACE index 110% - 190% of the median. The mid-point of these ranges gives us a forecast for 18.5 named storms, 9.5 hurricanes, and 6.5 major hurricanes, with an ACE index 150% of average. CONAGUA, the Mexican meteorological service, is predicting 19 named storms, 8 hurricanes, and 4 intense hurricanes. The 1981 - 2010 averages are 15 named storms, 8 hurricanes, and 4 major hurricanes.

Wunderblogging hurricane expert Steve Gregory will begin issuing regular Atlantic hurricane updates twice per week, beginning Thursday, June 4.

Jeff Masters


Yangtze Cruise-Ship Disaster: Among the Worst Thunderstorm Tolls on Record?

By: Bob Henson , 3:42 PM GMT on June 03, 2015

A picturesque vacation for hundreds of Chinese tourists turned into a nightmare on June 1, when high winds associated with an intense thunderstorm capsized the Oriental Star cruise ship in 50-foot-deep water on the Yangtze River in Hubei Province, southwest of Wuhan, at around 9:30 pm local time. As of Tuesday afternoon, only 14 people had been rescued from about 450 reportedly on board, most of them retirees on a multiday scenic cruise from Nanjing to Chongqing. The disaster appears set to become China’s deadliest ship-related accident in almost 70 years. It’s unclear whether the cruise ship was sunk by a tornado or by a microburst, but in either event, the death toll could end up among the largest on record associated with a single thunderstorm. A 2011 post by WU weather historian Christopher Burt showed less than 10 tornadoes worldwide that inflicted a greater toll than the potential 400-plus deaths abroad the Oriental Star. As we’ll see below, the event also brings to mind a similar U.S. tragedy almost 40 years ago.

Figure 1. Rescuers search for survivors from the capsized ship Dongfangzhixing (Eastern Star) in the Yangtze River on June 2, 2015, in Jingzhou, China. Image credit: ChinaFotoPress/Getty Images.

What caused the high winds?
Press coverage has led to some understandable confusion over exactly what caused the disaster. China’s Xinhua news agency reported that the China Meteorological Agency (CMA) detected winds “stronger than 12 scale,” apparently a reference to the Beaufort scale, where 12 corresponds to winds exceeding hurricane force (74 mph). The Guardian cites local media as reporting winds of 80 mph at the time of the accident. Several news reports called the event a cyclone, while others dubbed it a tornado. Given that tornadoes have cyclonically oriented winds, they are sometimes referred to as cyclones in news reports outside the United States. Moreover, according to the New York Times, “In Chinese, the term for tornado, longjuanfeng, is used more loosely than Americans use its English equivalent.”

Figure 2. An infrared satellite image taken at around midnight local time on Monday night, June 1, several hours after the Eastern Star ship was hit by high winds. Image credit: An infrared loop from Japan’s new Himawari-8 satellite illustrates the same storm complex, with an blue “X” placed at the approximate location of the capsizing. Image credit: Japan Meteorological Agency, courtesy Dan Lindsey, Cooperative Institute for Research in the Atmosphere.

Satellite images from the region around the disaster show a large cluster of strong thunderstorms developing on Monday night local time (see Figure 2). Eastern Asia has some of the same thunderstorm-favorable features as the U.S. Great Plains, including mountains and dry air to the west and access to very warm, humid air toward the south and east. However, little has been published in the global science literature on the frequency of tornadoes across China. “Thunderstorms have certainly been plentiful across eastern and southern China over the past few days," said Jon Erdman in a article. "It's certainly possible one of those thunderstorms may have spawned a very unfortunately-timed tornado. . . .Also, strong straight-line, non-tornadic winds—common in clusters of thunderstorms like those seen in eastern China late Monday—may have played a role in the capsizing."

Harold Brooks (NOAA National Severe Storms Laboratory), an expert on international tornado climatology, inspected upper-air soundings collected across the central Yangtze region on Monday evening. Brooks told me the soundings were supportive of tornadic supercells, with ample instability (CAPE values of 1000 to 3000 J/kg) and adequate storm-relative helicity (a measure of potential updraft rotation). However, such conditions can also lead to high-precipitation storms that produce strong downburst winds but no tornado. “Given the environment, I wouldn't be surprised if it was a tornado or, at least, a strong rear-flank downdraft associated with a supercell,” said Brooks.

Monday’s storms developed along a seasonal feature called the Mei-yu front, a band of convergent winds associated with the northward push of the Asian monsoon in China and Japan. Each spring, the cold, parched winter climate of China transitions to a muggy summer regime that includes frequent rounds of torrential rain. Beijing’s average precipitation in July (7.3”) is far greater than its average in January (0.1”). The Asian monsoon is driven by southwesterly upper winds toward the northeast, so it reaches a higher latitude sooner than the Indian monsoon. This explains why heavy rains can strike central China (latitude 30°N) while parts of India as far south as 10°N have yet to see the monsoon. The Mei-yu front can stall out for weeks during May and June in the general vicinity of the Yangtze, leading to days of heavy thunderstorms along and near it. BBC reported that the Mei-yu rains this season have been the heaviest in 40 years across parts of south China.

Figure 3. A bridge damaged by flood water in Leishan county of southwest China’s Guizhou province on May 27, 2015. Parts of China have been hit by the heaviest spring rains in 40 years. Image credit: AFP/Getty Images.

The Whippoorwill disaster of 1978
Though far less deadly than its present-day counterpart in China, the capsizing of a pleasure boat called the Whippoorwill led to one of the ten worst tornado tolls in the history of Kansas. On June 17, 1978, the Whippoorwill carried 58 passengers on an evening cruise on the 4,000-acre Pomona Lake, about 30 miles south of Topeka. A small tornado, only about 150 yards wide but with multiple vortices, developed near the lake around 7:00 pm, according to a summary from the National Weather Service office in Topeka. Damage was minimal, but the suddenness of the tornado’s development and its unfortunate path led to the capsizing of the showboat. One victim recalled: “One minute we were serving salads, the next I was under water.” There were 16 fatalities. “Nationwide media coverage was focused on Kansas and this tornado for many days after the tragic event,” notes the NWS/Topeka. “People who boarded the Whippoorwill for an evening of fun and entertainment, likely never imagined what a historical catastrophe they were in for.” As part of the 50th anniversary of the creation of Pomona Lake, a memorial service was held last June 17 for the victims of the Whippoorwill disaster.

My thanks go to Harold Brooks (NOAA/NSSL), Roger Edwards (NOAA Storm Prediction Center), and WU weather historian Christopher Burt for background used in this article.

Bob Henson


The Amazing Rains of May: Photos and Stats

By: Bob Henson , 2:35 PM GMT on June 02, 2015

Now that May has mercifully drawn to a close, and the south-central states are drying out and cleaning up, we can take full measure of what an incredibly, destructively soggy month it was, especially for Texas and Oklahoma. Both states obliterated their rainfall records for any calendar month going back to 1895. While the rains quickly doused a multiyear drought (see Figure 3 below), the flooding killed at least 31 people, with 6 others missing as of Monday night, and inflicted at least $1 billion in damage, according to estimates from the insurance broker Aon Benfield. Below are a few memorable images from the past month—but first, some numbers:

Figure 1. Top-ten wettest months in the statewide averages for Oklahoma and Texas. The May 2015 values are preliminary. Data courtesy Gary McManus and John Nielsen-Gammon, the state climatologists for OK and TX respectively, from a database maintained by NOAA’s National Centers for Environmental Information (formerly the National Climatic Data Center).

As Figure 1 shows, the totals for both TX and OK in May exceeded the previous records by more than 30%, truly a phenomenal outcome. In fact, the gaps between the #1 and #2 outcomes are far larger than the gaps between #2 and #10! Texas state climatologist John Nielsen-Gammon (Texas A&M University) came up with a back-of-the-envelope estimate for how often you would expect such an extremely wet month in his state: about every 2000 years, assuming the climate of the past century were to persist. For more on the science behind recurrence intervals such as this and how they’re produced, see our post from last Saturday. Interestingly, no other single month appears on the top-ten wettest lists for both Texas and Oklahoma—another sign of how unusually widespread and persistent this event was.

The rains of May made weather history on a local scale as well. WU weather historian Christopher Burt assembled the preliminary list below of some cities that notched their all-time wettest months in May, including their periods of record (POR).

Ft. Smith: 19.85” (previous record 15.02”, June 1945; POR began 1882)

Colorado Springs: 8.13” (previous record 8.10”, May 1935; POR began 1894, with some data back to 1871)
La Junta: 7.38” (previous record 6.27”, Aug. 1916; POR began 1910)
Eads: 9.25” (previous record 8.60”, July 2014; POR began 1907)
Ft. Morgan 10.46” * (previous record 9.98”, Apr. 1900; POR began 1896)
(*Ft. Morgan data are from a CoCoRaHS station and not official)

Oklahoma City: 19.48” (previous record 14.66”, June 1989; POR began 1891)
Lawton: 20.47” (previous record 16.67” ,June 2007; POR began 1912)

Wichita Falls, TX: 17.00” (previous record 13.22”, May 1982; POR began 1897)
Childress, TX: 13.21” (previous record 12.05”, May 1941; POR began 1897)

Burt adds: “The wettest location in the Oklahoma Mesonet was Lane, with an amazing 28.17”. If official, this would smash the previous OK state monthly precipitation record of 23.95”, set at Miami in May 1943.”

Bob Henson

Figure 2. Rainfall in May 2015 was far above all previous Mays in the Oklahoma City climatological record, as shown in this trace of cumulative totals achieved day by day. Image credit: Patrick Marsh, @pmarshwx.

Figure 3. The definition of Weather Whiplash: portions of Texas and Oklahoma went from the most extreme category of drought--"Exceptional"--to no drought whatsoever in just four weeks. A five-class improvement in drought in such a short period of time is bound to lead to serious flooding.

Figure 4. Sunlight filtered through clouds and rain casts a copper glow on flooded field near Lubbock, TX. The city saw a spectacular, drought-quenching series of storms in late May, although the month’s 12.12” of rain fell short of May 1941 (12.69”) and September 1936 (13.93”). Image credit: Jason Davis.

Figure 5. In Oklahoma City on May 23, a truck powers its way through high water--and serves a good example of what to avoid when behind the wheel during heavy rain. As little as two feet of water can sweep most vehicles off the road, and it only takes a few inches of water to obscure a road that might be washed out. (Jim Beckel/The Oklahoman via AP.

Figure 6. Canoes replaced motor vehicles on a road near Bear Creek Park in west Houston on May 30. Interpolation from rain gauges suggests that upwards of 13” of rain fell in 24 hours over one part of southwest Houston. Widespread flooding inundated large parts of the urban area. Image credit: AP Photo/David J. Phillip.

Figure 7. In northeastern Oklahoma, water poured through the Robert S. Kerr Lock and Dam along the Grand River on May 30 at the rate of 349,000 cubic feet per second, or about four times the average flow rate over Niagara Falls. Image credit: Tulsa District, U.S. Army Corps of Engineers.

Figure 8. Mike Graf stands on the foundation of his home near Wimberley, TX, on Stone Canyon Street after it was completely swept away by the Blanco River in the flood on Saturday night, May 23. "It's only things," he said. The flooding killed at least 8 people along the Blanco River, with several others still missing, and destroyed dozens of homes in and near Wimberley. Image credit: Jay Janner/Austin American-Statesman via AP.

Figure 9. This campground at Kaw Lake, in north-central Oklahoma near Ponca City, wasn’t getting much use on June 1. Image credit: wunderphotographer CReese.

Figure 10. The calm after the storm: a photo taken on Memorial Day, May 25, after the flooding had peaked at Bastrop, TX. Image credit: wunderphotographer Kiowa63.

Flood Extreme Weather

The 2015 Atlantic Hurricane Begins; New CSU, TSR Forecasts Call For a Quiet Season

By: Jeff Masters , 2:34 PM GMT on June 01, 2015

The 2015 Atlantic hurricane season is officially underway. We've already had one early season storm, Tropical Storm Ana; will we have an early June Tropical Storm Bill? There are indications that the second tropical depression of the year has a chance to form late this week in the waters near South Florida or the Bahama Islands on Friday or Saturday. We have warmer than average SSTs in these waters, and the Madden-Julian Oscillation (MJO) is expected to be active in the Western Hemisphere late this week, and both of these factors argue for higher than usual odds of an early June tropical depression forming in the Atlantic. Over the past few days, the GFS model has been consistently advertising the possibility that an area of low pressure capable of developing into a tropical depression will form in this region, although the European model (so far) has not gone along with this idea. If we do get something developing, it would potentially be a heavy rain threat for South Florida and the Northern Bahamas over the weekend, but then move northeastwards out to sea without troubling any more land areas.

Figure 1. The strongest Atlantic hurricane of 2014, Hurricane Gonzalo, as seen from the International Space Station on October 16, 2014. At the time, Gonzalo was at peak strength, with 145 mph winds, and was the first Atlantic hurricane to reach sustained winds of at least 145 mph since Hurricane Igor of 2010. Gonzalo hit Bermuda just a week after Hurricane Fay hit the island, and Gonzalo's remnants went on to batter the United Kingdom on October 21 with wind gusts exceeding 100 mph, killing three people there. Image credit: Alexander Gerst.

Summary of the 2015 Atlantic hurricane season forecasts
The major hurricane forecasting groups are not impressed with this season's potential to be an active one, and are universally calling for 2015 to be a below average to way below-average year for the Atlantic. The highest forecast numbers were from Weather Underground Community Hurricane Forecast, which called for 11 named storms, 5 hurricanes, and 2 major hurricanes. The lowest numbers were from North Carolina State University: 5 named storms, 2 hurricanes, and 1 intense hurricane. The long-term averages for the past 65 years are 11 named storms, 6 hurricanes, 3 intense hurricanes. Here are the forecasts:

NOAA: 8.5 named storms, 4.5 hurricanes, 1 major hurricane, ACE index 62.5% of normal.
Colorado State University (CSU): 8 named storms, 3 hurricanes, 1 major hurricane, ACE index 44% of normal.
Tropical Storm Risk, Inc. (TSR): 10 named storms, 4 hurricanes, 1 intense hurricane, ACE index 36% of normal.
UKMET office: 8 named storms, 5 hurricanes, ACE index 74% of normal (June - November.)
FSU Center for Ocean-Atmospheric Prediction Studies (COAPS):
Weather Underground Community Hurricane Forecast: 11 named storms, 5 hurricanes, 2 major hurricanes
WSI: 9 named storms, 5 hurricanes, 1 major hurricane
Penn State: 8 named storms.
North Carolina State University: 5 named storms, 2 hurricanes, 1 intense hurricane.
Coastal Carolina University: 8 named storms, 4 hurricanes, 2 intense hurricanes.
The Cuban Meteorological Service, INSMET: 9 named storms, 3 hurricanes.

The main reason for the quiet forecasts is the likely intensification of the current moderate strength El Niño. Every 3 - 7 years, variations in tropical winds and pressure shift warm ocean waters eastwards from the Western Pacific to the South American coast, causing an El Niño event. The unusually warm water tends to drive an atmospheric circulation that brings strong upper-level winds to the tropical Atlantic, creating high levels of wind shear that tend to tear hurricanes apart. Another factor leading to lower forecast numbers than in previous years is the fact that sea surface temperatures in the tropical Atlantic are near average to below average this year--quite a bit cooler than we've seen during the typical year during our active hurricane period that began in 1995.

Figure 2. Departure of sea surface temperature (SST) from average for May 30, 2015. SSTs were near average to slightly below over the Atlantic Main Development Region (MDR) for hurricanes, from the coast of Africa to Central America between 10°N and 20°N, including the Caribbean. As of June 1, 2015, SSTs over the region typically used to define El Niño events, 5°N - 5°S to 120°W - 170°W (the Niño 3.4 region) were in the moderate for El Niño conditions, +1.3°C from average, according to the latest weekly NOAA El Niño update. Image credit: NOAA/NESDIS.

Colorado State predicts a below-average hurricane season: 8 named storms
A new Atlantic hurricane season forecast issued June 1 by Dr. Phil Klotzbach and Dr. Bill Gray of Colorado State University (CSU) again calls for a below-average season with 8 named storms, 3 hurricanes, 1 intense hurricane, and an Accumulated Cyclone Energy (ACE) of 40, which is about 44% of average. The forecast calls for a below-average chance of a major hurricane hitting the U.S., both along the East Coast (15% chance, 31% chance is average) and the Gulf Coast (15% chance, 30% chance is average). The risk of a major hurricane in the Caribbean is also below average, at 22% (42% is average.) The June 1 numbers are nearly unchanged from their April 9 forecast, with the exception of an additional named storm (due to the formation of Tropical Storm Ana in May.)

CSU's Analogue years: 1997, 1987, 1982, 1972, 1965, and 1957
The CSU team picked six previous years when atmospheric and oceanic conditions were similar to what they expect for this year: at least moderate El Niño conditions, and generally cool sea surface temperatures in the tropical Atlantic. Those years were 1997 (which featured 8 named storms, 3 hurricanes, and 1 intense hurricane); 1987 (7 named storms, 3 hurricanes, and 1 intense hurricane); 1982 (6 named storms, 2 hurricanes, and 1 intense hurricane); 1972 (7 named storms, 3 hurricanes, and 0 intense hurricanes); 1965, featuring Hurricane Betsy, which hit New Orleans as a Category 3 storm; and 1957, which featured the deadliest June hurricane on record, Hurricane Audrey, which killed 416 people in Texas and Louisiana. The average activity for these years was 7 named storms, 3 hurricanes, and 1 major hurricane.

TSR predicts a below-average hurricane season: 10 named storms
The May 27 forecast for the 2015 Atlantic hurricane season made by British private forecasting firm Tropical Storm Risk, Inc. (TSR) calls for a below-average season with 10 named storms, 4 hurricanes, 1 intense hurricane, and a remarkably low Accumulated Cyclone Energy (ACE) of 37. The long-term averages for the past 65 years are 11 named storms, 6 hurricanes, 3 intense hurricanes, and an ACE of 102. TSR rates their skill level as modest for these late May forecasts: 6 - 24% higher than a "no-skill" forecast made using climatology. They project that 2 named storms will hit the U.S., with 1 of these being a hurricane. The averages from the 1950-2014 climatology are 3 named storms and 1 hurricane hitting the United States. TSR rates their skill at making these May forecasts for U.S. landfalls just 4% - 8% higher than a "no-skill" forecast made using climatology. In the Lesser Antilles Islands of the Caribbean, TSR projects one named storm and no hurricanes in 2014. Climatology is 1.1 named storms and less than 0.5 hurricanes.

TSR's two predictors for their statistical model are the forecast July - September trade wind speeds over the Caribbean and tropical North Atlantic, and the forecast August - September 2015 sea surface temperatures (SSTs) in the tropical North Atlantic Main Development Region (MDR) for hurricanes. Their model is calling for SSTs 0.33°C below average and trade winds 1.36 m/s stronger than average during these periods; both of these factors should act to decrease hurricane and tropical storm activity. The July-September 2015 trade wind prediction is based on an expectation of weak El Niño conditions in August-September 2015. TSR will issue an updated forecast on July 6, 2015.

Even a quiet hurricane season can be devastating
Quiet hurricane seasons with below-average activity can still produce major hurricanes that cause massive devastation. The five seasons that CSU lists as analogue years for 2015 produced four hurricanes that had their names retired, including one that killed 8,000 people in Cuba (Flora of 1963) and one that killed over 400 people in Texas and Louisiana (Audrey of 1957.) Even if this is an El Niño year, that doesn't mean it will be a quiet season. Recall the El Niño year of 2004, when four major hurricanes pounded the U.S.--Ivan, Charlie, Jeanne, and Frances. Those of you in Hurricane Alley should prepare for the 2015 season the same way you would for a predicted hyperactive season, and be ready for the Storm of the Century to hit your location.

Good luck to everyone in Hurricane Alley this hurricane season, and I look forwards to tracking all the activity this year with you!

Jeff Masters

Andres Becomes the Farthest West Major Hurricane on Record for May in the NE Pacific

By: Jeff Masters , 2:57 AM GMT on June 01, 2015

Hurricane Andres became only the fifth major May hurricane on record in the Northeast Pacific on Sunday, when it intensified into a 125 mph Category 3 storm in the waters about 800 miles southwest of the tip of Mexico's Baja Peninsula. Its unexpected intensification continued Sunday evening, with Andres reaching Category 4 strength with 140 mph winds at 11 pm EDT. According to the database of Eastern Pacific storms maintained by NOAA's Office for Coastal Management, Andres' emergence as a major hurricane at longitude 118.8°W marks the farthest west a major hurricane has been in the Northeast Pacific in May in the 45 years since accurate satellite records began in 1970, and comes well before the usual July 19 formation date of the first major hurricane of the Northeast Pacific hurricane season. This unusually early and far westerly intensification was made possible, in part, by sea surface temperatures (SSTs) that are very warm, at least 2°F (1.1°C) above average--thanks in large part to the intensifying moderate-strength El Niño event underway in the Eastern Pacific. The other May major hurricanes were Adolph (2001), Alma (2002), Bud (2012), and Amanda (2014). The strongest was Hurricane Amanda, which peaked as a top-end Category 4 hurricane with 155 mph winds on May 25, 2014. The earliest Category 5 storm on record in the Eastern Pacific was Hurricane Ava of 1973, which peaked at 160 mph winds on June 6, 1973. Both years (2014 and 1973) had ocean temperatures that were unusually warm along the path of these intense hurricanes: at least 0.4°C above average. Andres will stay well out to sea and not affect any land areas.

Figure 1. MODIS image of Hurricane Andres taken at approximately 2 pm EDT May 31, 2015. At the time, Andres was intensifying into a Category 3 storm with 125 mph winds. Image credit: NASA Worldview.

Figure 2. Tracks of all May tropical storms and hurricanes in the Eastern Pacific Ocean according to the database maintained by NOAA's Office for Coastal Management. The 2015 version of Hurricane Andres became a major hurricane on Sunday afternoon at 5 pm EDT May 31 (large orange X) farther west than any previous May major hurricane has existed in the Northeast Pacific (accurate records of Eastern Pacific tropical cyclones began in 1970.) The previous record was 115.4°W by Hurricane Alma of 2002.

Tropical Depression 2-E forms in the Northeast Pacific
Hurricane Andres now has a companion--Tropical Depression 2-E, which formed Sunday afternoon about 380 miles SSW of Zihuatanejo, Mexico. TD 2-E is suffering high wind shear due to the upper-level outflow from Hurricane Andres, but will likely see lower wind shear by Tuesday and become Tropical Storm Blanca as Andres moves off to the west. Intensification into a major hurricane is predicted by NHC by the end of the week. TD 2-E will not be a threat to any land areas this week, but it is too early to say if it will miss the coast of Mexico next week or not. The usual appearance of the second named storm of the Northeast Pacific hurricane season comes on June 25.

NOAA predicts an above-average Eastern Pacific hurricane season: 18.5 named storms
Andres and TD 2-E are the first salvos in what is likely to be a very busy Northeast Pacific hurricane season. NOAA's pre-season prediction for the Eastern Pacific hurricane season, issued on May 27, calls for 15 - 22 named storms, 7 - 12 hurricanes, 5 - 8 major hurricanes, and an ACE index 110% - 190% of the median. The mid-point of these ranges gives us a forecast for 18.5 named storms, 9.5 hurricanes, and 6.5 major hurricanes, with an ACE index 150% of average. The 1981 - 2010 averages for the Eastern Pacific hurricane season are 15 named storms, 8 hurricanes, and 4 major hurricanes.

I'll have a new post late morning on June 1--the beginning of the Atlantic hurricane season.

Jeff Masters


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

Category 6™


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