Category 6™

Paris Climate Talks Begin; Five Reasons Why They Are So Important

By: Bob Henson , 3:51 PM GMT on November 30, 2015

A momentous two weeks of United Nations meetings that will shape the future of Earth’s climate have begun. The 21st annual UN Conference on Climate Change (also known as the Conference of Parties, or COP21) will unfold at Le Bourget, France, about six miles northeast of downtown Paris. COP21 is bringing together some 40,000 diplomats, scientists, journalists, and observers, as well as 151 heads of state--the largest such gathering of world leaders in history. A virtual tour of the COP21 site gives a quick 3-D sense of the massive size of this undertaking. The attacks in Paris on November 13 have not caused any major disruption to the formal proceedings, although off-site protests in the Paris area have been banned. Activists around the world took part over the weekend in a Global Climate March that drew hundreds of thousands to the streets. (Climate activists undeterred by the protest ban in central Paris were teargassed, and more than 200 were detained by police.)

Figure 1. Bogata, Colombia, was one of many dozens of cities taking part in the Global Climate March on November 29, 2015. Image credit: Guillermo Legaria/AFP/Getty Images.

Figure 2. Women dressed as angels holds signs at the Place de la Repubique in Paris where hundreds of pairs of shoes were placed on November 29, 2015, on the eve of the official opening of the UN COP21 conference. The shoes were placed as part of a symbolic and peaceful rally called by the nongovernmental organization Avaaz. Image credit: Miguel Medina/AFP/Getty Images.

COP meetings occur each year, but this one has drawn the most attention since COP15 (2009) in Copenhagen. That meeting fell far short of hopes for drafting a global agreement for greenhouse-gas emission cuts that would succeed the 1997 Kyoto Protocol. This year’s meeting represents the best chance at a workable global agreement since Copenhagen--and perhaps our last chance for a long time to come. What makes COP21 so critical?

1. We’ve lost years of precious time.
Scientists have known for decades that our ever-increasing output of greenhouse gases would lead to global warming, but the world has dragged its collective feet in taking global steps to reduce emissions. Some of this is due to active cultivation of doubt by political and industrial leaders in the U.S., which was the world’s leading greenhouse emitter until the last decade. (Exxon’s downplaying of climate risks, on the heels of its own extensive research showing the reality of climate change, is a dramatic example that’s come to light this year through major investigative work.) Even if everyone in the world acknowledged the risks at hand, it would remain a Herculean task to modify the world’s reliance on fossil fuels. Global leaders--including U.S. President George H.W. Bush--signed on to the 1992 UN Framework Convention on Climate Change, which mandated the avoidance of “dangerous anthropogenic interference with the climate system”. The Kyoto Protocol was first attempt at putting those words into action, but the agreement had several major flaws--including the fact that the United States decided not to ratify Kyoto and, as a developing nation, China wasn’t initially required to cut its emissions. In effect, both the U.S. and China used the other country’s non-participation as carte blanche to carry out business as usual. This meant that nearly half of the world’s greenhouse emissions went unregulated by Kyoto. Unsurprisingly, the world’s greenhouse output has continued to soar. In 1997, global CO2 emissions added up to 24.4 billion metric tons, according to the Netherlands Environmental Assessment Agency. In 2014, the total was 35.7 billion metric tons--a sobering increase of 46%. Much of this CO2 will be acting to warm our climate centuries and even millennia from now, but we’ve already seen dramatic changes since 1997, from massive polar ice loss to unrelenting sea level rise.

Figure 3. Two ways to look at carbon dioxide emissions in 2013 around the world: (top) the 18 nations with the greatest total emissions, and (bottom) the emissions per capita from those 18 nations. Larger dots indicate greater emissions. China has quickly outpaced all other nations in total CO2 emissions, due to its huge population and fast-growing economy, but the typical American is still responsible for more CO2 output than the typical person in China. Image credit: Netherlands Environmental Assessment Agency.

2. Individuals can’t do it all.
Each of us can make big cuts in our carbon footprint through simple changes in how we get around, how efficiently we heat and cool our homes, and what we eat. These actions not only reduce emissions but also help motivate us to get friends and neighbors interested in addressing climate change. Plus, as consumers demand energy-efficient alternatives, it spurs the marketplace to provide them. All of this is good news for climate, but there must be a worldwide agreement with at least some teeth in order to ensure truly global emission cuts. Otherwise, energy spendthrifts will take advantage of supply and demand to burn the fossil fuel that others manage to save through efficiency. A globally agreed price on carbon could leverage the power of the marketplace to accelerate emission reduction. Such a target is not part of the Paris agenda; however, if the world’s nations do come to agreement in other ways in Paris, it could help pave the way for eventual consideration of a global price on carbon.

3. For the first time, most nations are ready to commit to long-term emission cuts.
The Kyoto Protocol was hobbled largely by its division of the world into developed and developing nations, with the latter spared from mandated emissions cuts for the time being. The idea was that developing nations should have the same chance to build their economies that developed nations had already gotten. But the massive growth of international trade complicated the picture, because it allowed nations like China to grow rapidly while manufacturing things for developed countries--thus allowing those countries to “offshore” some of their emissions. Recognizing this flaw, organizers of the Paris summit have created a system through which each nation comes up with its own emissions goals. Going into the Paris meeting, a total of 176 nations representing more than 95% of carbon dioxide emissions have submitted what are known as Intended Nationally Determined Contributions (INDCs). Together, these INDCs will not be enough to keep the world’s climate from edging beyond the 2°C warming above pre-industrial levels that is typically assumed to be the threshold of "dangerous" climate change. At best, it appears they would keep warming closer to 2.7°C. So it’ll be vital that the Paris agreement include at least some mechanisms for strengthening the plans over time.

4. A successful outcome in Paris could jump-start other action.
We already have the ability to deploy current forms of renewable energy (such as solar and wind power) at scales far larger than now exist. With a concerted effort, new technology could catalyze the process. This is the idea behind Monday’s announcement of the world’s largest-ever partnership for clean-energy research and development, involving a group of nations teaming with Bill Gates and other global billionaires.

5. It could be many years before the stars align this way again.
Given its outsized role in world affairs, the participation of the United States in any global climate deal is absolutely crucial. Yet the U.S. remains a world capital of climate-change misunderstanding. As shown in Figure 2, a poll this year by Yale University and George Mason University found that only about half of Americans believe that, assuming global warming is happening, humans are responsible for it (and only about two-thirds of Americans think that climate change is occuring at all). These numbers have changed little since 2009, though a different series of polls conducted since 2012 by the University of Texas suggests there may in fact be a recent shift toward greater climate-change acceptance.

Figure 4. Results of the polling of randomly selected Americans conducted from November 2008 (far left) to March 2015 (far right) by Yale University/George Mason University. The question: “Assuming global warming is happening, do you think it is caused mostly by human activities, or mostly by natural changes in the environment?” Image credit: Yale Project on Climate Change Communication.

The Climate Action Plan put forth in 2013 by President Barack Obama includes many concrete steps toward emission reduction, most importantly through the restrictions on U.S. coal plants. Yet the plan has already faced stiff resistance in the U.S. Congress. Depending on the outcome of the 2016 elections, the U.S. commitment to climate action is far from set in stone, which makes any agreement reached in Paris all the more important.

How to follow COP21
WIth so many journalists on the scene, and so much happening, we can expect an avalanche of coverage over the next few days. The most newsworthy periods should be the first couple of days, as world leaders assemble, and late next week, as any agreement(s) are finalized. Here are some good sources for frequently updated material:

Mashable (see also Mashable’s excellent guide to the climate talks)
Seth Borenstein, Associated Press
The Guardian
Climate Central
The Daily Climate
World Resources Institute

WU climate blogger Ricky Rood has posted a
series of blogs in the run-up to Paris, including a guide to the evolution of the COP meetings. Ricky’s words are worth keeping in mind as the events in Paris unfold: “My understanding is that the present INDC contributions produce a few percent real reduction of emissions by 2030. Though this will not avoid climate change, we have known this to be the case for many years. Hence, no surprise, and I worry that this will be construed as hopelessness or failure. If there is a real reduction by 2030, and we have avoided that descent to the Dark Ages, this will be an amazing achievement. “

Two students from the University of Michigan received a scholarship from Weather Underground to attend the Paris meetings: Lizz Ultee and Matt Irish. Lizz Ultee, a doctoral candidate, is studying how glaciers contribute to global mean sea level rise. She values a holistic, justice-centered approach to her work and looks forward to learning how natural science research is translated into worldwide policy in the UNFCCC process. Matt is finishing up an undergraduate degree studying climate science and how our understanding of climate change is informing the transition toward cleaner energy systems.

Figure 5. Lizz Ultee (left) and Matt Irish (right).

Lizz sent us these initial thoughts from Paris on Monday:

"I’ve been deeply impressed by the organization of the COP today. We were expecting long lines and the assorted delays usually associated with convening tens of thousands of people in one (extremely secure) place, but thus far we have passed quite smoothly almost everywhere. Dozens of security lanes minimized the delays of x-ray and metal detector screening at the entrance, and the huge site seems to spread people out. There are 40,000 people here, but I’ve only been encountering a few hundred--rather than a few thousand--at a time. It all feels very well planned and managed. The morning started off with the opening ceremony and leaders’ statements. Many statements were in French or a mixture of French and English, with live translation provided via the headphones I’ve always seen on videos of UN proceedings. I was disproportionately excited to get to use live-translation headphones for the first time in my life. Observers were not permitted in the main hall and had to watch via CCTV in an adjoining room, but I suppose security has to be at its tightest for the largest-ever gathering of world heads of state. Having 150 heads of state together in one room would be powerful under any circumstances--literally, it is an unprecedented concentration of power--but it makes an especially stirring kick-off to the hard work of COP21.”

Lizz and Matt will be posting updates to the website Climate Blue and tweeting from @climateblue as COP21 progresses.

Bob Henson

Climate Change Politics Climate Change

High Wind Shear Rips Apart Tropical Storm Sandra

By: Jeff Masters , 3:24 PM GMT on November 28, 2015

Something to give thanks for this holiday weekend: Tropical Storm Sandra was shredded apart by 50 knots of wind shear early Saturday morning before the storm could make landfall on the Pacific coast of Mexico, ending the reign of this most unusual late-season storm. Earlier in the week, record-warm ocean waters helped Sandra set the record for the latest major hurricane ever observed in the Western Hemisphere, as the storm maintained at least Category 3 strength from 21 UTC November 25 through 03 UTC November 27 (previous record: an unnamed Atlantic hurricane in 1934 that held on to Category 3 status until 00 UTC November 24.) When Sandra peaked as a Category 4 storm with 145 mph winds on November 26, it became the latest Category 4 storm ever observed in either the Eastern Pacific (previous record: Hurricane Kenneth on November 22, 2011) or the Atlantic (previous record: "Wrong Way" Lenny on November 18, 1999.) Prior to Sandra, the strongest East Pacific hurricane so late in the year was 1983’s Winnie, which topped out on December 6 at 90 mph winds. Sandra was also the first major hurricane in the Western Hemisphere that has ever been observed on Thanksgiving Day. Sandra was the record-shattering 25th Category 4 or stronger tropical cyclone in the Northern Hemisphere in 2015. According to wunderblogger Dr. Phil Klotzbach's Twitter feed, the previous record was eighteen such storms in 1997 and 2004.

Figure 1. MODIS satellite image of Hurricane Sandra taken at approximately 2 pm EST November 27, 2015. At the time, Sandra was a Category 1 storm with 80 mph winds, and was rapidly being shredded apart by high wind shear. Image credit: NASA.

Figure 2. Projected 3-day precipitation totals (rain and melted snow/sleet) for the period from 7 am EST Saturday, November 28, through Tuesday, December 1.

Moisture associated with Sandra fuels heavy rain event over Texas
Moisture streaming ahead of Sandra from the tropical Eastern Pacific into the Southern U.S. contributed to a heavy rainfall event over Texas and Oklahoma on Thursday and Friday, and this tropical moisture will continue to fuel heavy rains across portions of Arkansas, Mississippi, and Tennessee during the remainder of the holiday weekend. The rain of 3.45" that fell Friday on Dallas-Fort Worth gave them their wettest November calendar day on record, their wettest November on record (7.99" so far, previous record 7.94" in 1918), their wettest fall on record (now up to 19.95"), and their wettest year on record (now 56.91", previous record 53.54" set in 1991.) Thanks go to TWC's Michael Palmer for these stats.

Have a great rest of your Thanksgiving weekend, everyone!

Jeff Masters


Hurricane Sandra Heads for Mexican Coast; Icing, Flooding Hit Southern Plains

By: Bob Henson and Jeff Masters , 4:36 PM GMT on November 27, 2015

After becoming the latest major hurricane on record in the Western Hemisphere, a weakening Hurricane Sandra remained on track Friday for a history-making landfall early Saturday on the coast of Mexico’s Sinaloa state. A Tropical Storm Warning was in effect for Las Islas Marias and for Mexico’s Pacific coast from Altata to San Blas, including the Mazatlan area. Sandra will be a fast-decaying storm by that point, but even in that condition, it should be a record-setter: no tropical cyclone on record has made landfall so late in the year on either the Atlantic or Pacific coast of Mexico. The current record-holder is Tara (Nov. 12, 1961).

Figure 1. Enhanced infrared satellite image of Hurricane Sandra as of 10:37 am EST Friday, November 27, 2015.

Sandra peaked at Category 4 strength early on Thanksgiving Day (November 26), with top sustained winds briefly hitting an eye-popping 145 mph. The previous record-latest major hurricane in the Western Hemisphere was an unnamed Atlantic hurricane in 1934 that held on to Category 3 status until 00 UTC November 24. Sandra is also now the latest Category 4 storm ever observed in either the Eastern Pacific (previous record: Hurricane Kenneth on November 22, 2011) or the Atlantic (previous record: "Wrong Way" Lenny on November 18, 1999.) Sandra’s peak winds had decreased to 85 knots (100 mph) by the time of the 11 AM EST Friday advisory from the National Hurricane Center. Wind shear has picked up dramatically over Sandra’s track, giving the storm a comma shape more akin to a hybrid or subtropical cyclone (see Figure 1), but Sandra has managed to maintain a small, intense convective core while picking up forward speed. Well before landfall, the strong shear is expected to push Sandra’s mid-level circulation ahead of its low-level center, hastening the storm’s demise.

Figure 2. Multisensor-observed precipitation for the 24-hour period ending at 6:00 am CST Friday, November 27, 2015. Image credit: NWS Advanced Hydrologic Prediction Service.

Record Thanksgiving Day rains--and more to come
A sprawling upper-level low in the southwest U.S. teamed up with unusually rich Gulf moisture (record amounts for the time of year in some locations) to make for a very soggy Thanksgiving over much of the central U.S. Factoring in the various year-to-year dates of Thanksgiving Day, Thursday qualified as the wettest Thanksgiving Day on record by an ample margin for several cities with century-plus periods of record, including:

Wichita, KS (1.66”, old record 0.81” in 1977)
Milwaukee, WI (1.55”, old record 0.98” in 1968)
Madison, WI (1.19”, old record 1.06” in 1879)
Rockford, IL (1.51”, old record 0.81” in 1918)
Kansas City, MO (1.61”, old record 1.19” in 1896)
[Thanks to Michael Butler, The Weather Channel, for these statistics]

Some of the heaviest rains struck the Dallas-Fort Worth area, where at least two motorists were killed in overnight flooding. The year 2015 is now officially the wettest on record for the nation’s fourth largest metropolitan area. From Thursday afternoon through 8:53 AM CST Friday, the Dallas/Fort Worth Metropolitan Airport received 4.51” of rain, pushing their year-to-date total to 55.26” with five weeks still left in the year. The previous annual record was 53.54,” set in 1991. Weather records in the DFW area began at downtown Fort Worth in 1898. A few localized areas in southeast Oklahoma and east Texas have racked up more than 70” of rain this year, with more than 80” in places between Houston and Beaumont. Baytown picked up 90.21” from January through October, notching more than 5” in every month except February.

Moisture and energy from Hurricane Sandra will be flowing over Texas this weekend, adding to the multiday deluge now under way. Various flood and flash flood watches and warnings are in effect from north Texas to southwest Illinois, with Arkansas in line for especially heavy rain falling over rugged, flood-prone terrain. Further northwest, ice storm warnings remain in effect from far eastern New Mexico to parts of south central Kansas, with ice accumulations of more than half an inch possible in some areas. Some roadway icing is expected, but with air temperatures staying close to freezing in many areas, the biggest hazard of this prolonged event may be from ice-encrusted tree limbs and power lines.

Whether or not you’re traveling this weekend, take care and stay safe!

Bob Henson and Jeff Masters

Hurricane Flood Winter Weather

An Unprecedented Thanksgiving Visitor: a Category 4 Hurricane

By: Jeff Masters and Bob Henson , 4:18 PM GMT on November 26, 2015

Remarkable Hurricane Sandra exploded into a Category 4 storm with 145 mph winds overnight, making it the latest major hurricane ever observed in the Western Hemisphere (November 26.) The previous record was held by an unnamed Atlantic hurricane in 1934 that held on to Category 3 status until 00 UTC November 24. Sandra is also now the latest Category 4 storm ever observed in either the Eastern Pacific (previous record: Hurricane Kenneth on November 22, 2011) or the Atlantic (previous record: "Wrong Way" Lenny on November 18, 1999.) Prior to Sandra, the strongest East Pacific hurricane so late in the year was 1983’s Winnie, which topped out on December 6 at 90 mph winds. Sandra is the first major hurricane in the Western Hemisphere that has ever been observed on Thanksgiving Day. According to WU contributor Phil Klotzbach (Colorado State University), Sandra is on track to become the latest landfalling tropical cyclone on record for Mexico, beating out Tara (Nov. 12, 1961). An Air Force Hurricane Hunter mission is scheduled for Sandra on Friday afternoon.

Figure 1. VIIRS infrared satellite image of Hurricane Sandra taken at 3:15 pm EST November 25, 2015. At the time, Sandra was a Category 3 storm with 115 mph winds. Image credit: Dan Lindsey, NOAA/CIRA.

Figure 2. Latest satellite image of Sandra.

A rare Thanksgiving Day hurricane
Sandra is only the second Thanksgiving Day hurricane in modern records for the Atlantic or Eastern Pacific, and the strongest by far. The other hurricane was Hurricane Karl of 1980, which spun harmlessly as a minimal Category 1 hurricane far out in the central North Atlantic on Thanksgiving Day that year. Several other weaker storms have had NHC forecasters issuing advisories on Thanksgiving Day. This includes 1987’s Tropical Storm Keith, which struck Florida as a tropical storm on Wednesday, November 23, and persisted as a strong tropical storm east of Florida until midday Thanksgiving Day (November 24). In 1998, minimal Tropical Storm Nicole weakened to a depression east of Bermuda early on Thanksgiving Day (November 26), with advisories discontinued at 10 am EST. Nicole did get a new lease on life several days later, becoming a hurricane on November 30 and persisting to become one of just five Atlantic hurricanes on record during the month of December. In the hyperactive Atlantic season of 2005, Tropical Storm Delta roamed the eastern Atlantic on Thanksgiving Day (November 24). And in 2011, a weakening Tropical Storm Keith well out to sea in the eastern Pacific prompted advisories on Thanksgiving Day (November 24). Prior to the establishment of NHC as we know it, an unnamed tropical storm dissipated on Thanksgiving Day 1953 (November 26) well east of Bermuda. Hawaii takes the cake for the worst U.S. hurricane-related impacts during Thanksgiving Week: Hurricane Iwa passed near Kauai on Tuesday, November 23, 1982, during the run-up to the “super” El Niño of 1982-83. Iwa caused one death and inflicted $250 million in damage in Kauai.

Figure 3. Projected 5-day precipitation totals (rain and melted snow/sleet) for the period from 7 am EST Thursday, November 26, through Tuesday, December 1.

Thanksgiving travel troubles in store across the Central U.S.
Some of the biggest impacts from Sandra may occur with a prolonged heavy rain episode in the Southern Plains, increased by Sandra’s remnants. The strong upper-level low settling over the U.S. Southwest will help pull Sandra northeastward, and the storm’s moisture will flow atop a very shallow cold air mass that will spill across the Southern Plains later this week. Such setups involving Eastern Pacific hurricanes are notorious for giving the region some of its heaviest rains on record, but they are far more typical of September or October than late November. Flash flood watches are already in effect from far north Texas to southwest Illinois, and localized flooding may become a major travel headache. Rainfall totals of 5-10” are expected from Thursday through Monday across north Texas, southeast Oklahoma, and much of Arkansas. These rains will fall over areas that have been doused repeatedly over the last few months. With 50.75” of rain for the year through Wednesday, the Dallas-Fort Worth area may well break its all-time annual precipitation record of 53.54” (set in 1991), before November is done.

On the northwest edge of the heavy rain swath, there will be a parallel strip with low-level temperatures cold enough for widespread freezing rain, sleet, and/or snow, from Thanksgiving Day into Friday. An ice storm warning has been issued for parts of Texas, Oklahoma, and Kansas, with some places expected to get 0.5 - 1.0" of ice.

Stay safe, everyone, and have a great Thanksgiving!

Jeff Masters and Bob Henson


Unseasonable Sandra: Hurricane Threat for Mexico, Torrential Rain in Southern Plains

By: Bob Henson and Jeff Masters , 5:51 PM GMT on November 25, 2015

Holiday travel during the busy Saturday/Sunday Thanksgiving weekend across portions of the Southern Plains will get disrupted by a most unusual occurrence--flooding rains and a potential ice storm, enhanced by moisture from the strongest Eastern Pacific hurricane observed so late in the year. Declared a hurricane on Tuesday night, fast-strengthening Sandra is already making East Pacific history about 700 miles south of Cabo San Lucas. Sandra reached Category 2 strength in the National Hurricane Center’s 10 am EST Wednesday advisory, with top sustained winds estimated by satellite at 85 knots (100 mph). Sandra is the second-latest hurricane to form in the East Pacific since reliable satellite-based records began in 1971. Prior to Sandra, the strongest East Pacific hurricane so late in the year was 1983’s Winnie, which topped out on December 6 at 80 knots (about 90 mph). The king of November hurricanes in the East Pacific is 2011’s Kenneth, which attained top sustained winds of 125 knots (145 mph) on November 22--just two days before (U.S.) Thanksgiving Day.

Figure 1. Satellite image of Hurricane Sandra taken at 10 am EST November 25, 2015. At the image, Sandra was a Category 2 storm with 100 mph winds. Image credit: NASA/GSFC.

Even though it’s late November, conditions are unusually supportive for Sandra to continue intensifying into a major hurricane. A small eye has become evident on satellite imagery over the last few hours, with a compact zone of intense convection around it. Sea surface temperatures are at record highs for the time of year (29-30°C, or 84-86°F), and there is plenty of oceanic heat content below the surface (see Figure 2). Although Sandra is gradually moving into a region of higher vertical wind shear, the current values of 10 - 20 knots should allow continued strengthening. Things will change quickly by Thursday, however, as Sandra’s northwestward motion takes it into much stronger flow ahead of a powerful upper-level trough moving into the Southwest U.S. Cooler SSTs and higher shear will take its toll, weakening Sandra dramatically. There remains some spread in computer model guidance on Sandra’s intensity and track as it approaches the Mexican coastline, although a stronger, more intact Sandra would tend to recurve more quickly and further south due to greater influence of the upper-level steering flow. The 00Z ECMWF model brings Sandra into the Baja Peninsula as a very weak cyclone, while the 06Z runs of the HWRF, GFDL, and GFS models bring Sandra to the coast near or north of Mazatlan early Saturday as a stronger system, possibly a Category 1 hurricane. Hurricane or tropical storm watches or warnings may be issued as soon as Wednesday evening for parts of the Mexican coastline, and the Hurricane Hunters are on call to investigate Sandra on Friday afternoon. According to WU contributor Phil Klotzbach (Colorado State University), Sandra is on track to become the latest landfalling tropical cyclone on record for Mexico, beating out Tara (Nov. 12, 1961).

Figure 2. Oceanic heat content (in kilojoules per centimeter squared) along the path of Hurricane Sandra, beginning at 7 am EST Wednesday November 25. Sandra was over water with a lot of heat on Wednesday morning (yellow colors), but was forecast to move into a region of substantially less heat content by Wednesday night (12 hour forecast point over blue-green colors.) The oceanic heat content for Sandra is much lower than what Hurricane Patricia had to work with on October 23, 2015, when it rapidly intensified into a Category 5 storm with 200 mph winds. Image credit: NOAA/RAMMB.

A rare Thanksgiving Day hurricane
Assuming Sandra persists as a hurricane into Thursday as expected, it will be only the second Thanksgiving Day hurricane in modern records for the Atlantic or Eastern Pacific, and the strongest by far. The other was Hurricane Karl, which spun harmlessly as a minimal Category 1 hurricane far out in the central North Atlantic on Thanksgiving Day 1980. Several other weaker storms have had NHC forecasters issuing advisories on Thanksgiving Day. This includes 1987’s Tropical Storm Keith, which struck Florida as a tropical storm on Wednesday, November 23, and persisted as a strong tropical storm east of Florida until midday Thanksgiving Day (November 24). In 1998, minimal Tropical Storm Nicole weakened to a depression east of Bermuda early on Thanksgiving Day (November 26), with advisories discontinued at 10 am EST. Nicole did get a new lease on life several days later, becoming a hurricane on November 30 and persisting to become one of just five Atlantic hurricanes on record during the month of December. In the hyperactive Atlantic season of 2005, Tropical Storm Delta roamed the eastern Atlantic on Thanksgiving Day (November 24). And in 2011, a weakening Tropical Storm Keith well out to sea in the eastern Pacific prompted advisories on Thanksgiving Day (November 24). Prior to the establishment of NHC as we know it, an unnamed tropical storm dissipated on Thanksgiving Day 1953 (November 26) well east of Bermuda. Hawaii takes the cake for the worst U.S. hurricane-related impacts during Thanksgiving Week: Hurricane Iwa passed near Kauai on Tuesday, November 23, 1982, during the run-up to the “super” El Niño of 1982-83. Iwa caused one death and inflicted $250 million in damage in Kauai.

A banner year for Central and Eastern Pacific hurricanes
Assuming Sandra is our final tropical cyclone of 2015 in the Central and Eastern Pacific (not at all a sure thing in a year like this!), it will serve as a fitting capstone to an amazing year. The 16 hurricanes so far this year east of the International Date Line matches the record total set last year and in 1992. This year also ties with 1992 for the largest number of major hurricanes--10--although Sandra could push us above that mark. NHC’s Eric Blake notes that the two-year total of 32 Central and Eastern Pacific hurricanes in 2014 and 2015 beats out the two-year record of 27 set in 1992 and 1993.

Figure 3. Projected 5-day precipitation totals (rain and melted snow/sleet) for the period from 7 am EST Wednesday, November 25, through Monday, November 30.

Thanksgiving travel troubles in store across the central U.S.
Some of the biggest impacts from Sandra may occur with a prolonged heavy rain episode in the Southern Plains, increased by Sandra’s remnants. The strong upper-level low settling over the U.S. Southwest will help pull Sandra northeastward, and the storm’s moisture will flow atop a very shallow cold air mass that will spill across the Southern Plains later this week. Such setups involving Eastern Pacific hurricanes are notorious for giving the region some of its heaviest rains on record, but they are far more typical of September or October than late November. Flash flood watches are already in effect from far north Texas to southwest Illinois, and localized flooding may become a major travel headache. Rainfall totals of 5-10” are expected from Thursday through Monday across north Texas, southeast Oklahoma, and much of Arkansas. These rains will fall over areas that have been doused repeatedly over the last few months. With 50.75” of rain for the year through Tuesday morning, Dallas-Fort Worth area may well break its all-time annual precipitation record of 53.54” (set in 1991) before November is done.

On the northwest edge of the heavy rain swath, there should be a parallel strip with low-level temperatures cold enough for mostly light but widespread freezing rain, sleet, and/or snow, with an initial round from Thanksgiving Day into Friday and perhaps a second batch over the weekend as another lobe rotates around the sprawling upper-level low. Warm surfaces, and plenty of warm air at upper levels, may cut into this storm’s ability to cause high-impact winter weather, but frozen precipitation appears likely from eastern New Mexico, the Texas Panhandle, and northwest Oklahoma into eastern Colorado and much of Kansas and Nebraska, as well as the higher elevations of Colorado and New Mexico. An ice storm warning may be issued for parts of the northwest half of Oklahoma as the event draws closer.

Stay safe, everyone, and have a great Thanksgiving!

Bob Henson and Jeff Masters

Hurricane Winter Weather Flood

Late-Season Tropical Storm Sandra Could Strike Mexico and Drench Texas

By: Jeff Masters and Bob Henson , 4:05 PM GMT on November 24, 2015

Tropical Storm Sandra formed on Tuesday morning in the record-warm Pacific waters off the south coast of Mexico, about 570 miles south of Manzanillo. Sandra joins last week's Tropical Storm Rick as one of the latest-forming tropical storms in the history of the Eastern Pacific. Since accurate records began in 1949 (with higher-quality satellite records beginning in 1971), the Eastern Pacific has seen only six tropical storms form after November 18: December 5, 1983 (Winnie), November 27, 1971 (Sharon), November 27, 1951 (Unnamed), November 24, 2015 (Sandra), November 20, 2011 (Kenneth), and November 19, 2015 (Rick). None of these storms hit land. If Sandra hits land, it will be the latest landfalling Eastern Pacific storm on record.

Satellite images on Tuesday morning showed that Sandra had a large and steadily organizing area of heavy thunderstorms. Steering currents favor a path to the west or west-northwest parallel to the coast and far enough offshore to prevent heavy rains in Mexico through Thursday. On Friday, a trough of low pressure passing to the north of Sandra will turn the storm to the north and northeast, but will also bring high wind shear, weakening the storm as it approaches the tip of the Baja Peninsula.

Conditions are quite favorable for Sandra to intensify over the next couple of days, with record-warm sea surface temperatures of 29-30°C (84-86°F) and wind shear of less than 10 knots beneath an upper-level high arcing around the storm. The official NHC forecast issued at 10 am EST Tuesday brings Sandra to Category 2 strength, with peak winds of 100 mph by Thursday. NHC’s Rapid Intensification Index shows roughly a 50-50 chance that Sandra will strengthen by at least 30 knots in the next 24 hours. If Sandra does reach Category 2 strength, it will be the strongest Eastern Pacific hurricane known to exist so late in the year. All of the six cyclones above were tropical storms or Category 1 hurricanes except for Kenneth, which hit Category 4 strength on November 24, 2011. Kenneth is the latest-occurring major hurricane in Eastern Pacific records.

Figure 1. Latest satellite image of Sandra.

With Sandra virtually certain to be a tropical storm or hurricane on Thanksgiving Day, this year will mark the first time NHC has ever had to issue Thanksgiving Day advisories for an Eastern Pacific named storm. However, NHC has issued Thanksgiving Day advisories for Atlantic storms on a number of occasions. The last time was November 24 during the year--you guessed it--2005, during the insane Hurricane Season of 2005, when Tropical Storm Delta was active during Thanksgiving weekend in the far eastern Atlantic.

Sandra may complicate heavy rain threat over Southern Plains
The biggest impacts from Sandra may occur from Texas to Arkansas, where a prolonged heavy rain episode late this week seems likely to be enhanced by Sandra’s remnants. A strong upper-level low settling over the U.S. Southwest will help pull Sandra northeastward, and the storm’s moisture will flow atop a very shallow cold air mass that will spill across the Southern Plains later this week. Such setups involving Eastern Pacific hurricanes are notorious for giving the region some of its heaviest rains on record, but they are far more typical of September or October than late November. Localized flooding may become a major travel headache, as rainfall totals of 3-8” are expected from Thursday through Sunday over central and north Texas, southeast Oklahoma, southern Missouri, and northwest Arkansas (see Figure 2 below). These rains will fall over areas that have been doused repeatedly over the last few months. With 50.75” of rain for the year through Tuesday morning, Dallas-Fort Worth area may well break its all-time annual precipitation record of 53.54” (set in 1991) before November is done.

On the northwest edge of the heavy rain swath, there should be a parallel strip with low-level temperatures cold enough for mostly light but widespread freezing rain, sleet, and/or snow, with an initial round from Thanksgiving Day into Friday and perhaps a second batch over the weekend as another lobe rotates around the sprawling upper-level low. Frozen precipitation is most likely from the Texas Panhandle and northwest Oklahoma across much of Kansas to eastern Nebraska.

Wunderblogger Steve Gregory has a new Monday afternoon post, Stormy Thanksgiving / Potential Flash Flooding and Blizzard Conditions for Texas.

Jeff Masters and Bob Henson

Figure 2. Projected 5-day precipitation totals (rain and melted snow/sleet) for the period from 7 am EST Tuesday, November 24, through Sunday, November 29.

Hurricane Extreme Weather Winter Weather

Eastern Pacific's Invest 91E A Threat to Mexico

By: Jeff Masters and Bob Henson , 5:22 PM GMT on November 23, 2015

An area of disturbed weather (Invest 91E) is approaching tropical depression status in the record-warm Pacific waters off the south coast of Mexico, about 425 miles south of Acapulco. Satellite images on Monday morning showed that 91E had a large and expanding area of heavy thunderstorms with a pronounced rotation. The 7 am EST Monday run of the SHIPS model predicted that 91E would be over record-warm ocean waters near 30°C (86°F) and under light wind shear around 10 knots through Friday, which should allow the storm to develop into Tropical Storm Sandra by Wednesday. In their 7 am EST Tropical Weather Outlook, NHC gave 91E 2-day and 5-day odds of development of 90%. The HWRF and GFDL intensity models have consistently shown the potential for this storm to become a hurricane by late in the week. Steering currents favor a path to the west or west-northwest parallel to the coast and far enough offshore to prevent heavy rains in Mexico through Thursday. On Friday, a trough of low pressure passing to the north of 91E will turn the storm to the north and northeast, and 91E will likely make landfall in Mexico this weekend, passing near the tip of the Baja Peninsula. Those of you planning to spend Thanksgiving weekend in the Cabo San Lucas area you should anticipate the possibility of a tropical storm affecting your weather.

Figure 1. Latest satellite image of Invest 91E.

If Sandra does form this week, it will join last week's Tropical Storm Rick as one of the latest-forming tropical storms in the history of the Eastern Pacific. Since accurate records began in 1949 (with higher-quality satellite records beginning in 1971), the Eastern Pacific has seen only five tropical storms form after November 18: December 5, 1983 (Winnie), November 27, 1971 (Sharon), November 27, 1951 (Unnamed), November 20, 2011 (Kenneth), and November 19, 2015 (Rick). None of these storms hit land. If 91E becomes a tropical storm and hits land, it will be the latest landfalling Eastern Pacific storm on record. This year has also beaten the onset year of the 1997-98 El Niño in terms of the span from the earliest to latest tropical cyclone in the Northeast Pacific. The season’s first storm of 2015, Andres, formed on May 28, four days earlier than Andrea in 1997. The last NE Pacific storm of 1997, also named Rick, formed on November 7, although it was followed on December 2 by Tropical Storm Paka in the Central Pacific. (Thanks to WU member Mark Cole for this statistic.)

Figure 2. MODIS image of Typhoon In-fa taken at 02:00 UTC November 23, 2015. At the time, In-fa was a Category 2 storm with 105 mph winds. Image credit: NASA.

Typhoon In-fa no threat to land
In the Western Pacific, Category 2 Typhoon In-fa is tracking to the north on a path that is expected to keep the storm from striking any land areas as a typhoon. On Saturday, In-fa topped out as a Category 4 storm with 130 mph winds, becoming the record-shattering 24th Category 4 or stronger tropical cyclone in the Northern Hemisphere in 2015. According to wunderblogger Dr. Phil Klotzbach's Twitter feed, the previous record was eighteen such storms in 1997 and 2004. On Sunday, In-fa  brought the number of typhoon days in the Northwest Pacific to 104.5, the most on record for the basin to date (previous record: 103 in 1997.)

The Atlantic is quiet with no tropical cyclone formation expected for the next five days.

Potent mid-autumn snowstorm socks Midwest
Parts of the Chicago area saw their biggest snow on record for so early in the season on Friday and Saturday, courtesy of a fast-moving storm that left a compact but focused swath of snow from South Dakota to Michigan. It was the parting shot of a powerful sequence of upper-level lows that caused a variety of extreme weather throughout the week, from tornadoes in Kansas and Texas to destructive winds in Washington.

The tight focus of the snow-making machine led to big contrasts in accumulations over fairly small areas. Northwest of downtown, Chicago’s O’Hare International Airport picked up 11.2”, which made it the heaviest snowstorm ever recorded for Chicago so early in the year and the second-heaviest November storm behind 12.0” on Nov. 25-26, 1895. However, the city center got far less snow: only about 1” was recorded downtown, according to the National Weather Service. Likewise, the Rockford area west of Chicago saw totals ranging from less than 9” to 18”. As in Chicago, Rockford’s official storm total of 8.8” ranked as the heaviest on record so early in the year and the second-heaviest for November, behind 9.5” on Nov. 6-7, 1951.

Figure 3. Except for a few obscuring clouds over southern Michigan, this weekend’s swath of snow remained clear in a GOES visible satellite image at 1630Z (11:30 am EST) Monday, November 23, 2015.

Figure 4. Clear skies atop the snow swath shown in Figure 3 allowed temperatures to plummet on Saturday night. Shown are the low temperatures for the 24 hours ending on Sunday morning, November 22, 2015. Widespread lows below 10°F occurred across the snow-covered areas, with a few below-zero readings evident (purple dots). Image credit: Midwestern Regional Climate Center.

Figure 5. A band of more than 12” of snow stretched across southern Michigan and northern Indiana, with 15.5” falling at the NWS Detroit/Pontiac office--the heaviest total recorded at that office since it opened in 1994. At my backyard weather station at Dunham Lake, Michigan, we had 15" inches of snow in 15 hours on Saturday--a pretty shocking way to get our first measurable snow of the season! This is one of the top-five snowstorms of my life here in Michigan, and the second one this year. On February 2, we had another 15" snowstorm here. --Jeff Masters

El Niño notches another record-high weekly value
The record-setting El Niño event of 2015 continues to impress. NOAA reported today that last week’s departure from average sea-surface temperature across the benchmark Niño3.4 region was +3.1°C, the highest weekly value on record in NOAA data going back to 1990. The 1997-98 El Niño maxed out at a weekly Niño3.4 anomaly of +2.8°C for the week centered on November 26, 1997. There’s an increasing westward focus to this El Niño event, as the current anomaly over the Niño4.0 region (which straddles the international date line, from 160°E to 150°W longitude) is up to 1.8°C, almost as warm as the Niño1+2 region (just off the South American coast), which currently sits at 2.1°C. Since the Niño1+2 region remains well above average, this event does not qualify as an El Niño Modoki, which can produce quite different U.S. effects than a “classic” El Niño. For more background on El Niño science and impacts, see our dedicated WU microsite.

Wunderblogger Steve Gregory has a new Monday afternoon post, Stormy Thanksgiving / Potential Flash Flooding and Blizzard Conditions for Texas.

Jeff Masters (tropics), Bob Henson (snow and El Niño)

Hurricane Extreme Weather El Niño

Carbon Dioxide Bidding Farewell to 400-ppm Benchmark

By: Bob Henson , 5:18 PM GMT on November 20, 2015

On an otherwise unremarkable day last week--November 11, 2015 (noted mainly for being Veterans Day in the U.S.)--a crucial milestone in global climate was quietly transcended. The daily average concentration of carbon dioxide in the air that day at Hawaii’s Mauna Loa Observatory was 399.68 parts per million. On November 12 it rose to 401.64 ppm, and it’s quite possible that we’ll never see another day in our lives with the daily Mauna Loa CO2 reading below 400 ppm. Greenhouse gases have been building in our atmosphere for more than a century, so this news doesn’t come as a shock so much as a reminder of what our continued use of fossil fuels is doing to the atmosphere. The data also serve as a prelude to the upcoming United Nations climate talks in Paris, which face some unexpected obstacles (see below) as a result of the city’s terrorist attacks of November 13.

Figure 1. Hourly and daily averages of atmospheric carbon dioxide as measured at Mauna Loa Observatory for the week of November 12-18, 2015. Image credit: Scripps/The Keeling Curve.

If it seems like you heard the news about the atmosphere reaching 400 ppm quite a while ago, you can attribute your deja vu to the seasonal cycle. Figure 2 (below) shows what’s been going on. The 400-ppm mark was first reached in May 2013--but only for a few days, during the annual peak of atmospheric CO2. Along with the year-on-year rise due to fossil-fuel use, CO2 ebbs and flows in the atmosphere each year as vegetation grows and dies back in the Northern Hemisphere (where the majority of the world’s plant life is located). In 2014, the daily Mauna Loa readings stayed above 400 ppm for more than three months. This year they rose above 400 ppm even longer, again dipping below 400 ppm in August before climbing back above the benchmark this month.

Ordinarily, we might expect one more northern summer with CO2 values below 400 ppm, but El Niño could prevent that. A strong El Niño event, like the one now under way, tends to produce drought in some of the world’s most heavily forested areas, such as Indonesia. Averaged across the globe, this temporarily reduces the total amount of CO2 soaked up by Earth’s vegetation. In addition, the large fires common in drought-stricken areas pour even more CO2 into the air. Based on this prospect, Ralph Keeling, who directs the CO2 measurement program at Mauna Loa for the Scripps Institute of Oceanography, made a fairly bold prediction on October 21: “By sometime in the next month or two, CO2 will again rise above 400 ppm. Will daily values at Mauna Loa ever fall below 400 ppm again in our lifetimes? I’m prepared to project that they won’t, making the current values the last time the Mauna Loa record will produce numbers in the 300s.”

Figure 2. CO2 measurements from Mauna Loa Observatory for (top to bottom) the past six months, the past two years, and since the observatory was established in 1958. The final panel shows the Mauna Loa record juxtaposed with CO2 readings deduced from air trapped in ice cores. The ice-core evidence shows that carbon dioxide waxed and waned with a number of ice ages, but the current values near 400 ppm are far greater than any peaks observed in at least the last 800,000 years--and probably much further back than that. Image credit: Scripps/The Keeling Curve.

What next?
Figure 1 shows that the hourly readings at Mauna Loa can vary quite a bit. It’s possible we’ll see more days this month with hourly readings dipping below 400 ppm, as they did on November 18. However, even these hourly readings should remain firmly above 400 ppm within a few weeks. If Keeling’s prediction is accurate, daily readings may stay above 400 ppm in 2015 and for many years thereafter. It’s also still possible that a few hours or even several days might manage to dip just below 400 ppm in mid-2016.

There are other CO2 measurement facilities around the world, although the Mauna Loa record is the one most commonly cited, with its high quality, pristine location, and longevity (Keeling’s father, Charles David Keeling, began regular measurements there in 1958). Different measuring sites will see the 400-ppm mark in their rear-view mirrors at slightly different times, due to local atmospheric variations, but there is no doubt where the global atmosphere is headed. I asked Ralph Keeling on Wednesday for his latest thoughts.

“It's too early to be 100% certain, but I agree that it's starting to look like we are already over 400 ppm for this year, with the last daily and weekly values below 400 ppm occurring earlier this month,” Keeling said. “It also looks like the November monthly average will also be above 400 ppm.”

Climate-change deniers and contrarians typically look beyond CO2 measurements when crafting their talking points, but a few misunderstandings about the role of carbon dioxide still crop up--many of them skillfully rebutted by the website “A possible misconception about the Mauna Loa CO2 record is that the overall increase is influenced by emissions from the volcano,” Keeling told me. “In fact, the volcanic effects are very small and are easily filtered out, like static on a radio signal. Dozens of stations around the world show essentially identical long-term trends, including a record from the South Pole also going back to the 1950s.  The CO2 at these stations might be a little higher or lower than Mauna Loa in a particular season or averaged over the calendar year. But the upward trends are all pretty similar. The rise is therefore clearly a global phenomenon.”

What it means for the Paris climate talks
The 400-ppm news comes just as Earth is experiencing a heat wave fueled by the long-term rise in greenhouse gases and goosed by El Niño. NOAA announced on Wednesday that global temperatures in October 2015 showed the largest departure from the long-term average for any month going back to 1880. The UK Met Office now predicts that global temperature in 2015 will likely end up at least 1°C warmer than the preindustrial average. This would put our planet halfway to the 2°C warming that’s long been viewed by many scientists and policy experts as a level that significantly raises the odds of major climate disruption (although there is nothing magic about 2°C; a smaller rise could still have serious consequences). A brief video from the journal Nature, released on Thursday, serves as a quick guide to the origin and significance of the 2°C goal.

All of these happenings underscore the importance of the two-week-long meeting in Paris that begins on November 30. This is COP21, the 21st annual Conference of the Parties to the United Nations Framework Convention on Climate Change, which was signed in 1992 and ratified by the United States and all other UN members. There has been an unprecedented level of cooperation among the world’s leading carbon-emitting nations in the lead-up to COP21, which raises the odds that a workable agreement for carbon reduction just might be achievable. In contrast to the Kyoto Protocol, which failed to gain support from the world’s two largest carbon emitters--the United States and China--it’s expected that any deal arising from Paris will hinge on voluntary commitments (dubbed “intended nationally determined contributions”, or INDCs) that have already been submitted by more than 160 nations representing more than 90% of global emissions. In an upcoming post, we’ll take a closer look at what to expect and what to watch for as COP21 unfolds. WU climate blogger Dr. Ricky Rood has already filed a series of posts that lay out important context ahead of the Paris meeting. I attended the ill-fated Copenhagen meeting in 2009 (COP15) and came away profoundly discouraged at the lack of progress there. This time around, I am cautiously optimistic that a truly global deal will be struck, although I’m not confident that it will be enough to prevent 2°C of warming.

Figure 3. One of the major protest marches held during the Copenhagen climate summit in December 2009. Image credit: Bob Henson.

In wake of attacks, a global climate march gets new attention
Several experts involved with the upcoming UN meeting have speculated that global leaders now have even more incentive to make the talks a success in the wake of the deadly November 13 attacks in Paris. At the same time, the French government announced on Wednesday that massive climate marches planned for Paris on November 29 and December 12 would not be allowed, due to the heightened state of alert following the deadly attacks of November 13. Organizers led by and have responded by intensifying their efforts toward a Global Climate March, scheduled for the weekend of November 28-29. More than 2000 events are on tap in towns and cities around the world. You can see what’s happening near you by using the interactive tool at this Guardian article.

Bob Henson

Climate Change Politics Climate Change

Destructive Windstorm Rips across Northwest U.S.; TS Rick Forms in Northeast Pacific

By: Bob Henson and Jeff Masters , 5:55 PM GMT on November 19, 2015

One of the most widespread and damaging bouts of high wind to strike the Northwest U.S. in years tore down trees and power lines and knocked vehicles off roadways from Washington to the northern Great Plains from Tuesday into Wednesday. At one point, high wind warnings covered nearly 1 million square kilometers, or more than 10% of the contiguous United States (thanks to Stu Ostro at The Weather Channel for this tidbit). Washington governor Jay Inslee declared a state of emergency for all counties in the state on Wednesday. According to, at least four deaths were reported, and more than 1 million people in several states have been affected by power outages, in some cases for hours or days. Avista, the utility that serves the Spokane, Washington, area, said the windstorm was "the most devastating natural disaster the utility has faced in its 126 year history," with more than 100,000 customers still without power as of Thursday afternoon (thanks to WU member fred37 for calling this to our attention). A sampling of the most impressive wind reports:

Spokane, WA: 71 mph. This was the strongest wind ever recorded at Spokane International Airport apart from thunderstorms.
Mission Ridge Ski Area, WA: 137 mph
Colburn, ID (5 miles west): 101 mph
Chadron, NE: 75 mph

Figure 1. Eastbound traffic lanes, right, on Interstate 90 are dampened by wind-driven waves from the south as the floating bridge calms Lake Washington to the north, left, Tuesday, Nov. 17, 2015, in Seattle. Image credit: AP Photo/Elaine Thompson.

Figure 2. Jay Bly checks out the damage to his home in Spokane, Wash., Wednesday, Nov. 18, 2015, after a Norway spruce fell on his house the day before. Image credit: Colin Mulvany/The Spokesman-Review via AP.

Figure 3. Wind trace from atop the Mesa Laboratory at the National Center for Atmospheric Research in Boulder, CO, from 7:49 am MDT Tuesday, November 18, 2015, to 7:49 am MDT Wednesday. The peak gust was 94.4 mph just after 7 am Wednesday. Image credit: NCAR/RAL Real-Time Weather Data.

The wind-prone areas of Colorado’s Front Range, between Interstate 25 and the foothills of the Rockies, got hammered by this windstorm, with a number of car windows left shattered. Wind gusted to 95 mph in Lyons; 94 mph at the National Center for Atmospheric Research’s Mesa Laboratory, which sits just above Boulder; and to 102 mph at (fittingly) the National Wind Technology Center, a few miles to the south of Boulder. At Colorado State University in Fort Collins, a gust to 77 mph was the second-strongest since records began in 1997, behind only 84 mph on December 30, 2008, according to Dan Lindsey (CSU/CIRA). I don’t have a wind report from my own place in Louisville, just east of Boulder, but my frame house was groaning during the peak of the storm!

El Niño not strongly linked with major Northwest windstorms
Boulder is one of the largest U.S. cities prone to extreme downslope winds (warm chinooks and cold boras). An informal catalog of high wind events in Boulder since the 1960s, maintained by NOAA’s Earth System Research Laboratory, shows that major windstorms have occurred in both El Niño and La Niña years. The “super” El Niño winters of 1982-83 and 1997-98 were both skimpy on high-wind events in Boulder. Likewise, El Niño is not typically associated with damaging windstorms over the Northwest U.S. Data compiled by the University of Washington’s Cliff Mass show that the eight years from 1860 to 2000 associated with the most destructive Pacific Northwest windstorms all had Niño3.4 anomalies between +1.0°C and -1.0°C for the November-to-February period. In other words, these were either neutral, weak El Niño, or weak La Niña years. “Big windstorms AVOID strong El Nino years. Similar to vampires and garlic,” says Mass. “But there can be moderate storms in El Nino years and it appears that the very strongest years (like 97-98) had plenty of coastal storms.” Although eastern Washington experienced some of its highest winds on record this week, Mass dubbed the winds in the Puget Sound area of western Washington (gusts to 30-45 mph over land and 40-60 mph over water) “substantial but not record breaking.”

The culprit for this large-scale high wind event was an extremely powerful jet stream (see Figure 4 below) that arrived in Washington from the west, then angled east-southeast as it arced toward the Plains north of a strong ridge of high pressure off the California coast. The anticyclonic orientation of the flow favored downward motion that allowed very strong upper-level winds to mix toward the surface, especially in the lee of mountain ranges. Ahead of this strong jet, the powerful upper-level storm that fueled severe weather over the central and southeastern United States over the last several days has lifted northeast into Canada, leaving behind a front that remains remarkably well-defined on satellite near the Appalachians (see Figure 5 below).

Figure 4. WunderMap depiction of winds at 12Z (7:00 am EDT) Thursday, November 19, 2015, at the 200-millibar level, or about 38,000 feet. A powerful jet continues to arc across the western United States.

Figure 5. Visible GOES-13 satellite image from 1600Z (11:00 am EDT) Thursday, November 19, 2015. Image credit: NOAA-NASA Goes Project.

Rainy night in Nunavut
The channel of warm, moist southerly flow ahead of the front and upper-level storm shown in Figures 4 and 5 will bring a rare night of November rain to Iqaluit, the capitol of Nunavut, Canada. Located about 200 miles south of the Arctic Circle (see Figure 6), Iqaluit averages 59” of snow but just 0.03” of rainfall from November through April. Its average daily high on November 19 is 12°F. On Thursday night, after a sunset at 2:26 pm, Iqaluit is expecting rain and temperatures in the upper 30s.

Figure 6. Departures from average temperature at 12Z Thursday, November 19, 2015. Image credit: Climate Reanalyzer/University of Maine.

Late-season Tropical Storm Rick forms in Eastern Pacific
Tropical Storm Rick formed on Thursday morning in the record-warm Pacific waters off the southwest coast of Mexico, becoming one of the latest-forming tropical storms in the history of the Eastern Pacific. Since accurate records began in 1949 (with higher-quality satellite records beginning in 1971), the Eastern Pacific has seen only four tropical storms form after November 18: December 5, 1983 (Winnie), November 27, 1971 (Sharon), November 27, 1951 (Unnamed), and November 20, 2011 (Kenneth.) None of these storms hit land. Rick is also not expected to hit land; after a two-day period of intensification on Thursday and Friday, wind shear will increase over Rick this weekend, likely destroying the storm by Monday. Both the GFS and European models are advertising the possibility of another tropical storm forming in a similar location early next week.

Figure 7. MODIS image of Typhoon In-fa taken at 03:00 UTC November 18, 2015. At the time, In-fa was a Category 1 storm with 75 mph winds. Image credit: NASA.

Typhoon In-fa expected to pass south of Guam
In the Western Pacific, Typhoon In-fa is tracking west-northwest on a path that is expected to take the storm about 200 miles south of Guam on Saturday. In-fa became a typhoon on Wednesday unusually far to the south--at 5.8°N. According to wunderblogger Dr. Phil Klotzbach, this is the farthest south that a typhoon has formed since Typhoon Bopha of 2012 (3.8°N). In-fa is not expected to hit any land areas, and the Joint Typhoon Warning Center forecasts that the storm will top out at Category 3 strength this weekend.

The Atlantic is quiet with no tropical cyclone formation expected for the next five days.

Bob Henson (windstorm), Jeff Masters (tropical)

Winter Weather Extreme Weather Hurricane

October 2015: Earth's Warmest Month on Record by a Huge Margin

By: Jeff Masters , 4:54 PM GMT on November 18, 2015

Earth’s surface temperature has surged high into uncharted territory, thanks to a record-strength El Niño event combined with the long-term rise in temperatures due to human-caused global warming: October 2015 was Earth’s warmest month on record by a huge margin, according to data released by NOAA's National Centers for Environmental Information (NCEI) on Wednesday. October 2015 was the second consecutive month with a new all-time warmest month record: September 2015 previously held the record for the largest positive departure of temperature from average of any month among all 1630 months in the historical record that began in January 1880. As shown in the table below, October 2015's 0.98°C (1.76°F) departure from the 20th Century average beat the next ten runners-up by an unusually large margin, underscoring how unusual and extreme the current surge in global temperatures is. NASA also rated October 2015 as the warmest month in the historical record by a large margin, again defined as the largest positive departure from average (note that in an absolute sense, Earth's warmest month is July, but NOAA and NASA do not keep track of global temperature records in an absolute sense.) October 2015's warmth makes the year-to-date period (January - October) the warmest such period on record, according to both NOAA and NASA. October 2015 was the sixth consecutive month a monthly high temperature record has been set in NOAA's database, and the eighth month of the ten months so far in 2015. The potent El Niño event in the Eastern Pacific that crossed the threshold into the "strong" category in early July continued to intensify into mid-November. Strong El Niño events release a large amount of heat to the atmosphere, typically boosting global temperatures by at least 0.1°C. This extra bump in temperature, when combined with the long-term warming of the planet due to human-caused emissions of heat-trapping gases like carbon dioxide, makes it virtually certain that 2015 will be Earth's second consecutive warmest year on record. The lingering warmth from El Niño is likely to make 2016 a good bet to exceed even 2015's warmth.

NOAA's top ten warmest global monthly departures from the 20th Century average:
1) 0.98°C, Oct 2015
2) 0.91°C, Sep 2015
3) 0.89°C, Mar 2015
4) 0.88°C, Feb 2015
4) 0.88°C, Jan 2007
6) 0.87°C, Aug 2015
6) 0.87°C, Jun 2015
8) 0.86°C, Feb 1998
9) 0.85°C, May 2015
10) 0.85°C, Mar 2010

Figure 1. Departure of temperature from average for October 2015, the warmest October for the globe since record keeping began in 1880. Record warmth was observed across the entire southern half of Australia, part of southern and southeastern Asia, much of central and southern Africa, most of Central America and northern South America, and parts of western North America. Record warmth was also over much of the world's oceans. This includes the Pacific waters near the Mexican coast, where Hurricane Patricia exploded into the most intense Western Hemisphere hurricane on record on October 23, with 200 mph winds. Record warm waters were also observed over the portion of the Arabian Sea where Category 4 Tropical Cyclone Chapala and Category 3 Megh tracked in October--the first time two major tropical cyclones had ever been observed in the Arabian Sea in the same year. Record warm waters were also observed around Hawaii, where the warm waters caused the worst coral bleaching episode in Hawaii's history, which will likely result in a large-scale die-off of coral. A loss of 10 - 20% of all coral worldwide is expected due to the global bleaching event currently underway, due to the extensive record-warm ocean temperatures worldwide. Image credit: National Centers for Environmental Information (NCEI) .

Figure 2. Departure of the global surface temperature from average for the year-to-date period January - October, for all years from 1880 to 2015. This year is on pace to easily beat last year as the warmest year on record. Image credit: NOAA.

Global satellite-measured temperatures in October 2015 for the lowest 8 km of the atmosphere were the warmest October readings in the 37-year record, according to the University of Alabama Huntsville (UAH), and were the 2nd warmest on record, according to RSS. The lowest 8 km of the atmosphere heats up dramatically in response to moderate to strong El Niño events, with a time lag of about six months.

Three billion-dollar weather disasters in October 2015
Three billion-dollar weather-related disasters hit the Earth last month, according to the October 2015 Catastrophe Report from insurance broker Aon Benfield: flooding in South Carolina of at least $2 billion, $4.2 billion in damage from China's Typhoon Mujigae, and $1 billion in damage from flash flooding in France. With 21 billion-dollar weather disasters through October 2015, Earth is on pace for a below-average number of these disasters, compared to the average of 28 recorded during the previous 10-year period, 2005 - 2014.

Disaster 1. Typhoon Mujigae hit the Philippines as a tropical storm on October 2 before rapidly intensifying and striking China on October 4 as a Category 3 storm. Mujigae killed two in the Philippines and at least 20 in China. Economic losses in Philippines were estimated at $1.3 million, and were $4.2 billion in China, making Mujigae the costliest tropical cyclone of 2015. In this image, we see a rapidly intensifying Typhoon Mujigae approaching China at 03:05 UTC October 3, 2015. Image credit: NASA.

Disaster 2. Torrential 1-in-1000 year rains of over two feet, associated with a plume of moisture wrapping around Hurricane Joaquin, brought tremendous flooding across much of South Carolina during the first week of October. At least 21 people were killed, and damage was conservatively estimated at $2.0 billion, including $300 million in damage to crops. In this photo, we see a church surrounded by flood waters on October 5, 2015 in Columbia, South Carolina. Image credit: Sean Rayford/Getty Images.

Disaster 3. At least 19 people were killed along the southeast coast of France by a flash flood on October 3 - 4. Cannes received a record 107 mm (4.21”) in just one hour; the previous one-hour record was 70 mm (2.76”). In this photo, we see a man walking past damaged cars in Mandelieu-la-Napoule, southern France, on October 5, 2015. Cars are often stacked in this manner in the aftermath of flash floods, as was the case during the catastrophic Rapid City, SD, flood of 1972 (scroll page for photo). Image credit: Anne-Christine Poujoulat/AFP/Getty Images.

Arctic sea ice comes in at 6th lowest October extent on record
Arctic sea ice extent during October 2015 was the 6th lowest in the 36-year satellite record, according to the National Snow and Ice Data Center (NSIDC).

Notable global heat and cold marks set for October 2015
Hottest temperature in the Northern Hemisphere: 46.0°C (114.8°F) at Bassora Airport, Iran, October 3.
Coldest temperature in the Northern Hemisphere: -60°C (-76.0°F) at Geo Summit, Greenland, October 24. This is a new record of minimum temperature in the Northern Hemisphere for the month of October.
Hottest temperature in the Southern Hemisphere: 48.4°C (119.1°F) at Vredendal, South Africa, October 27. This is a new world record of maximum temperature for the month of October.
Coldest temperature in the Southern Hemisphere: -72.3°C (-98.1°F) at Vostok, Antarctica, October 22.

Major stations that set (not tied) new all-time heat or cold records (for any month) in October 2015
Nevis Airport (Saint Kitts and Nevis) max. 34.1°C, 2 October
Canefield Airport (Dominica) max. 35.5°C,  3 and 4 October:  new national record high for Dominica
Gustavia (Saint Barthelemy, France) max. 35.5°C,  5 October: new territorial record high for Saint Barthelemy
Sal (Cape Verde) max. 36°C, 5 October
Peixe (Brazil) max. 41.4°C,  5 October
Picos (Brazil) max. 41.5°C, 5 October; broken again with 41.9°C on 21 October
Januaria (Brazil) max. 41.3°C,  5 October
Monte Azul (Brazil) max. 40.7°C,  5 October
Posse (Brazil) max. 39.1°C,  5 October
Aragarcas (Brazil) max. 42.6°C, 6 October
Xavantina (Brazil) max. 42.3°C, 6 October
Golden Rock Airport (Saint Kitts and Nevis) max. 34.1°C, 6 October
The Valley (Anguilla,United Kingdom) max. 34.2°C, 10 October:  new territorial record high for Anguilla;  this was broken on 11 October with a reading of 34.4°C (but this reading is suspect)
Pedro Afonso (Brazil) max. 40.9°C, 17 October
Palu (Indonesia) max. 38.5°C,  20 October
Pirapora (Brazil) max. 40.8°C, 21 October
Montes Claros (Brazil) max. 39.6°C, 21 October
Maripasoula (French Guiana, France) max. 37.5°C, 21 October
Saint Laurent du Moroni (French Guiana, France) max. 37.8°C, 22 October: new territorial record high for French Guiana
Saint Georges de L'Oyapock (French Guiana, France) max. 37.0°C, 22 October
Paracatu (Brazil) max. 40.2°C, 22 October
Arinos (Brazil) max. 42.3°C, 22 October
Peixe (Brazil) max. 41.5°C,  22 October
Monte Azul (Brazil) max. 41.1°C, 22 October
Taua (Brazil) max. 38.8°C,   22 October
Posse (Brazil) max. 39.2°C,  22 October
Semarang Airport (Indonesia) max. 39.5°C, 28 October: Tied national record high for Indonesia
Vredendal (South Africa) max. 48.4°C, 27 October

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

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

Jeff Masters

Climate Summaries

Springtime in November: Tornadoes Rake High Plains from Nebraska to Texas

By: Bob Henson and Jeff Masters , 6:46 PM GMT on November 17, 2015

The latest tornado outbreak on record west of the 100th meridian left damage strewn late Monday across parts of western Kansas and the Oklahoma and Texas Panhandles. The tornadoes emerged from a batch of long-lived supercell thunderstorms spawned by a very strong upper-level low that encountered near-record levels of atmospheric moisture for mid-November. The same upper-level storm has plastered the southern Rockies with heavy snow and produced blizzard conditions over parts of the High Plains, but the tornado outbreak was far more exceptional for the location and time of year. As of Tuesday morning, the NOAA Storm Prediction Center had logged an amazing 41 tornado reports. Many of these are likely to be multiple reports of the same tornado, so the final count may well drop, but it is clear that a remarkable event unfolded. Based on photos via social media, several of the tornadoes were large “wedges.” A Halliburton oil-field servicing plant was largely destroyed by a tornado east of Pampa, Texas, according to the county sheriff’s office. Nobody was in the building at the time, and chemicals and gas leaks produced by the tornado strike have reportedly been contained. Damage reports from this and other tornadoes on Monday are summarized in a roundup. For a dramatic time lapse of the Pampa storm, see the Twitter clip from JR Hehnly embedded with permission at the bottom of this post.

Figure 1. This tornado was photographed at 6:43 p.m. on Monday, November 16, 2015, just north of Groom, TX, by Quincy Vagell ( The tornado was first visible at 6:39 p.m. and on the ground for quite some time after. “Downed telephone poles/wires cut my chase short,” he said. A prior tornado from the same storm produced considerable damage south of Pampa. Image credit: Quincy Vagell, @stormchaserQ.

Much like last week’s central U.S. system, which produced tornadoes over Iowa, Monday’s upper-level storm arrived on a powerful midlatitude jet stream that’s kept weather features moving quickly across the nation over the last few days. This week’s upper storm is quite energetic, as evidenced by the tornado that struck on Sunday near Denair, California. Another key to Monday’s events is the unusually moist air mass brought up from the Gulf of Mexico ahead of both systems. Sea-surface temperatures are above average throughout the tropical and subtropical North Atlantic, with near-record values 1-2°C above average covering most of the Gulf of Mexico and Northwest Atlantic. Moisture evaporating from these warm waters flowed into the southern Great Plains on Monday in an extremely juicy airmass. Dewpoint temperatures rose into the 55-60°F range beneath a zone of very strong upper-level forcing and vertical wind shear. This setup favored the development of discrete supercell thunderstorms--the kind most likely to produce strong tornadoes--for several intense hours, until a Pacific cold front barrelled across the region after dark. The tornado threat then declined, as a north-south squall line swept across Oklahoma and north central Texas during the overnight hours. Wind gusts above 60 mph were common along the squall line, and a station near Red Rock, OK, reported a 99-mph gust at 1:55 am CST.

Figure 2. All tornadoes (F/EF0 - F/EF5) reported in the era of reliable records, from 1950 to 2014, during the months of November through February. Initial tornado reports from November 16, 2015, across Texas, Oklahoma, Kansas, and Nebraska are shown in white triangles. Image credit: Ian Livingston and, used with permission.

An unprecedented High Plains outbreak for November
Dynamic upper-level storms like the one on Monday often pull moisture up into the Central Plains and Mississippi Valley, which is why places like Iowa can occasionally see tornadoes even in November. Mid-autumn tornado outbreaks are much more likely across the Deep South, where rich low-level moisture is more readily available. Some of the deadliest and most destructive tornadoes in Southern history have struck in November.

In contrast, big upper-level storms seldom allow warm, moist low-level air to be swept northwest into the Texas and Oklahoma Panhandles and western Kansas this late in the autumn. For one thing, the elevation of Monday’s tornado-struck areas is around 2500 to 3000 feet, which reduces the potential depth of available moisture for severe thunderstorms. Monday’s upper low had a pronounced north-south orientation early in the day, which allowed the deep moisture to be pulled further northwest than usual. Often in such cases, the upper low is “cutting off,” or becoming detached from the jet stream, which would tend to reduce the amount of wind shear. In this case, however, there was plenty of jet-stream energy behind the low, which forced it eastward late Monday and quickly boosted the amount of vertical wind shear. The dynamics strengthened so dramatically that nearly all of the tornadoes occurred near dusk or after dark, without any help from daytime heating to add instability to the atmosphere.

Figure 2. When ENSO is in a warm, or El Niño, phase (top), the frequency of springtime tornadoes goes down. When it is in a cool, or La Niña phase (bottom), tornadoes increase (indicated by red areas). The effect is strongest in the boxed area. Image credit: IRI from Allen et al., Nature Geoscience, 2015.

Did El Niño or climate change have anything to do with this?
Strong El Niño events are associated with cold-season tornadoes along the Gulf Coast, and especially in Florida. There is no established link between El Niño and fall/winter tornadoes in the Great Plains. In fact, El Niño tends to reduce the likelihood of springtime tornadoes across the Southern Plains, as we discussed in an April blog post (see Figure 2). It’s possible that the ongoing strong El Niño event is playing a role in the jet-stream configuration, or the availability of deep moisture, but if so, this is more a function of the particulars of this autumn rather than a well-established fingerprint of El Niño.

Likewise, any direct role of climate change in this event would take time and research to establish, ideally through attribution research. “I don't know how to put this event in the context of lengthening tornado seasons or climate. It's such an outlier,” said Harold Brooks (National Severe Storms Laboratory), who is one of the world’s foremost experts on tornado climatology and the influence of climate change on tornadoes. Brooks added: “Even in the absence of climate change, you can have extreme outliers,” such as the 32 tornadoes that struck on January 24, 1967, from Oklahoma to Wisconsin.

More severe weather, heavy rain possible Tuesday in Mississippi Valley
The exceptionally moist air mass fueling Monday’s storms has been shunted east into Arkansas and Louisiana, raising the potential there for severe weather and flash flooding on Monday afternoon and evening. The 00Z Tuesday radiosonde profile from Oklahoma City showed near-record amounts of moisture for November (3.71 cm or 1.46”), and at 12Z Tuesday, the sounding from Lake Charles, Louisiana, contained 4.91 cm (1.93”) of available moisture, also near the top end of moisture content observed in November. SPC’s convective outlook issued at 10:30 am CDT Tuesday has an enhanced risk of severe weather across eastern AR and LA, which is at risk for high winds and heavy rain from the advancing front and squall line as well as tornadoes from any supercell storms that form ahead of or within the line. Heavy rains and potential flash floods are another threat for Tuesday, with bursts of 3-5” of rain possible. NOAA’s Weather Prediction Center has a moderate risk of rainfall exceeding flash-flood guidance criteria, centered on northeast Arkansas and southeast Missouri, as a low-level jet stream blowing at up to 90 mph will be importing ample quantities of Gulf moisture.

Figure 4. Enhanced infrared image of Invest 90E in the Eastern Pacific as of 1730Z (12:30 pm EDT) Tuesday, November 17, 2015. Image credit: NOAA/NESDIS.

Invest 90E in the Eastern Pacific likely to become a very late-season tropical storm
Satellite images show that an area of disturbed weather (Invest 90E) in the Eastern Pacific several hundred miles southwest of Mexico’s Baja Peninsula has acquired some spin and a respectable amount of heavy thunderstorm activity. The 7 am EST Tuesday run of the SHIPS model showed ocean temperatures were a  near record-warm 30°C (86°F) and wind shear was a low 5 - 10 knots, conditions that favor continued development. The 00Z Tuesday runs of both the GFS and European models showed 90E becoming a tropical depression by Thursday. In their 1 pm EST Tuesday Tropical Weather Outlook, NHC gave 2-day and 5-day odds of development of 40% and 70%, respectively. If 90E does become Tropical Storm Rick, it would be one of the latest-forming tropical storms in the history of the Eastern Pacific. Since accurate records began in 1949 (with higher-quality satellite records beginning in 1971), the Eastern Pacific has seen only four tropical storms form after November 18: December 5, 1983 (Winnie), November 27, 1971 (Sharon), November 27, 1951 (Unnamed), and November 20, 2011 (Kenneth.) None of these storms hit land. 90E will wander slowly to the west-northwest or northwest at speeds less than 5 mph through Thursday. A turn to the northeast towards Mexico’s Baja Peninsula is possible early next week, but the models are showing a variety of long-range solutions for the path of 90E, and it remains uncertain if this storm will pose a threat to Mexico or not.

Tropical Storm In-fa a threat to Guam
In the Western Pacific, Tropical Storm In-fa formed on Tuesday morning in the waters about 1200 miles east-southeast of Guam. In-fa is expected to track west-northwest and intensify into a typhoon later this week, and could put pass very close to Guam on Saturday. There is the potential that In-fa could rapidly intensify into a major Category 3 storm before reaching Guam.

The Atlantic is quiet with no tropical cyclone formation expected for the next five days.

Bob Henson (severe weather), Jeff Masters (tropical)

Tornado Hurricane

El Niño of 2015 Hits All-Time Record Strength for a 1-Week Period

By: JeffMasters, 4:44 PM GMT on November 16, 2015

Incredibly warm waters continue to build across the equatorial Pacific, and the El Niño event of 2015 has just set a record for the warmest waters ever observed in the equatorial Pacific over a 1-week period. Sea-surface temperatures (SSTs) in the Pacific’s Niño3.4 region, between 90°W and 160°E longitude and 5° north/south latitude, are considered the benchmark for rating the strength of an El Niño event. The weekly departure of SST from average in this region hit +3.0°C (5.4°F) over the past week, NOAA announced in their November 16 El Niño update. This exceeds the previous 1-week record warmth in the equatorial Pacific of 2.8°C above average set during the week of November 26, 1997; accurate El Niño records extend back to 1950. However, the standard measure for the strength of an El Niño event is the three-month average Niño 3.4 SSTs, and the El Niño of 2015 is not yet officially considered the strongest on record. The August-September-October 2015 three-month average Niño 3.4 SSTs were 1.7°C above average, good for only the 2nd warmest on record, behind 1997. Judging from the trajectory of SST anomalies in Figure 1, though, it is likely that one of the late-year three-month average Niño 3.4 SST values in 2015 will end up upending 1997's record warmth and claim for the 2015 the title as strongest El Niño event on record. El Niño can't get much stronger than it is now, though, since there simply isn't enough warm water available in the Western Pacific to transport to the Eastern Pacific; wunderblogger Steve Gregory speculated in his Friday post that El Niño may now be peaking, and will begin a slow decline over the the next three months. Even so, El Niño will decline only gradually, and we can expect significant global impacts on weather during the coming winter. Below, I'll dive into some of the major non-U.S. impacts we can expect (and have already seen) from a strong El Niño; Bob Henson has covered the likely U.S. impacts in a number of previous posts, which are linked at the bottom of the blog.

Figure 1. Sea-surface temperatures (SSTs) in the Pacific’s Niño3.4 region, between 90°W and 160°E longitude and 5° north/south latitude, are considered the benchmark for rating the strength of an El Niño event. The weekly departure of SST from average in this region hit +3.0°C (5.4°F) over the past week, beating the previous record of +2.8°C set during November 1997 during that year's super-El Niño. Image credit: Jan Null Golden Gate Weather, via Twitter.

Figure 2. The typical shifts from normal climatic condition during the Northern Hemisphere winter (December - February) during El Niño episode. Image credit: NOAA/Climate Prediction Center.

An intense hurricane/typhoon season in the Pacific, and quiet in the Atlantic
The unusually warm waters that El Niño brings to the North Pacific usually leads to well above-average hurricane and typhoon activity in that ocean basin, with unusually intense storms. The strongest Eastern Pacific hurricane ever recorded prior to 2015, Category 5 Hurricane Linda, occurred during the strong El Niño year of 1997. Linda had sustained winds up to 185 mph and a central pressure of 902 mb on September 12th. The El Niño year of 1997 also saw a record number of Category 5 storms in the Northwest Pacific—ten, and a record ACE index of 594. At one point on October 17, 1997, Super Typhoon Joan had top sustained winds of 185 mph, while Super Typhoon Ivan had top winds of 180 mph--the first time that Category 5 storms of such extreme intensity existed simultaneously. Typhoons tend to form farther to the east in an El Niño episode, due to the warmer waters over the Central Pacific. Thus, El Niño-year typhoons take longer tracks over water before hitting Asia, resulting in a greater chance of reaching Category 5 intensity.

True to expectations, the strong El Niño event of 2015 has led to record-smashing activity for hurricanes and typhoons in the North Pacific. The all-time most intense Eastern Pacific hurricane on record is now 2015’s Hurricane Patricia, which attained a remarkable 879 mb pressure with sustained winds of 200 mph. It's also been a record-active Central Pacific hurricane season in 2015, and a much more active than usual Western Pacific typhoon season. The Accumulated Cyclone Energy (ACE) for the Western Pacific was 161% of average as of November 13, and was 200% of average for the combined Eastern and Central Pacific Oceans. However, it’s a different story in the Atlantic, where El Niño has brought dry air and strong upper level westerly winds, creating high wind shear, suppressing Atlantic hurricanes. The ACE in the Atlantic this year has been only 57% of average.

Figure 3. Category 5 Hurricane Linda, the strongest hurricane on record in the Eastern Pacific prior to 2015,  had sustained winds of 185 mph and a central pressure of 902 mb on September 12, 1997.

Flooding in South America
El Niño refers to the (Christ) Child in the Spanish language, and got its name from Peruvian sailors, who noted the arrival of warm waters off the coast of Peru typically coincided with Christmas. And it is in Peru and surrounding countries where the impact of El Niño on the weather can be the most severe. The unusually warm waters commonly cause record-breaking rains along the Pacific coast of equatorial South America, since warm air holds much more water vapor.

The two deadliest floods in Ecuador's history occurred during strong El Niño events: in November 1982 (307 killed) and during October 1997 (218 killed.) Peru’s deadliest flood (518 killed) also occurred during the 1997 El Niño. As reported by AP, a United Nations-backed study said that the 1997 - 1998 El Niño cost Bolivia, Colombia, Ecuador, Peru and Venezuela nearly $11 billion.

Peru declared a pre-emptive state of emergency in July 2015 for 14 of its 25 states, appropriating about $70 million to prepare for the coming fall and winter rains. Authorities are clearing river beds of debris, reinforcing river banks with rocks and sandbags, and fortifying reservoir walls.

Figure 4. Residents of of Naranjal, Ecuador, walk along one of the town's flooded streets on November 28, 1997, after El Niño-driven floods killed at least 41 people along Ecuador's coast. Photo credit: ALICIA SMITH/AFP/Getty Images.

El Niño and drought
The warm waters off the Pacific coast of Peru during a strong El Niño episode generate a column of rising air over the tropical Eastern Pacific. Once this rising air reaches the bottom of the stratosphere, which acts as a stable lid preventing further rising motion, the warm air is forced to spread out to the east and west along the Equator. This air eventually sinks over tropical regions well to the east and the west of the Eastern Pacific to complete a huge circulation cell several thousand miles in diameter. Since sinking air warms and dries as it descends, areas of high pressure and drought tend to form in these sinking air regions. To the west of the Eastern Pacific, El Niño events tend to create drought over Indonesia, New Guinea, and Northern Australia; to the east, drought commonly occurs over Central America, Northern Brazil and the Caribbean.

Figure 5. Greenhouse gas emissions from Indonesian forest fires have exceeded all emissions from the U.S. economy on most days in September and October 2015. Image credit: World Resources Institute.

Drought in Indonesia
As discussed in detail in the Jeff Masters October 13 post, Costliest (and Deadliest?) Disaster of 2015: Indonesia's $14 Billion Fires, the El Niño events of 2015 and 1997 - 1998 brought devastating drought and fires to Indonesia and neighboring countries. This year's fires in Indonesia are on track to be their most expensive disaster in history, beating the $9.3 billion price tag of the 1997 - 1998 fires.

Drought in Australia
Drought in parts of southern and northern Australia typical for El Niño has already begun in 2015, and may cut as much as 1 percent off of the country's GDP, said Andrew Watkins, supervisor of climate prediction services at the Australian Bureau of Meteorology, in an AP interview. October 2015 was Australia’s hottest month ever recorded, and rainfall was below average over most of the country. Two of the three most expensive droughts in Australia’s history occurred during the moderate El Niño years of 2002 and 1992.

Drought in Central America, the Caribbean and Brazil
The atmospheric circulation associated with El Niño brings dry air and high pressure to northern Brazil, the Caribbean, Central America and the tropical Atlantic; these conditions tend to bring drought. According to the U.N.’s Food and Agriculture Organization, dry weather caused by El Niño through September 2015 was responsible for declines of 60 percent in maize and 80 percent in beans across the Central American countries of El Salvador, Guatemala, Honduras and Nicaragua (thanks go to Natasha Geiling of Climate Progress for this link.) Severe drought is also impacting eastern Puerto Rico, according to the latest U.S. Drought Monitor report. As of November 12, San Juan was 13” below their average precipitation of 47” for the year-to-date period. Water rationing was imposed for several hundred thousand residents over the summer, but was eased in mid-September. On St. Barthelemy in the Lesser Antilles Islands, rainfall from January - September 2015 was only 8.65"--way short of their usual 23.74" (thanks go to wunderground member zicoille for this link.) The latest Global Drought Monitor shows areas of drought were also occurring over Northern Brazil this year, though this drought was not widespread. Only one of the top five most expensive droughts in Brazil’s history (2014, 1978, 2004, 2012, and 1985) occurred during an El Niño year—2004, during a weak El Niño.

Failure of the monsoon in India
The atmospheric circulation patterns brought on by an El Niño event usually cause much reduced monsoon rains in India. According to EM-DAT, the International Disaster Database, more than 4.2 million people died in India between 1900 - 2014 due to droughts from failed monsoon rains, primarily during El Niño years. Up until the late 1960s, it was common for the failure of the monsoon rains to kill millions of people in India; the 3-year drought that began during the strong El Niño event of 1965 killed at least 1.5 million people. However, since the Green Revolution of the late 1960s--a government initiative to improve food self-sufficiency using new technology and high-yield grains--failure of the monsoon rains has not led to mass famine in India.

As of  October 1, 2015, this year's monsoon had brought rains 14% below normal to India, in line with pre-season predictions of a deficient monsoon. This would not rank as one of the top five worst Indian monsoons for rainfall deficit, though. Here are the top five worst years for rainfall deficit in India, which all occurred during El Niño conditions:

1) 1877, -33% (strong El Niño)
2) 1899, -29% (weak El Niño)
3) 1918, -25% (weak El Niño)
4) 1972, -24% (strong El Niño)
5) 2009, -22% (weak El Niño)

Drought in Africa
El Niño typically bring deficient rains across Southern Africa during their rainy season, which normally starts in October and lasts through March. According to an October 1 report from Oxfam, during the 2014 - 2015 rainy season, the rains came more than a month late, then became extraordinarily heavy in mid-December through January, causing extensive flooding and crop damage. The combination of drought and flooding in early 2015 have caused Malawi, Zimbabwe, and Mozambique to have major food security issues heading into the coming El Niño rainy season.

Figure 6. Monthly precipitation departure from the long-term average during October 2015. Map by, data from the CPC ARC2. Image credit: NOAA El Niño blog.

North America: cool and wet in the south, warm in the north
Bob Henson's July 2015 post, What to Expect from El Niño: North America, discussed in great detail the usual impacts El Niño has on the winter weather in North America. These include potential drought-easing rains for California; milder and drier weather in the Pacific Northwest, Northern Plains, and western Canada; below-average snowfall in the Northern Rockies and above average in the Southern Rockies; and rainy and cool across the Gulf Coast. The impacts on the Northeast U.S. are more complicated, as he discussed in his follow-up post, What to Expect from El Niño: How Much Snow Back East? His post from last Friday, Will El Niño Bring a December Warm Wave to North America? has the latest on what to expect in North America from El Niño.

See our new El Niño micro-site for full details on the current status and forecast for El Niño.

Video 1. Chris Farley of Saturday Night Live explains everything you need to know about El Niño.

Our next post will be Wednesday at the latest.

Jeff Masters

El Niño

Will El Niño Bring a December Warm Wave to North America?

By: Bob Henson , 5:43 PM GMT on November 13, 2015

If you’re looking for an old-fashioned holiday, you may be out of luck across large parts of the U.S. and Canada, at least when it comes to December cold. El Niño climatology and seasonal forecast models are pointing toward high odds of a very mild December across most of the continent east of the Rockies and north of the Deep South. We wouldn’t expect every day to be unusually balmy--and in December, “warmer than average” can still be quite chilly--but the analogue years and the model forecasts do raise the possibility of at least a few days of record-melting weather across a vast area.

How the effects of a strong El Niño unfold during autumn
WU contributor Eric Webb (@webberweather) tweeted a powerful image the other day (Figure 1 below). It’s a composite showing the likelihood of above- and-below-average temperatures for each month during strong El Niño events (11 in all since 1895). Notice how the composites change dramatically from October to November to December, before settling into the prototypical mild-north/cool-south pattern for January through March.

Figure 1. Month-to-month variations in average temperature during strong and “super” El Niño events between 1895 and 2014. Temperature departures are shown in blue/green colors (cooler than average) and red/orange colors (warmer than average), as calculated against the long-term average for the period 1895-2000. The El Niño events in these composites (peak Niño3.4 indices of at least 1.5°C above average for at least three overlapping three-month periods) include 1896-97, 1902-03, 1930-31, 1940-41, 1957-58, 1965-66, 1972-73, 1982-83, 1987-88, 1991-92, and 1997-98. Image credit: Eric Webb, @webberweather, using a mapping/analysis tool from NOAA’s Earth System Research Laboratory.

Figure 2. Departures from average in U.S. temperatures for October 2015. Image credit: NOAA National Centers for Environmental Information.

Thus far, the 2015-16 El Niño is behaving much as you would expect a strong event to behave in terms of U.S. temperature effects, with a spoonful of long-term warming and a few sprigs of natural variability mixed in. Figure 2 shows that we saw a warmer-than-average western and central U.S. during October 2015--in fact, record-warm in some areas--with mostly near-average temperatures near the Ohio Valley and along most of the East Coast. This roughly matches the west-to-east contrast depicted in Figure 1 for October, provided you bump up the temperatures from Figure 1 across the board. For the first few days of November 2015, we’re again in the groove for the overall pattern one would expect based on the composites in Figure 1: cooler-than-average readings in the far West and mild readings in the East. The biggest departure from the El Niño composite so far this month is the marked mildness over the Midwest. We still have more than two more weeks of November to go, but NOAA’s latest 6-to-10 day and 8-14 day outlooks strongly support the cool-West/mild-East pattern that fits with the Figure 1 climatology.

What do seasonal climate models say?
NOAA’s Climate Forecast System model (CFSv2) has been singing a consistent tune over the last few days, and it doesn’t sound like your typical holiday song. For more than a week, daily runs of the CFSv2 have called for an unusually mild December across nearly all of North America, with the possible exception of Texas, Mexico, and Alaska. “With such persistence in the CFS, I don't see much room for deviation from this forecast,” says WSI’s Michael Ventrice, who adds that the ECMWF seasonal model paints a similar picture. Overall, says Ventrice, this is “some of the most anomalous warmth I've ever seen” in monthly model output.

Figure 3. Surface temperature forecasts for December from NOAA’s CFSv2 model, produced each day from November 4 (top left) to November 12 (bottom right). Temperatures are shown as departures from the monthly average in degrees Celsius, with reds and tans indicating warmer-than-normal readings for the month.

The caveats
Every El Niño event is different, and we only have two “super” El Niños in modern records that compare to the current event in strength (1982-83 and 1997-98). Even across the 11 cases encompassed in the Figure 1 composites, not every December shows the breadth of unusual mildness implied in the composites. In each of these 11 cases, the warmth shows its own distinctive fingerprint. However, very few parts of the country experienced below-average monthly readings during any of these Decembers. The exceptions are 1896 and 1902, which run cool mainly because they fall toward the cool end of the 1895-2000 comparison period, and the odd case of December 1972, which came in below average for most of the contiguous U.S. west of the Appalachians.

At NOAA’s Climate Prediction Center, forecaster Stephen Baxter provides some more perspective. Although the warm-West/less-warm-East pattern shown in Figure 2 does appear to roughly match the El Niño composite in Figure 1, October 2015 was clearly a lot warmer than the composite. Baxter points out that, by itself, the El Niño/Southern Oscillation (ENSO) doesn’t tend to produce the type of dramatic nationwide warmth seen in both September and October. Thus, he said, “To a first order, ENSO is not to blame for the warm autumn thus far." Baxter added that the CFSv2 isn’t extremely skillful predicting monthly temperatures this far out, because of the role of month-to-month climate variability. NOAA will issue its next set of long-lead climate outlooks on November 19. “We will likely have lots of red on our December outlook," said Baxter, "but with more modest probabilities than those inferred from the CFSv2. So while the odds of a record or near-record warm month are substantially elevated across parts of the northern contiguous U.S., it is still not the most likely outcome.”

The dramatic month-by-month evolution seen in Figure 1 for autumn settles down by January. At that point, the Pacific jet stream is much more likely to fall into the midwinter pattern typical of strong El Niños, with storm systems barreling into California and across the South while mild air spreads across much of the northern U.S. and eastern Canada. These atmospheric effects can persist through much of winter even if the warm sea-surface temperatures associated with El Niño begin to cool. One potential fly in the ointment is the possibility of a negative North Atlantic Oscillation, which is highlighted in the latest Arctic Oscillation outlook produced by Judah Cohen and colleagues at Atmospheric and Environmental Research. Snow cover advanced more quickly than usual over Siberia during October, and Cohen’s work has related this variable to an enhanced risk of negative NAO conditions by early winter, especially in January and February. Running counter to the warming effect of a strong El Niño, a period of negative NAO would favor intrusions of cold air over the northeast U.S. In the past, the combination of a negative NAO and a strong El Niño has led to some noteworthy winter storms along and near the East Coast, so it will be interesting to see if this pairing actually develops.

What about the ski season?
Milder-than-usual winter weather is anathema to skiers and snowboarders, but snow hounds now have a place to find winter outlooks specific to their favorite resorts. The website unveiled its first-ever nationwide winter snow outlooks in October (see map below), with the forecasts just updated this past Tuesday. To the best knowledge of company founder Joel Gratz, this is the first long-range seasonal snow forecast specifically tailored for ski areas. The outlooks were produced in collaboration with Amato Evan, an assistant professor at Scripps Institution of Oceanography. Evan’s technique includes the precipitation and temperature outlooks common to most seasonal forecasting efforts, but it goes a step further by translating these two variables into the likelihood of snowfall at various locations and time periods. The technique also incorporates the tendency of El Niño years to skew snowfall toward the southern half of the western U.S. ski areas, as evident in Figure 4.
Gratz adds a cautionary/encouraging note: “If we are forecasting that a ski area will see below average snowfall over a 6-month season, they will still likely experience plenty of snow storms and powder days, so don’t be too picky.”

Have a great weekend, everyone!

Bob Henson

El Niño

After Iowa Tornadoes, Threat of Severe Lakeshore Flooding in Michigan

By: Bob Henson , 4:42 PM GMT on November 12, 2015

The intense midlatitude storm that swept across the Great Plains on Wednesday, dropping several tornadoes across central Iowa, may produce the worst flooding in decades along the southeast shores of Lake Michigan on Thursday. The powerful surface low at the heart of the storm is being energized by a pocket of extremely strong winds at upper levels. The radiosonde launched at 6:00 pm EDT Wednesday night from the Springfield, Missouri, office of the National Weather Service sampled west-southwest winds raging at 155 knots (178 mph) near the 300-mb level, or about 30,000 feet above ground level. See the YouTube clip at bottom for a taste of what it was like to launch this radiosonde in surface winds gusting to 40-50 mph.

Figure 1. WunderMap composite radar display from 0412Z Thursday, November 12, 2015 (10:12 pm CST Wednesday), as the line of thunderstorms that swept across Iowa earlier in the day reached the Chicago area. Other scattered storms extend along the front all the way to Texas.

Many towns and cities across the Midwest experienced tree damage and scattered power outages on Wednesday due to widespread high winds. As a narrow ribbon of unstable air flowed north ahead of the surface low and associated front, a crop of small supercells emerged across south central Iowa, leading to a mini-outbreak of tornadoes between about 2:00 and 5:00 pm on Wednesday afternoon. A total of 10 tornado reports were received by the NWS Storm Prediction Center (SPC). No major destruction was reported, but a few homes and industrial buildings suffered serious damage. This story provides a detailed roundup of the tornado and multi-state high-wind damage from Wednesday and early Thursday. As noted by the Weather Channel’s Stu Ostro, the coverage of high wind reports across Iowa, Missouri, and Illinois qualifies the event as a serial derecho, one of two main types of derechoes.

Perhaps the closest call of the day on Wednesday was a tornado that developed near the Des Moines International Airport around 4:30 pm. The twister was visible to staff at the nearby NWS office, as noted on a special observation that you’ll find in the hourly weather history section of the WU daily almanac.

Mid-autumn tornadoes in Iowa are rare but not unprecedented: the state’s largest November outbreak on record produced 12 tornadoes on November 12, 2005, including an F3 twister that killed one person and injured several others. Another of that day’s tornadoes, an F2 on the outskirts of Ames, forced the evacuation of fans streaming into the Iowa State University stadium for an football game. (The ISU mascot is, of course, the Cyclones).

Figure 2. Damage from Wednesday's storms to a home south of Melrose in Monroe County, Iowa. Image credit: Norm Vote/KCCI, via NWS/Des Moines.

High winds, high lake levels team up for flood risk
Strong winds were spreading across the Great Lakes region on Thursday, already gusting to 55 mph in parts of southwest Michigan. The winds are paving the way for an unusually strong episode of coastal flooding along the east shore of Lake Michigan. The storm has prompted the first lakeshore flood warning from the NWS Grand Rapids office since the 1990s. On top of an expected 6-to-12-inch storm surge, waves could peak as high as 16 feet, with the largest waves expected in the Holland/Saugatuck area of southwest Michigan. Beach and dune erosion may be “severe,” warns the NWS. Further east, the high winds are expected to produce a "seiche" that pushes up water levels up on the east end of Lake Erie by several feet; see Lee Grenci's WU blog post for details

Thursday’s storm is indeed a strong one--high wind warnings are in effect from southern Michigan and northern Indiana all the way to western New York, for gusts as high as 60 mph--but there is another factor at work. This year, Lake Michigan and the other Great Lakes are seeing water levels significantly above the long-term average for the first time in the 21st century. After hitting a record-low level in January 2013, the height of Lakes Michigan and Huron (considered a single unit by the U.S. Army Corps of Engineers) has risen more than three feet. The reason: Relatively wet, cool conditions have predominated over the region during the last two years, sending more streamflow into the lakes as well as cutting down on the loss of lakewater through evaporation. Extensive ice cover during the winter of 2013-14 also helped cut back on evaporation rates. In contrast, between 1999 and 2013, the balance was tilted toward warmer air and water temperatures, less ice cover, and greater evaporation. The lakes are prone to large multidecadal variations in water height.

Along with these factors, the amount of water drawn from the Great Lakes for industry, agriculture, and consumer use is now on the decline, thanks in large part to the Great Lakes Compact, a U.S.-Canada agreement that went into effect in 2008. Withdrawal of Great Lakes water by the United States has been dropping by about 4 percent a year since 2007.

The NOAA Great Lakes Environmental Research Laboratory is hosting a press conference on November 19 exploring the potential impacts of El Niño on Great Lakes water levels. Slides will be posted on the GLERL website after the event.

The howling winds across the Great Lakes on Thursday and Friday will also lead to some lake-effect precipitation, with rain and snow showers in New York and up to 7” of snow across parts of the Upper Peninsula of Michigan. In his latest post, WU blogger Steve Gregory weighs in on the recurrently storm pattern expected to persist over the contiguous U.S. for the next week or two. NOAA/SPC is already highlighting the possibility of severe weather, including tornadoes, from Texas into Louisiana next Monday and Tuesday.

Bob Henson

Figure 3. Observed (blue dots) and projected (red rectangles) surface water elevation for Lakes Michigan and Huron from 1996 to 2016. Image credit: NOAA Great Lakes Environmental Research Laboratory.

Winter Weather Tornado Severe Weather Flood

Hurricane Kate Races Across Atlantic; Severe Weather Threatens Midwest

By: Bob Henson , 5:10 PM GMT on November 11, 2015

Even as it gets shunted quickly offstage, Hurricane Kate is putting on a respectable closing act in the central Atlantic. On Wednesday morning, Kate became the fourth hurricane of the 2015 Atlantic season. Its top sustained winds remained at minimal hurricane strength, 75 mph, in the 10 am EST advisory from the National Hurricane Center. At that point, Kate was located about 500 miles northeast of Bermuda, with its center of circulation pushing east-northeast at 45 mph. Kate’s hurricane-force winds are limited to within 35 miles of its center, but tropical-storm-force winds have expanded to a radius of up to 205 miles. Sea-surface temperatures along Kate’s path are marginal for sustaining a hurricane--only about 25°C, or 77°F. However, these readings are about 2°C above average, close to record-warm values for the region and season. According to NHC’s Eric Blake, Kate is the latest hurricane on record to develop in the Northwest Atlantic north of 35°N and west of 65°W. Two previous Hurricane Kates, one in November 1985 and one in September/October 2003, each intensified to Category 3 strength.

Figure 1. GOES-East image of the North Atlantic at 1515Z (10:15 am EST) Wednesday, November 11, 2015. Labeled are Hurricane Kate (center) and Abigail (right), the first named storm in a winter-storm naming system being tested this year by the UK Met Office and Met Éireann (see below). Image credit: NOAA-NASA GOES Project.

Kate’s remnants to succeed the UK’s first named winter storm, Abigail
Strong jet-stream winds are moving Kate into the central Atlantic, with a large nontropical center of low pressure located just west of Kate (see Figure 1). As Kate loses its tropical identity over the next 24 to 48 hours, the two cyclones will merge and continue racing east-northeast, ahead of a strengthening upper-level trough in the Northwest Atlantic. The combined system could bring strong winds and heavy rain to the British Isles late this weekend.

Kate’s remnants will arrive on the heels of Abigail, the first winter storm ever to be officially named by the UK Met Office and Met Éireann. The naming system is a joint pilot project of the Met Office and Ireland’s meteorological agency. This year’s names were chosen from thousands of nominations submitted via email, Facebook, Twitter. “Over the past few winters the naming of wind storms that affected Ireland and the United Kingdom (such as the 'St Jude's day storm') has shown the benefits of establishing a protocol for the naming of mid-latitude storms,” the Met Office said in a statement on September 8. In line with the NHC’s naming practice for tropical systems in the North Atlantic, the Met Office will not use names starting with the letters Q, U, X, Y and Z. Abigail is expected to bring wind gusts as high as 90 mph to far northern Scotland.

Record-warm November low for the UK
According to the UK Met Office, the United Kingdom saw the warmest November night in its recorded weather history on Tuesday, with the Northern Ireland town of Murlough scoring a overnight low on November 10 of 16.1°C (61.0°F). Murlough reached a high on Tuesday of 18.5°C (65.3°F), the day’s warmest reading in the British Isles. I have not yet been able to verify whether or not Murlough’s temperature dipped below 16.1°C before midnight Tuesday night.

The Tuesday warmth is part of a record-smashing “warm wave” bringing much of western Europe some of the mildest November temperatures ever recorded there. WU weather historian Chris Burt has more on this event, as well as the record November warmth over parts of the eastern U.S., in his latest post, published on Tuesday.

Figure 2. Convective outlook issued by the NOAA Storm Prediction Center on Wednesday morning, November 11, 2015.

Severe weather threat across parts of the Midwest
A potent autumn storm system plowing across the Great Plains is on track to trigger thunderstorms, some possibly severe, across the Missouri and Mississippi valleys on Wednesday. The greatest threat (enhanced) is across southeast Iowa, northeast Missouri, and western Illinois, just ahead of the surface low, but severe storms could also erupt along the cold front that extends south toward Texas from the surface low. Moisture scoured out of the Gulf of Mexico by the last cold front has had some trouble returning northward, which is tamping down this system’s potential for severe weather. Even so, NOAA’s Storm Prediction Center expects a cluster of supercells to emerge in the enhanced risk area, potentially congealing into a line of storms later this evening. Tornadoes are possible during the initial supercellular phase, with the risk of damaging straight-line winds increasing as the storms push into Illinois. We will be covering today’s severe weather as it unfolds in a WU live blog.

Bob Henson

Hurricane Severe Weather Extreme Weather

Kate Strengthens in Atlantic; Megh Dissipates in Yemen

By: Bob Henson and Jeff Masters , 4:52 PM GMT on November 10, 2015

Tropical Storm Kate is nearing hurricane status well east of Florida and Georgia as it begins sweeping into the open Atlantic. As of 10:00 am EST Tuesday, the National Hurricane Center pegged Kate’s top sustained winds at 60 knots (70 mph), based on peak surface winds of 61 kt from Hurricane Hunter data collected via the SFMR radiometer. Kate is a compact storm, with tropical storm force winds extending only 80 miles from its center, but its structure is considerably better than on Monday, with a symmetric core of strong convection (showers and thunderstorms) and some banding on its east side. The effects of increasing southwesterly wind shear (15 – 20 knots) are becoming evident, as Kate takes on the comma shape common to tropical cyclones undergoing subtropical/extratropical transition.

Figure 1. Latest satellite image of Tropical Storm Kate.

Even as Kate moves northeast at an increasingly rapid clip--more than 20 mph--the storm is passing over waters that are near record-warm levels for the time of year, at 1°C to 2°C above the seasonal average. Later on Tuesday, Kate’s track will take the storm over waters cooler than the threshold for tropical development of 26°C (79°F), hastening its extratropical transition. Phase space diagrams from Robert Hart and Jenni Evans (Florida State University) show Kate morphing into an asymmetric warm-core cyclone over the next couple of days. At the same time, Kate’s peak winds should continue to increase and expand, powered by the strong upper-level jet stream that will soon envelop the storm. Kate is likely to become a hurricane later on Tuesday or early Wednesday before going post-tropical by later in the week.

Kate is the Atlantic’s most intense tropical cyclone on record for November during the five years since 1950 with strong El Niño conditions present in October-December: 2015, 1997, 1982, 1972, and 1965. Only one other named system was observed during those Novembers: 1972’s Subtropical Storm Delta. See our Monday post for more on Kate’s significance as the 11th named system of the year.

Other Kates in Atlantic hurricane history
Kate shares the name of 1985’s Hurricane Kate, which produced the latest US landfall of any hurricane on record. Kate brushed by Key West and moved into the eastern Gulf, where it peaked as a major hurricane, with top sustained winds of 120 mph. On the afternoon of November 21, Kate made landfall near Mexico Beach, FL, bearing sustained winds of 100 mph. Kate was a destructive storm, causing an estimated 15 fatalities and $700 million of damage in 1985 US dollars. Another Hurricane Kate also became a Category 3, this time in early October 2003, but it spun harmlessly over the central Atlantic, finally taking a swipe at Newfoundland near the end of its life.

Tropical Cyclone Megh makes a second landfall in Yemen and dissipates
Tropical Cyclone Megh penetrated deep into the Arabian Sea's narrow Gulf of Aden to make an improbable landfall in western Yemen near Aden at approximately 6 pm EDT Monday evening. At landfall, Megh was a rapidly weakening tropical storm with top winds of 40 mph. Megh rapidly dissipated after landfall, spreading only a few heavy rain showers over western Yemen. Satellite data suggests that Megh dumped very little rain over western Yemen, and only minor flooding and damage likely resulted. That's not the case on Yemen's Socotra Island, where Megh made a direct hit as a major Category 3 storm with 125 mph winds on Sunday, bringing a second round of devastation to an island hard-hit the previous week by the passage of Tropical Cyclone Chapala.

According to Dr. Phil Klotzbach, Magh has pushed the Accumulated Cyclone Energy (ACE) in the North Indian Ocean in 2015 to 39.3 ACE units. Since 1990, only 1999 (44 ACE) and 2007 (46 ACE) have had more. An average season has just 18 ACE units.

Figure 2. MODIS image of Tropical Cyclone Megh over western Yemen at 07:25 UTC November 10, 2015. Megh made landfall near Aden, Yemen about 7 hours previous to this image, with top winds near 40 mph. Image credit: NASA.

Forty years ago today: the wreck of the Edmund Fitzgerald
The “gales of November” immortalized in a hit record struck 40 years ago this week, on November 10, 1975, when a fierce midlatitude storm hammered Lake Superior and sank the US freighter SS Edmund Fitzgerald, killing all 29 crew members. Fans of the Canadian balladeer Gordon Lightfoot already know many particulars of the story, although “The Wreck of the Edmund Fitzgerald”--which hit #2 on the U.S. Billboard chart in 1976--was not a precisely accurate retelling of the disaster. The ship was heading east across Lake Superior with a load of iron ore pellets when the unexpectedly intense storm struck early on the 10th, packing northeast winds of 52 knots (60 mph). As the Edmund Fitzgerald headed toward the east end of Lake Superior through the day, the surface low passed close by, throwing the ship into a “hurricane westwind,” as Lightfoot put it. By late afternoon, the ship’s systems were failing, and the last transmission from the Fitzgerald reached a nearby ship at 7:10 pm. The ship’s wreckage was found over the next several days, although none of the victims were ever recovered.

Figure 3. A 1971 photo of the SS Edmund Fitzgerald. It remains the largest ship known to have sunk in the Great Lakes. Image credit: Greemars/Wikimedia Commons.

A CIMSS Satellite Blog post on Tuesday included satellite imagery from 1975 depicting the storm that sank the Edmund Fitzgerald. WU weather historian Christopher Burt included this storm in a roundup of Upper Midwest weather events that all happened on November 10. In a fascinating Weatherwise article, Steve Ackerman and John Knox related the Edmund Fitgerald storm’s particulars in the context of Gordon Lightfoot’s lyrics. The website Songfacts has a variety of interesting tidbits about the song itself. Apparently Lightfoot was motivated to write “The Wreck of the Edmund Fitzgerald” in part because the ship’s name was repeatedly misspelled in a magazine article.

Wunderblogger Steve Gregory has a new Monday afternoon post, Stronger Storm Systems and Wild Model Forecasts.

Bob Henson and Jeff Masters

Figure 4. Surface weather map valid at 12Z (6:00 am CDT) on Monday, November 10, 1975. The Great Lakes storm that sank the Edmund Fitzgerald later in the day was then located over the Upper Peninsula of Michigan. The storm’s central pressure later fell to 975 millibars. Image credit: CIMSS Weather Blog.

Hurricane Extreme Weather

Kate Forms near Bahamas; Megh Heads toward Yemen Coast after Battering Socotra Island

By: Bob Henson and Jeff Masters , 5:23 PM GMT on November 09, 2015

Kate Forms Near Bahamas; Megh Heads Toward Yemen Coast after Battering Socotra Island

Tropical Storm Kate formed on Monday morning near the Central Bahamas, an unusual occurrence for November during an El Niño year (see below). At 10 am EST Monday, Kate was located about 15 miles east-northeast of Cat Island, moving northwest at 15 mph. The most recent Hurricane Hunter flight confirmed flight-level winds of 50 knots and SFMR surface winds of 40-42 knots, which led NHC to bump up Kate’s top sustained winds slightly to 40 knots (45 mph) in its 10 am advisory. Kate is not the most organized-looking tropical storm, with little evidence of spiral banding and only a ragged cluster of moderately strong convection (showers and thunderstorms) around its small center. Outflow near the top of Kate appears relatively healthy, though.

Figure 1. Enhanced infrared image of Tropical Storm Kate at 1515Z (8:15 am EST) Monday, November 9, 2015. Image credit: NOAA/NESDIS.

Kate should be able to maintain its named status for at least a day or two as it chugs past the Bahamas toward the northwest and north, well off the U.S. East Coast. After a season of relentlessly high wind shear across much of the tropical Atlantic, the shear values are quite low over Kate (5 – 10 knots). Sea surface temperatures near Kate are close to record-warm levels for the time of year: around 28°C (82°F), or 1-2°C above average. Kate is predicted by NHC to strengthen to a 65-mph tropical storm by Wednesday as it recurves to the northwest of Bermuda. Both the statistical SHIPS model and the dynamical HWRF model bring Kate close to the threshold of hurricane strength by Wednesday, with recent runs of the GFDL model even more bullish. Rather than decaying near the end of its life, Kate should then hold its own as a powerful post-tropical cyclone once it gets swept into an upper-level trough moving off the East Coast.

Tropical cyclones in the Atlantic: uncommon during El Niño Novembers
Kate is bucking the tide of El Niño by developing in November. Strong El Niño events typically bring the Atlantic season to an earlier-than-usual close, as the subtropical jet stream gets an increasing boost toward late autumn. If we look at those years since 1950 in which the October-to-December Niño3.4 index was in an El Niño state (at least +0.5°C), only about one in three of those years has produced a named storm in November. Outside of these El Niño years, almost every November since the Atlantic entered an active period in 1995 has seen at least one named storm. The only Atlantic hurricanes observed during El Niño Novembers since 1950 are Ida (2009), Florence and Gordon (1994), the “Perfect Storm” (1991), Frances (1986), and Martha (1969). There have been four years since 1950 with a strong El Niño in play during Oct-Dec (Niño3.4 index of at least +1.5°C). During those four years--1997, 1982, 1972, and 1965--only one named storm managed to develop in November: 1972’s Subtropical Storm Delta, which played out harmlessly far out in the central Atlantic.

Kate is the 11th named system of the 2015 Atlantic hurricane season, just below the 12 named systems observed in an average year from 1970 to 2010. The number of major hurricanes--two, Danny and Joaquin--is also comparable to the long-term average. However, there have only been three hurricanes, less than half of the average total of 6.5. Back in April, the forecast team from Colorado State University called for just 7 named storms, 3 hurricanes, and 1 intense hurricane, with an Accumulated Cyclone Energy (ACE) of 40. The April outlook from private forecasting firm Tropical Storm Risk, Inc., called for 11 named storms, 5 hurricanes, and 2 intense hurricanes, with a predicted ACE of 56. As of this morning, the Atlantic ACE value for 2015 was up to 57, still well below the season-long average of 110. The storm totals observed to date (11 named storms, 3 hurricanes, and 2 major hurricanes) fall within the 70%-likelihood brackets from NOAA’s outlook for the Atlantic season issued in late May.

Tropical Cyclone Megh headed towards a second landfall in Yemen
Tropical Cyclone Megh is threading the needle down the narrow Gulf of Aden in the Arabian Sea, but is weakening due to interaction with land, entrainment of dry air from the nearby deserts, and encounters with cooler patches of water upwelled last week by the passage of Tropical Cyclone Chapala. On Sunday, Megh powered ashore over Yemen's Socotra Island as a major Category 3 storm with 125 mph winds. Although news reports from the area remain sparse, it appears likely that Megh brought a second round of devastation to an island hard-hit the previous week by the passage of Tropical Cyclone Chapala. A BBC report cites AFP as reporting at least two deaths on Socotra due to Megh, with a spokesperson for the Socotra Environment Office reporting more homes destroyed by Megh than by Chapala. The latter cyclone passed just to the north of Socotra Island on November 2 when the storm was at Category 3 strength. Satellite images on Monday morning showed that Megh had suffered significant disruption of its cloud pattern, and by the time the storm reaches the south Yemen coast between Mukalla and Aden sometime on Tuesday, Megh will likely be a rapidly weakening tropical storm. Still, Megh will likely dump heavy rains over a desert region unused to seeing them, and widespread destructive flooding is likely near where the center comes ashore.

Figure 2. MODIS image of Tropical Cyclone Megh in the Gulf of Aden, approaching landfall in western Yemen, at 10:05 UTC November 9, 2015. At the time, Megh was a Category 1 storm with 85 mph winds. Image credit: NASA.

Figure 3. Tropical Cyclone Chapala as seen by the MODIS instrument on November 3, 2015 at 7:20 UTC. At the time, Chapala was making landfall in Yemen as a Category 1 storm with 75 mph winds. Image credit: NASA.

Twin major hurricanes in the Arabian Sea: unprecedented in the historical record
Megh is the second major Category 3 or stronger tropical cyclone to affect Yemen this month. Just a week ago, Tropical Cyclone Chapala took advantage of the the warmest waters ever recorded in the Arabian Sea at this time of year to intensify into a top-end Category 4 storm with 155 mph winds (1-minute average) on October 30, according to the Joint Typhoon Warning Center (JTWC). This made Chapala the second strongest tropical cyclone on record in the Arabian Sea, behind Category 5 Cyclone Gonu of 2007 (165 mph winds). Chapala went on to devastate Yemen's Socotra Island and mainland Yemen near the port city of Mukalla on November 3, killing at least eight people and causing widespread destructive flooding. According to NOAA's Historical Hurricanes tool, prior to this year, there had only been five major Category 3 or stronger tropical cyclones recorded in the Arabian Sea since accurate satellite records began in 1990 (an additional Category 3 storm occurred in 1977.) Thus, two major hurricanes in one month in the Arabian Sea is a remarkable occurrence. Also remarkable is the fact that Megh is the second tropical cyclone to hit Yemen (including Socotra Island) at hurricane strength this month. In the period with good satellite data (1990 – 2014), no tropical cyclones at tropical storm strength hit Yemen, though the nation had been hit by two tropical depressions--Tropical Depression Keila in 2011, and Tropical Depression Three in 2008. That storm was the second costliest natural disaster in Yemeni history, with a $400 million price tag. Longer-term records from 1891 - 2014 show Yemen has been hit by only two tropical storms and no hurricane strength storms; tropical storms hit the coast in May 1959 and May 1960. However, according to Dallas (1891) a tropical cyclone entered the Gulf of Aden in June 1885 and a ship measured 943 mb, making the storm likely to be at least at Category 3 strength (see Membery, 2002, Weather. H/T to Cuban meteorologist Alejandro Adonis Herrera G. for this link.)

Figure 4. Surface analysis of the June 2, 1885 major hurricane in the Gulf of Aden. A ship measured a pressure of 943 mb. Image credit: Membery, Weather, July 2002: "Monsoon tropical cyclones: Part 2."

Air pollution blamed for an increase in strength of Arabian Sea tropical cyclones
The Arabian Sea doesn't get many tropical cyclones since it is small; furthermore, the Southwest Monsoon keeps tropical cyclones from forming much of the year, allowing only a short season from May to early June before the monsoon arrives, and another short season in late October through November after the monsoon has departed. Strong Arabian Sea storms are rare due to high wind shear and copious dry air from the deserts of the Middle East, with just three Category 4 or 5 storms ever recorded--Gonu in 2007, Phet in 2010, and Chapala in 2015. Arabian Sea tropical cyclones during the pre-monsoon period in May and June have become stronger over the past 30 years owing to a reduction in vertical wind shear brought about by dimming of sunlight from air pollution particles primarily emitted in India, said Evan et al. in a 2011 paper published in the journal Nature. The authors did not study how post-monsoon tropical cyclones in October and November, like Tropical Cyclones Chapala and Megh, might be impacted by air pollution. However, the authors did speculate that continued growth in air pollution emissions might also reduce wind shear in the post-monsoon October-November period, and wrote, "In such a case it is plausible that very intense tropical cyclones, which have so far been limited to the pre-monsoon period, could begin to emerge in the post-monsoon season as well."

El Niño matches weekly record from 1997-98
The blockbuster El Niño event of 2015 continues to gather strength in the tropical Pacific. In its weekly update issued on Monday, NOAA reported that the Niño3.4 sea-surface temperature over the past week was 2.8°C above average. This is the highest weekly value reached to date during the current El Niño event, and it matches the peak departure from normal of 2.8°C observed in late November 1997 during the record-setting 1997-98 El Niño. The weekly value could rise a bit more in the next several weeks before leveling off and then slowly dropping through early 2016, as expected from the classic evolution of major El Niño events and in line with indications from forecast models. Even as the Niño3.4 values gradually decline, El Niño’s influence on Northern Hemisphere weather should actually peak during the winter months, as the polar and subtropical jet streams feel the maximum seasonal influence from the El Niño configuration in the tropics. See our Weather Underground El Niño forecast page for much more background on what to expect from this El Niño event, both nationally and globally.

Figure 5. Forecasts issued in mid-October by dynamical and statistical models for the Niño3.4 sea-surface temperature (SST) for nine overlapping 3-month periods. Note that the expected skills of the models, based on historical performance, are not equal to one another. The skills also generally decrease as the lead time increases. Forecasts are typically most accurate from June to December and least accurate from February to May. Differences among the forecasts of the models reflect both differences in model design, and actual uncertainty in the forecast of the possible future SST scenario. Image credit: International Research Institute for Climate and Society/NOAA Climate Prediction Center.

Figure 6. A man dives into Lake Geneva on an unusually warm day in Saint-Prex on Sunday, November 8, 2015, as record-breaking temperatures for the month of November hit Switzerland. Image credit: Fabrice Coffrini/AFP/Getty images.

Heat records tumble over Southeast US, Europe, Japan
November is thumbing its nose at the calendar when it comes to unusually warm temperatures across several parts of the Northern Hemisphere. Much of the Southeast U.S., and especially Florida, have experienced their warmest stretch of weather ever recorded in the first week of November. Uncommon November warmth has also bathed Europe: high temperatures on Sunday ranged from the 60s to near 80°F over much of France and Switzerland, with readings as warm as 30°C (86°F) in parts of Spain and Japan. Stay tuned for details: WU weather historian Christopher Burt is about to dive into the many monthly heat records being established this month in North America, Europe, and Asia, as the planet hurtles toward what is virtually certain to be its warmest year since record keeping began more than a century ago.

Bob Henson and Jeff Masters

Hurricane El Niño Heat

Déjà Vu: Category 3 Megh Slams Yemen Island; Bahamas Disturbance 94L May Develop

By: Jeff Masters , 5:57 PM GMT on November 08, 2015

Tropical Cyclone Megh powered ashore over Yemen's Socotra Island on Sunday morning as a major Category 3 storm with 125 mph winds. Megh could well have been a Category 4 storm at landfall, since satellite estimates of small storms like Megh are subject to large errors. Megh's passage over the island has disrupted the storm some, and the Joint Typhoon Warning Center (JTWC) estimated the storm's peak winds at 115 mph at 7 am EST Sunday. Interaction with land, entrainment of dry air from the nearby deserts, and encounters with cooler patches of water upwelled last week by the passage of Tropical Cylcone Chapala should continue to weaken Megh. By the time it reaches the south Yemen coast between Mukalla and Aden sometime on Tuesday, Megh will likely be at tropical storm strength.

Figure 1. MODIS image of the eye of Tropical Cyclone Megh making landfall on Yemen's Socotra Island on November 8, 2015. At the time, Megh was a Category 3 storm with 125 mph winds. Image credit: NASA.

Figure 2. Tropical Cyclone Chapala as seen by the MODIS instrument on November 1, 2015. At the time, Chapala was passing just north of Yemen's Socotra Island as a Category 3 storm with 120 mph winds. Image credit: NASA.

Twin major hurricanes in the Arabian Sea: unprecedented in the historical record
Megh is the second major Category 3 or stronger tropical cyclone to affect Yemen this month. Just a week ago, Tropical Cyclone Chapala took advantage of the the warmest waters ever recorded in the Arabian Sea at this time of year to intensify into a top-end Category 4 storm with 155 mph winds (1-minute average). This made Chapala the second strongest tropical cyclone on record in the Arabian Sea, behind Category 5 Cylcone Gonu of 2007, the only Category 5 storm ever recorded in the Arabian Sea (Gonu peaked at 165 mph winds). Chapala went on to devastate Yemen's Socotra Island and mainland Yemen near the port city of Mukalla on November 3, killing at least eight people and causing widespread destructive flooding. According to NOAA's Historical Hurricanes tool, prior to this year, there had only been five major Category 3 or stronger tropical cyclones recorded in the Arabian Sea since accurate satellite records began in 1990, and an additional Category 3 storm that occurred in 1977. Thus, two major hurricanes in one month in the Arabian Sea is a remarkable occurrence.

Figure 3. Latest satellite image of 94L.

94L could develop into a tropical depression near the Bahamas
A well-organized area of heavy thunderstorms near the Southeast Bahamas and Turks and Caicos Islands (Invest 94L) is associated with an area of low pressure headed west-northwest at about 15 mph. Satellite loops on Sunday morning showed 94L had a modest degree of spin, and a moderate-sized area of heavy thunderstorm activity. Wind shear was a moderate 10 - 20 knots over 94L, and water temperatures were record-warm for this time of year, near 29°C (84°F). The 8 am EDT Sunday run of the SHIPS model predicted that wind shear near 94L would remain moderate through Wednesday and ocean temperatures would be above the 80°F threshold for tropical storm formation--conditions which should allow 94L to develop into a tropical depression by Wednesday, though waer vapor satellite loops show that there is some dry air to the west of 94L that could slow down development. In their 1 pm EST Sunday Tropical Weather Outlook, NHC gave 94L 2-day and 5-day odds of development of 70%. The disturbance should continue heading west-northwest through Monday afternoon, spreading heavy rain showers into the Central Bahamas. By Monday night or Tuesday morning, 94L should turn sharply to the north just before reaching the northwest Bahamas, as a trough of low pressure passing to the north pulls the disturbance northwards. This motion should keep 94L from having any direct impacts on the U.S. East Coast. 94L will then turn to the north-northeast or northeast by Tuesday afternoon, and could bring heavy rains to Bermuda on Wednesday. About half of the members of the GFS and European ensemble models develop the system into a tropical depression, though the operational versions of these models were lukewarm on the development prospects. Should 94L intensify into a tropical storm, it would be called Tropical Storm Kate. A hurricane hunter flight is scheduled to investigate 94L on Monday morning.

Jeff Masters


Climate Change and Extreme Weather: 32 Takes on 28 Events from 2014

By: Bob Henson , 6:18 PM GMT on November 06, 2015

The science of deciphering how much long-term climate change influences shorter-term weather and climate events continues to blossom. On Thursday, the American Meteorological Society (AMS) released its fourth annual special issue of the Bulletin of the AMS devoted to these attribution studies. Launched in 2012 as an experiment, the project hit a nerve: researchers and the public were both intensely interested in the connection between human-produced greenhouse gases and high-profile, high-impact weather. This year’s batch of studies, which focuses on events from 2014, is the largest yet: a total of 32, including more than 100 researchers from 20 countries looking at 28 extreme weather and climate events from all seven continents. New topics this year include tropical cyclones, forest fires, and anomalies in sea surface temperature and sea level pressure. For about half of the events studied in this year’s AMS report, scientists found that human-induced climate change played a measurable role in making the event stronger and/or more likely.

Figure 1. Icons denoting the locations and nature of the 28 events examined in the 2015 special issue of BAMS devoted to climate change attribution for extreme events from the year 2014. ETS = extratropical storms; SST = sea surface temperature; MSLP = mean sea level pressure. Image credit: NOAA/NCEI.

Each year the project editors invite researchers from around the world to choose a particular event and examine it through the lens of climate change and its potential influence. Because the report is an open digest of sorts, it includes a variety of techniques in which particular events are put in a larger context using models and observations. Attribution science remains a young field, and there’s still room for experimentation.

A couple of U.S. highlights
There is far too much interesting science in this BAMS report to cover in a short blog post. For those most interested in U.S. weather, the report has plenty to chew on, including coverage of 2014’s burst of hurricane activity near Hawaii; the year’s drought-stoked wildfire season in California; the active winter storm track across much of North America in 2013-14; that winter’s Midwestern cold; and the chilly conditions that prevailed over much of the East. Strikingly, each of these events recurred to at least some extent in 2015. This is itself a fascinating phenomenon, one that goes unaddressed in the report--but that’s understandable, given that the report’s mandate is to focus on one year at a time. Below is some more detail on a couple of the U.S. events that I found particularly interesting.

Figure 2. Hurricane Iselle, with 90 mph winds, and Hurricane Julio, with 75 mph winds, steam west-northwest towards the Hawaiian Islands in this GOES-West image taken at 8 pm EDT Wednesday, August 6, 2014. Image credit: NASA/Goddard Space Flight Center.

Hawaiian hurricanes
Three tropical cyclones passed within 500 kilometers (300 miles) of the Hawaiian Islands in 2014: Iselle, Julio, and Ana. A research team led by Hiroyuki Murakami (NOAA Geophysical Fluid Dynamics Laboratory) used GFDL’s Forecast-oriented Low Ocean Resolution model (FLOR) to simulate hundreds of hurricane seasons with and without the influence of human-produced greenhouse gases. Even the amount of greenhouse gas already present by 1990 was enough to boost the odds threefold of getting at least one tropical storm or hurricane within 500 kilometers (300 miles) of the Hawaii coastline, compared to the simulations with preindustrial (year-1860) levels of greenhouse gas. One would not necessarily have expected a big year for tropical cyclones near Hawaii in 2014, given the unfavorable values of Pacific and Atlantic oscillations (IPO, AMO, and PDO) combined with a moderately favorable El Niño state. However, the years in which this blend of factors showed up in the greenhouse-boosted simulations produced a 340% greater chance of activity near Hawaii. “It is possible that global warming increased the odds of the extremely large number of Hawaiian TCs in 2014, in combination with the moderately favorable condition of El Niño,” write the authors. They add: “The ensemble experiments with FLOR indicate a continued increasing probability of active seasons around Hawaii over the next few decades...although there will be substantial modulation on interannual and decadal time scales from internal variability.”

Figure 3. The Las Pulgas Fire lights the night on May 16, 2014 at Camp Pendleton, California. The fire was one of three large wildfires in San Diego County that scorched more than 26,000 acres. Image credit: David McNew/Getty Images.

California fire risk
A group led by Jin-Ho Yoon (Pacific Northwest National Laboratory) studied 2014’s highly destructive Western US. fire season. Their results pointed in the same direction as several recent studies emphasizing the role of long-term warming in boosting drought impact and fire risk.The group drew on satellite analyses of burned area together with the Keetch-Byram Drought Index (KBDI), which incorporates both temperature and precipitation. It’s well known that decades of forest preservation coupled with population growth have helped bump up fire risk throughout the West. This study looks directly at how a warming climate affects fire risk by using the Community Earth System Model (CESM1) to directly calculate the KBDI and the probabilities of wildfire during preindustrial, recent, and future climates. Natural climate variation will make some years more fire-friendly than others, but this study found that climate change will push the overall threat beyond the range of natural variability over the next decade or so, as measured in three ways: the annual average KBDI, the amount of land under extreme fire risk, and the number of extreme fire-danger days per year. Interestingly, this is all despite the fact that the CESM1 produces a somewhat wetter California climate later this century (in line with several other recent climate projections). There’s no telling whether any given high-risk year will actually produce catastrophic fire: that depends on day-to-day weather, as well as factors such as the aggressiveness of firefighting, the presence or absence of arsonists, and sheer luck. The authors weren’t able to rule out natural variability as a factor in 2014’s highly destructive fire season. However, they did conclude that “man-made global warming is likely one of the causes that will exacerbate the areal extent and frequency of extreme fire risk.”

Cold in the Midwest and East
A pair of studies looked at the frigid winter of 2013-14 and found no evidence that human-produced climate change was responsible. Both studies concluded that, if anything, there seems to be less rather than more variability in winter temperatures as time goes by. The Midwest team, led by Klaus Wolter (CIRES/University of Colorado Boulder), focused on a broad area they call the “greater Upper Midwest,” or GUM, that extends from the eastern Dakotas to New York and Pennsylvania. Using a variety of simulations from 30 climate models, the group focused on the odds of getting a winter as cold as 2013-14 in today’s climate vs. the colder climate that was in place in the late 1800s, when human-produced greenhouse gases were far less prevalent. A winter like 2013-14 would have been expected about once per decade in the late 19th century, but in today’s climate, such a winter is now “extraordinarily unlikely,” as the authors put it--perhaps only once in every few hundred years. I asked Wolter about the recurrence of intense cold and snow over the eastern GUM region in 2014-15, which seems to fly in the face of the long odds found in his study. Wolter noted that snow cover is a big factor, since early snowfall helps set the stage for a cold winter. “The models are telling us that snow cover should be declining so rapidly that this kind of cold winter is on its way out. But the observations are giving us either no trend or even an upward trend in early winter snow cover.”

Figure 4. Snowfall plasters the streets of New York on February 13, 2014, part of a winter storm that knocked out power to more than a million homes and business across the eastern U.S. Image credit: Spencer Platt/Getty Images.

The study of Eastern cold, led by Laurie Trenary (George Mason University/COLA), focused on whether increased variability from 1950 to 2014 could explain the winter chill of 2013-14 in three regions: north-Atlantic (Pennsylvania northward), mid-Atlantic (from the Mason-Dixon line to North Carolina), and south Atlantic (Alabama, Georgia, South Carolina, and Florida). The team used several diverse measures in each region, including the coldest single January-to-March reading in each year, the variability of daily temperature within each winter, and the number of days per winter that fall into the coldest 10% in the long-term climatology. The winter of 2013-14 stands out dramatically in that final measure, ranking above any other year on record in all three regions. Otherwise, though, the findings are consistent: “the variability of winter daily temperature, and therefore of the range of realized temperature, has been decreasing for the past six decades.” Another wrinkle is that no significant change in the variability showed up when the period 1950-2014 was simulated by 12 leading global climate models as part of the Climate Model Intercomparison Project (CMIP). However, the observed drop in variability is still within the confidence interval of all models for the north and mid-Atlantic and about half the models for the south Atlantic.

The authors present their findings as an alternative to the “Francis hypothesis”--the concept put forth by Jennifer Francis (Rutgers University) and colleagues that a weaker, more meandering jet stream attributed to polar warming and reduced Arctic sea ice is leading to greater extremes and more “stuck” weather patterns. If anything, these authors suggest, high-latitude effects might be tamping down extremes rather than goosing them. “The decrease in variance is a plausible consequence of polar amplification of global warming, since a decrease in the pole-to-equator temperature gradient reduces the strength of fluid dynamical instabilities,” they write. As with the Midwestern study, this one does not address the recurrence of severe cold during the winter of 2014-15, but Trenary told me that NOAA/NCEP reanalysis data into 2015 maintains the decreasing long-term trend in winter temperature variability over the study area. “There are a number of open research questions,” she added. “For example, it would be interesting to look at the spatial changes in wintertime temperature variability across the US and see if there is any relation between the jet-stream variability and spatial characteristics of wintertime temperature variability. Fundamentally, it’s important to understand why these observed changes in wintertime temperature variability are occurring.”

Commentary: A work in progress
Climate change is a sprawling, long-term phenomenon that doesn’t always fit neatly into 365-day boxes. Its influence is obvious when you’re looking at slow-burn phenomena, such as the year-over-year rise in global sea levels or the gradual shift poleward in planting zones. The closer you get to a single weather/climate extreme, the more challenging it can be to connect the dots--and sometimes the dots lead you to preliminary, less-than-dramatic answers. Most of the temperature-related extremes in this year’s BAMS report were found to have a climate-change link of some type, while the connections with rain and snow extremes were less consistent and harder to ferret out. Drought, in particular, is a tough nut to crack, largely because it includes so many natural and human cofactors and because it can be defined in multiple ways.

In a press packet released on Thursday, lead editor Stephanie Herring (NOAA National Centers for Environmental Information) emphasized one crucial caveat: the absence of a clear climate-change influence in any particular study doesn’t prove that no influence exists. “Any of the following could explain the absence of a signal: there was no human influence on the event; the particular factors investigated were not influenced by human-caused climate change; [or] the human influence could not be identified with the scientific tools available today.”

Lurking in the background of any attribution study is the natural variation inherent in our weather and climate system. Researchers go to great lengths to separate any influence of climate change from the kinds of ups and downs one would expect in a climate that didn’t have ever-increasing greenhouse gases. This year, the states of New York and Vermont had their coldest January-to-March period since records began in 1895, with all of the Northeast in their top-ten coldest. Surely, the odds of getting such widespread, persistent, intense cold over this large an area in a warming climate must be phenomenally low--but sometimes, even very unlikely things happen. This paradoxical, high-impact event gets my vote for inclusion in next year’s BAMS attribution report. Stay tuned!

We’ll be keeping an eye on Cyclone Megh and on the potential for tropical development in the Gulf of Mexico and the Atlantic. See Jeff Masters’ post from earlier today for more on these systems.

Wunderblogger Steve Gregory has a new Friday afternoon post, Stormy Pattern As Arctic Cold Develops - Hints of Pattern Change.

Bob Henson

Climate Change

Two Disturbances to Watch in the Atlantic; Megh and 96B Active in the North Indian

By: Jeff Masters , 2:31 PM GMT on November 06, 2015

Cyclonic Storm Megh continues to slowly organize over the Arabian Sea as the storm heads west towards Yemen and Somalia. As of 7 am EST Friday, the Joint Typhoon Warning Center put Megh's winds at 50 mph, and predicted the storm would take advantage of low wind shear and warm ocean waters near 28°C to intensify into a Category 1 storm by Sunday--although Megh could encounter some cooler patches of water upwelled last week by the passage of Tropical Cyclone Chapala. Cyclone Chapala left at least 8 fatalities and more than 200 injuries and destroyed dozens of structures in Yemen, including Socotra Island, which may receive a direct hit from Megh. As explained in more detail in Thursday's post, Megh may be a threat to Somalia, which has had more experience with tropical cyclones than Yemen in recent years.

Figure 1. MODIS image of Tropical Cyclone Megh over the Arabian Sea on November 6, 2015 at 09:15 UTC. Image credit: NASA.

A second tropical cyclone in the North Indian Ocean this weekend?
The North Indian Ocean may witness a very rare event this weekend: the existence of two simultaneous tropical cyclones in November--one in the Bay of Bengal and one in the Arabian Sea. Recent satellite loops of Invest 96B in the Bay of Bengal show that this area of heavy thunderstorms moving westwards towards Sri Lanka and the east coast of India has acquired some spin, and the European model shows this disturbance developing into a tropical depression by early next week. A 2011 study by Evan and Camargo, A Climatology of Arabian Sea Cyclonic Storms, found that between 1979 - 2008, only 1986 saw November tropical cyclones form in both the Bay of Bengal and the Arabian Sea. The authors theorized that favorable conditions for development in the Arabian Sea tend to cause unfavorable conditions over the Bay of Bengal, and vice-versa.

Two Atlantic areas of disturbed weather to watch
An area of heavy thunderstorms near the northern Lesser Antilles Islands extending eastwards several hundred miles is associated with a tropical wave interacting with an upper-level trough of low pressure. Wind shear is a high 20 - 30 knots over the region, so development is not expected for the next two days while the disturbance moves west-northwest at about 10 mph. However, on Sunday, when the disturbance will be near the Dominican Republic and Southeast Bahamas, wind shear is expected to drop to the moderate range, 10 - 20 knots, and some development could occur. In their 8 am EDT Friday Tropical Weather Outlook, NHC gave the wave 2-day and 5-day odds of development of 0% and 30%, respectively. The disturbance should head north by Tuesday and then northeast by Wednesday, and could bring heavy rains to Bermuda by the middle of the week. A number of members of the GFS and European ensemble models develop the system into a tropical depression.

A broad area of low pressure over the Yucatan Peninsula and the adjacent waters of the Gulf of Mexico is producing disorganized shower activity, and will move west-northwestward into the southwestern Gulf of Mexico by Saturday. Wind shear is moderate at 10 - 20 knots, which may allow some slow development until the disturbance gets entangled with a cold front early next week. In their 8 am EDT Friday Tropical Weather Outlook, NHC gave the wave 2-day and 5-day odds of development of 20% and 20%, respectively. Very few members of the GFS and European ensemble models develop the system into a tropical depression, and the ones that do show the disturbance staying weak and stuck in the extreme southern Bay of Campache.

The science of deciphering how much long-term climate change influences shorter-term weather and climate events (attribution studies) continues to blossom. On Thursday, the American Meteorological Society (AMS) released its fourth annual special issue of the Bulletin of the AMS devoted to these attribution studies. Bob Henson will offer his take on the studies in a post later today.

Jeff Masters


Cyclone Megh Forms in Indian Ocean; Balmy Fall Weather over Eastern U.S.

By: Bob Henson , 8:34 PM GMT on November 05, 2015

In what seems like an instant-reply development just days after the historic trek of Cyclone Chapala, Cyclonic Storm Megh has formed over the central Arabian Sea, again heading in the general direction of Yemen and Somalia. As of 15Z (10:00 am EDT) Thursday, the India Meteorological Department placed Cyclone Megh near 13.9°N, 63.7°E, or about 1080 km east-southeast of Salalah, Oman. Top 1-minute sustained winds from the Joint Typhoon Warning Center are at minimal tropical-storm strength, 40 mph. Large bands of convection are wrapping into Megh’s gradually organizing center. The amount of moisture in the atmosphere surrounding Megh appears to be at least as much as during Chapala’s formative stage, as seen in this NOAA/NESDIS loop of precipitable water (the amount of water vapor over a given point).

Figure 1. VIIRS image of Megh in its formative stages over the Arabian Sea on November 4, 2015. Image credit: NOAA.

Figure 2. Enhanced infrared image of Cyclone Megh, with icons showing forecast track for the next two days. Image credit: NOAA/NESDIS.

Megh is moving just south of due west around the base of an broad upper-level high that should put the cyclone on a steady west-southwest track for the next several days. Vertical wind shear is low (10 knots or less), and sea-surface temperatures are at record levels across the North Arabian Sea, although Megh could encounter some cooler patches of water upwelled by the passage of Chapala. The 15Z forecast from JTWC brings Megh close to hurricane strength as it passes just south of Socotra, the remote Yemeni island slammed by Chapala’s south side. JTWC’s forecast track then nicks the north end of Somalia and brings Megh into the Yemen coast as a minimal tropical storm, while the IMD forecast track keeps Megh a bit further north. The 12Z HWRF model paints a true deja-vu scenario, with Megh passing just north of Socotra as a Category 3 storm, then making landfall on the central Yemen coast as a strong tropical storm. Given the unusually favorable conditions, I would not be surprised to see Megh reach at least Category 1 or 2 strength, assuming it does not pass directly over Chapala's track.

Cyclone Chapala left at least 8 fatalities and more than 200 injuries and destroyed dozens of structures in Yemen, including Socotra. About 3000 families were displaced, according to a recent AFP report. Humanitarian aid, including food and medical supplies, has been flowing from Oman, the United Arab Emirates, and the World Health Organization to Yemen, where the ongoing civil war has complicated relief efforts.

Aside from Chapala, only two other tropical cyclones are known to have made landfall in Yemen in the last 125 years: a destructive tropical depression in 2008, which caused an estimated 200 deaths, and a tropical storm-strength cyclone in 1960. The impact of the 2008 cyclone was magnified by heavy rains that had fallen just days earlier from the remnants of another tropical cyclone. Likewise, if Megh did make landfall on a track like Chapala’s, the potential for flooding this time could be even worse. NASA satellite analyses indicate that Chapala’s rains were considerably less than models had predicted on the Yemen mainland, but still on the order of 8-16”, with perhaps as much as 24” on Socatra.

Figure 3. Evacuees walk with their belongings in the area around Sinujiif, Somalia, on November 14, 2013, after a ferocious storm and days of heavy floods associated with a tropical depression that led to more than 100 deaths in the country’s northeastern Puntland region. Image credit: Mohamed Abdiwahab/AFP/Getty Images.

Somalia has had more experience with tropical cyclones than Yemen in recent years. The deadliest was a tropical cyclone (making landfall at tropical storm strength, according to JTWC) that moved onto the east-central Somali coast on November 22, 2013. The cyclone triggered rains that took at least 162 lives, many of them children and elderly residents who died of exposure. This storm (TD ARB01) struck just days after Typhoon Haiyan, so it gained relatively little media attention. As Jeff Masters noted at the time, several other tropical cyclones have hit Somalia in modern records: Murjan (October 2012), Agni (December 2004), ARB01 (November 1994), ARB04 (December 1992), Tropical Cyclone 4B (December 1984), and TS 1 (May 1984).

All of the above were late-season storms except for 1984’s TS 1, which made landfall on the north coast of Somalia after becoming the only North Indian cyclone on record to cross the entire Gulf of Aden.

Figure 4. Tracks of all tropical cyclones that have made landfall in Somalia since the Joint Typhoon Warning Center began keeping records of storm intensity for this region in 1972. See text at left for more on each storm. Image credit: Phil Klotzbach, Colorado State University.

Caribbean disturbance to send moisture into Gulf of Mexico
For the next five-day period, the National Hurricane Center puts 20% odds on development of a tropical wave now generating extensive showers and thunderstorms over the northwest Caribbean and southern Gulf of Mexico. Moderate wind shear (10-20 knots) and interaction with the Yucatan Peninsula will limit any development for the next day or two. Another brief window will open as the system moves into the Bay of Campeche, where weaker wind shear prevails.

Extreme warmth for early November in Michigan, Florida
Much of the eastern two-thirds of the United States was bathed in unusual autumn mildness at midday Thursday, with temperatures in the 70s and 80s from Texas to Michigan and east to New Hampshire. All-time highs for November were notched on Wednesday at several far-flung locations, including Flint, MI (80°F) and Tampa, FL (92°F). The low since midnight at Traverse City, MI, was a summerlike 62°F; if that reading holds till midnight Thursday night, it’ll be the lakeside city’s warmest November minimum on record. Most of Florida has seen a solid week of record- or near-record heat. In Tallahassee, the first four days of November were a full 4°F warmer than any other four-day November stretch in the city's weather history. My vote for the most impressive spot is Key West, where the last time the temperature dipped below 80°F was nearly a week ago--on Friday, October 30. Each night since Halloween has set a record-warm minimum for the date of either 80°F or 81°F. The 81°F readings on Sunday and Monday are the warmest November daily minima ever observed in Key West, where recordkeeping began in 1872. We can expect more daily and monthly records to tumble over the next couple of days before the mild weather over most of the eastern U.S. is pushed offshore by a seasonably strong cold front, accompanied in many areas by strong thunderstorms. A tornado watch was in effect Thursday afternoon over eastern Oklahoma and north Texas, and flash flooding is again a threat late Thursday into Friday from northeast into southern TX.

The associated upper-level storm has brought welcome snowfall across much of the mountainous West, including the recently snow-starved Sierra Nevada. Even Flagstaff, AZ, got in on the act, with almost a foot of snow piling up there. Strong westerly flow at upper levels will bring another powerful storm into the West early next week, with more heavy rains possible later next week in the beleaguered south-central states.

Figure 5. General view of a flooded area in the city of Villahermosa in Mexico’s Tabasco state on November 1, 2007. More than 1 million people were affected by the flooding across Tabasco and Chiapas. Image credit: Gilberto Villasana/AFP/Getty Images.

Looking back at the great November 2007 flood in southern Mexico
Norman Avila, a software engineer based in Guatemala City and a longtime Weather Underground member, is wrapping up a three-week stint at WU headquarters in San Francisco as part of a fellowship sponsored by the International Center for Journalists. The ICFJ brings journalists, technologists and digital entrepreneurs from Latin America to the United States to train and embed in U.S. digital organizations. While on site, Norman has been meeting with various WU staff, gaining insights that he hopes to apply to his own Spanish-language website,, which is focused on natural disasters in Central America. Norman has also found time to produce his first blog post for WU, which analyzes the catastrophic flood that struck Mexico's Tabasco state in the fall of 2007. As much as 80% of Tabasco was estimated to be under water at the height of the flood, which affected more than a million people. Thanks for contributing to WU, Norman!

Bob Henson

Hurricane Extreme Weather Flood

Patricia and Recent U.S. Hurricanes: What Makes a Storm “Big”?

By: Bob Henson , 3:47 PM GMT on November 04, 2015

Among its many history-making attributes, Hurricane Patricia will go down as one of the least deadly Category 5 hurricanes to make landfall in the Western Hemisphere since modern records began. Only 8 direct and 5 indirect fatalities have been reported to date. Among landfalling Category 5 storms in the Atlantic and Northeast Pacific, Patricia is on par with the low death tolls of Hurricanes Dean (2007) and Anita (1977). Patricia’s minuscule size played a big role in the low death toll, and it also serves as a vivid contrast to the weaker but larger hurricanes that have struck the United States in recent years. It’s now been more than ten years since the U.S. has seen a major hurricane landfall (Category 3, 4, or 5). The last one was Wilma, which struck Florida on October 24, 2005. Still, in the decade since Wilma, the nation has incurred more than $100 billion in hurricane-related damage. Most of this was produced by two massive storms that arrived on U.S. shores below Category 3 strength: Ike (2008) and Sandy (2012).

Figure 1. Hurricane Patricia as seen from the International Space Station at midday on Friday, October 23, 2015. Image credit: Scott Kelly/NASA.

Simply put, people tend to assume that a strong hurricane is also a large one, and vice versa. When I was interviewed on the PBS NewsHour during the height of Patricia, the first question asked by William Brangham was, “How did this storm get so big so fast?” NPR’s David Greene employed the same lead-in question in his interview with researcher Kristen Corbosiero (University at Albany) following Patricia’s landfall. These are smart, solid journalists, so I have a feeling their queries reflect a much broader sense among nonspecialists that a Category 5 hurricane is inherently huge--which is certainly not the case.

Table 1. Size and strength of Wikipedia’s five most damaging hurricanes in U.S. history)--Katrina, Sandy, Andrew, Ike, and Wilma--listed in order of damages (not adjusted for inflation or changes in wealth], as well as this year’s Hurricane Patricia in Mexico. The radius of hurricane-force winds was drawn from the last NHC public advisory issued before landfall. Maximum winds are those at landfall, as analyzed in the NHC HURDAT database. Although Sandy was classified as a post-tropical cyclone just before it made landfall, subsequent analysis confirmed that hurricane-force winds did come ashore.

Lessons from Sandy and Ike
The assumption that hurricane strength is more important than size may have already taken a toll of its own. It became clear as Sandy approached the Atlantic coast that its wind field would be enormous, likely funneling a dangerous storm surge into the New York region. But media attention revolved largely around Sandy’s peak wind speeds and how much those might decrease by landfall. Likewise, Hurricane Ike’s “demotion” to Category 2 strength before landfall on the upper Texas coast may have played a big role in the comparatively tepid response to its approach. Based on dozens of post-storm interviews, Rebecca Morss and Mary Hayden (National Center for Atmospheric Research, or NCAR) concluded: “Given the storm surge and damage Ike caused, a number of interviewees did not feel that Ike’s classification on the Saffir-Simpson scale adequately communicated the risk Ike posed.”

With huge storms like Sandy and Ike, the wind field often expands as the peak winds decrease, which means that the wind-generated surge can actually continue to grow. The vast majority of U.S. damage from both Sandy and Ike was surge-related, as was the case for Katrina--yet another hurricane that produced less wind damage than feared, but more surge damage than expected.

Figure 2. Aircraft-based surface wind analyses for Hurricane Sandy (left) at 18Z (2:00 pm EDT) on October 29, 2012, and Hurricane Patricia (right) at 18Z on October 23, 2015. Both images are from roughly five hours before landfall. Although Patricia’s maximum sustained winds are more than 40 mph stronger, Sandy’s wind field is far broader, as evident in the much wider coverage of winds above tropical storm strength, or 34 knots (yellow), and 50 knots (red). Image credit: CIRA/RAMMB/CSU archives for Sandy and Patricia.

How the NHC handles hurricane size
For many decades, public advisories from the National Hurricane Center have included the radii of hurricane- and tropical-storm-force winds (65 and 34 knots, respectively). These numbers are rarely mentioned in the media, but NHC is starting to emphasize them more in their public-facing products, including the new “key messages” portion of the NHC forecast discussion. This distillation of bottom-line points earned much praise when used for the first time during Hurricane Joaquin. I asked James Franklin, the head of NHC’s Hurricane Specialist Unit, for his thoughts on the “size issue.”

“I saw lots of references to how big Patricia was, which was why we started talking about how small the area of really strong winds was in our key messages,” Franklin told me. “To me, the confusion seemed worse than normal with this particular case.”

Storm size was long omitted from hurricane data archives, in part because it can be difficult to reliably confirm the wind radii. It was only in 2004 that the NHC added hurricane size to its “best track” process, which produces a careful analysis of each landfalling hurricane archived in the center’s HURDAT database. “Although we didn’t feel fully comfortable with the accuracy of the best-track radii (and still don’t), the radii are something we forecast, and we thought that best-tracking them was an important step toward improved prediction,” said Franklin. Hurricane size is factored into the new storm-surge warning products being rolled out by NHC, as well as the wind-speed probabilities that are arguably more useful than the traditional “cone” in assessing potential impacts.

Figure 3. The narrow scope of Hurricane Patricia’s intense winds is evident in this graphic from the National Hurricane Center showing the probability of hurricane-force winds at a given point across the period from 8:00 am EDT Friday, October 23, to Wednesday, October 28. Image credit: NHC.

How researchers are tackling the problem
Only in the last decade or so have researchers paid closer attention to hurricane size, motivated in part by concerns about how tropical cyclones might change in a warming world. The widely used Accumulated Cyclone Energy (ACE) includes only the sustained winds and duration of a given hurricane, not its size. In a 2005 paper for Nature, Kerry Emanuel (Massachusetts Institute of Technology) introduced the concept of power dissipation, which includes storm size as well as peak winds. Emanuel later developed the simpler power dissipation index (PDI), the cube of the maximum winds analyzed every six hours across a storm’s lifetime. A group led by Vasu Misra (Florida State University, FSU) developed the Track Integrated Kinetic Energy (TIKE) index, which is similar to ACE while also specifying the width of near-surface sustained winds for each quadrant of the storm.

At NCAR, a team led by Greg Holland recently developed a Cyclone Damage Potential index that incorporates storm size and peak wind strength as well as forward motion. The idea is that faster-moving hurricanes typically produce less damage overall, despite the added component to the winds on the right-hand side. The CDP represents wind, wave, and ocean current damage offshore (e.g., to drilling rigs) as well as wind and coastal surge damage onshore. NCAR coauthor James Done stresses: “The CDP does not refer to actual damage in any specific circumstance. It is intended to provide easily assessed indications of the relative damage potential for individual storms--or collections of storms--over, for example, basins and seasons.”

Table 2 (below) shows the CDP values for the storms analyzed above in Table 1. As you can see, strong winds certainly push up CDP values. Patricia comes out on top among these six storms for damage potential, despite its tiny size. Yet the storm with the second-highest CDP is Ike, whose large size and slow forward motion compensated for its relatively modest winds. Of course, the CDP only provides a single guide as to how much damage a tropical cyclone is capable of. Any actual damage depends hugely on where the cyclone makes landfall, including the topography of the coastline (which dictates the amount of surge a given storm can produce) and the amount and type of coastal development.

Table 2. Hurricanes from Table 1, with forward motion included and Cyclone Damage Potential (see above) calculated. The values shown here for forward motion were drawn from the the last NHC public advisory issued before landfall, then converted into knots as part of the CDP calculation.

For its part, NHC prefers to handle each of the major hurricane threats (wind, storm surge, and rainfall) separately, using existing, well-known scales--the Saffir-Simpson Hurricane Wind Scale (SSHWS) for wind, feet for surge, and inches for rainfall--rather than by introducing new combined scales for public consumption. “As a shorthand measure of hurricane intensity, the SSHWS has served us well,” said James Franklin in a statement released by NHC on August 28. “It quickly conveys to the media and to the public the potential wind threat posed by an approaching storm to coastal populations, through an accompanying list of impacts that can be expected with winds of the various strengths. Beyond that, the SSHWS is one of several key parameters required to predict storm surge, the threat that primarily drives the evacuation decision making of state and local emergency managers….To widely promote an alternative scale, particularly one that was similar in structure to the SSHS, would confuse the public and the media, likely confuse some in the emergency management community, and ultimately undermine our efforts to keep people safe from tropical cyclones.”

Figure 4. The Colonial Bank building in Miami, shown here on October 26, 2005, was heavily damaged by Hurricane Wilma, which caused billions of dollars of damage and left millions without power. Image credit: Carlo Allegri/Getty Images.

Major hurricane or not, awareness is critical
In a future post, we’ll come back to the topic of how newer and older scales are being used to analyze how hurricanes might evolve in our warming world. For now, it’s worth emphasizing that large hurricanes striking at less than Category 3 strength have led to anything but a “drought” in U.S. hurricane damage, despite the lack of major landfalls. Even if the Category 3 cutoff is an arbitrary value--as emphasized in a just-published study led by FSU’s Robert Hart--it has big implications for public awareness, a point made well by Angela Fritz in a recent Capital Weather Gang post. So it’s still important to spread the word that less-than-major hurricanes need to be taken seriously.

There’s also no guarantee that steering currents will continue to guide major hurricanes into the open Atlantic, as we’ve seen so many times in the last decade. According to NHC science and operations officer Chris Landsea, “There does appear to be a contribution of having a long-wave trough set up in August-October along the US Atlantic seaboard for at least a few of these ten seasons, helping to force more recurvature than normal. I would leave it open as a possibility that decadal variability related to long-wave trough patterns has contributed to this major hurricane drought.”

Figure 5. Tracks of major Atlantic hurricanes (Category 3, 4, and 5) from the years 2006 through 2014. Sandy, Irene, and Ike are the only hurricanes on this map that went on to make a U.S. landfall. All three were weaker than Cat. 3 at that point, yet each one caused at least $10 billion in U.S. damage. (Not shown is 2008's Hurricane Gustav, which struck Louisiana as a Cat. 2 after weakening from high-end Cat 4 status.] Image credit: NOAA Historical Hurricane Tracks.

NCAR’s Kevin Trenberth stressed in an email: “The potential for major storms making landfall in the United States is always there.” He points to 2010 as a cautionary example, when five major Atlantic hurricanes managed to avoid the U.S. coast. Trenberth added: “I have always thought that landfall was overrated: it affects a small area right where the hurricane hits. The much more widespread effects are the heavy rainfalls that extend hundreds of miles inland.” Such was the case in 2011’s Hurricane Irene, whose downpours devastated parts of New England. Irene caused $16 billion in damage--making it America's seventh most costly hurricane, despite the fact that it hit at Category 1 strength. Even a tropical cyclone that never reaches hurricane strength can be catastrophic if it’s large and slow-moving--as with Tropical Storm Allison. Rainfall from Allison, which topped 40 inches near Houston, led to flooding that destroyed thousands of homes and caused 41 deaths.

As for Category 5 Patricia, its track happened to avoid any major population centers. Landsea cautioned against taking comfort in the United States from this close-to-best-case outcome. “Our vulnerability to hurricanes continues to worsen because of the steady to quick population growth along our coastal zones from Texas to Florida to the Carolinas to Maine. (It's also the case for our neighbors in the Caribbean and Central America.) Thus, we need to redouble our efforts in improved forecasts, long-term planning (building codes and land use zoning), and short-term planning (preparedness and evacuation efforts) to reduce our vulnerability to these extreme events.”

Bob Henson


Chapala Slams Yemen: First Hurricane-Strength Cyclone on Record

By: Bob Henson , 6:41 PM GMT on November 03, 2015

Residents of southern Yemen are assessing the damage after Cyclone Chapala brought dramatic flooding to the region on Monday night into Tuesday. According to the Indian Meteorological Department (IMD), Chapala made landfall near 14.1°N, 48.65°E between 01Z and 02Z Wednesday (4:00 - 5:00 am local time, or 8:00 – 9:00 pm Tuesday EST). This location is about 40 miles southwest of the coastal city of Mukalla (Al Mukalla), which was slammed by Chapala’s right-hand eyewall and some of its heaviest rains. Infrared satellite imagery shows a pronounced burst of convection (showers and thunderstorms) near and just west of Mukalla as Chapala made landfall.

Figure 1. A MODIS satellite view of Chapala as it approached the Gulf of Aden on Tuesday, November 2, 2015. Image credit: NASA EarthData.

Figure 2. Although Chapala’s eye was indistinct at landfall, thunderstorms intensified near its center as it came ashore, as shown in the pink and grey in this infrared satellite image taken near landfall (0100Z Wednesday, November 3, 2015). Image credit: Scott Bachmeier, CIMMS/SSEC/University of Wisconsin.

Yemen’s first hurricane-strength cyclone on record
IMD estimates Chapala’s peak winds at landfall as 65-70 knots (75-80 mph). India uses 3-minute sustained wind speeds, as opposed to the 1-minute average used by the National Hurricane Center. Guidance from NHC suggests that Chapala’s peak 1-minute winds would likely be several percent higher. Supporting the idea that Chapala made landfall at hurricane strength, the weather station at the Riyan airport, located about 20 miles northeast of Mukalla (Al Mukalla), recorded top sustained winds of 73 mph, gusting to 89 mph, before the sensor stopped reporting. Winds at Riyan were still increasing at the time, suggesting that hurricane-force winds probably occurred at some point in Chapala’s path during landfall. The nation experienced a destructive tropical depression in 2008 and a tropical storm-strength cyclone in 1960, but there are no hurricane-strength landfalls on record. Satellite records extend back to 1990, while a separate IMD database goes back to 1891.

Chapala moved mainly toward the west after landfall, hugging the Yemeni coastline, but the center is now making its way inland. At 15Z Wednesday (10:00 am EDT), the Joint Typhoon Warning Center placed Chapala’s center near 14.1°N, 47.5°E, or about 100 miles west of Mukalla. Based on the limited data available, JTWC estimated that Chapala still had sustained winds of 55 knots (62 mph).

Figure 3. An infrared view of Cyclone Chapala at 1530Z (10:30 am EST) Wednesday, November 3, 2015. Image credit: CIMMS/SSEC/University of Wisconsin.

As expected, the dry air and high terrain of southern Yemen has taken its toll on Chapala. Satellite imagery shows that the cyclone has become highly disorganized, with showers and thunderstorms decreasing and weakening around its ill-defined center. A pocket of more intense thunderstorms has popped up along the high terrain of Yemen’s west coast, well away from Chapala’s core circulation. Strong thunderstorms have also persisted in northeast Somalia, across the Gulf of Aden from Chapala. Villages along the Somalian coast have been affected by heavy rain and coastal flooding, according to Garowe Online. Prior to Chapala’s landfall in Yemen, the remote island of Socotra was hard-hit by the cyclone’s left-hand flank, with at least three fatalities reported by Reuters via a local official.

Figure 4. Waves ahead of Cyclone Chapala batter the coast of Yemen near Mukalla on Monday, November 2, 2015. Image credit: AP Photo/Mohammed Bazahier.

With Yemen plagued by civil war, it is difficult to know how extensive the damage from Chapala has been. Photos and video emerging on social media from Mukalla show major flooding, with several feet of water cascading through streets and out of the banks of a canal that runs through the heart of the city. Independent Yemen-based journalist Iona Craig reported a preliminary total of 25 injuries and 21 people missing. No fatalities have been reported thus far--an encouraging sign, although it is still very early in the process of damage assessment. “The damage is enormous,” Fahd Kafain, Yemen’s minister of fisheries, told AFP. The mountain valleys of the Hadramout region have experienced dramatic runoff from Chapala’s rains (see embedded YouTube clip below). Hadramout suffered more than 200 fatalities related to the 2008 Yemen cyclone. The impact of Chapala will undoubtedly hamper the already-difficult tasks facing humanitarian relief agencies in Yemen. Storm surge expert Hal Needham has a blog post this morning on Chapala’s landfall, including background on how topography helped tamp down the potential storm surge along the Yemen coastline.

Recent runs of the ECWMF, GFS, and UKMET models suggest that a disturbance now off the southwest coast of India could undergo tropical development in the Arabian Sea later this week, again heading toward the Arabian Peninsula. If a new cyclone were to pass directly over the same region as Chapala, it would be unlikely to attain the same strength, given the cooler waters that were stirred up by Chapala’s passage.

Figure 5. Cyclone Chapala (left) and a disturbance off the southwest coast of India, as captured by satellite at 18Z (1:00 pm EST) Wednesday, November 3, 2015. Image credit: EUMETSAT/JTWC/SATOPS.

Did climate change have anything to do with Chapala?
There is no doubt that Chapala was an extremely unusual cyclone--although we don’t know exactly how unusual, given the sketchy nature of tropical cyclone records for the Arabian Sea prior to 1990. Assuming that other factors line up favorably, then warm sea-surface temperatures boost the odds of cyclone development. In this case, Chapala formed and traveled over waters that were at record-warm levels for this time of year (see Figure 6 below). Chapala was not only the second-strongest cyclone on record for the Arabian Sea, but it was also the longest-lived at Category 3 strength. According to WU contributor Phil Klotzbach, Chapala was a major cyclone for 3.75 days, breaking the old record of 3.25 days set in 2007 by Cyclone Sidr. Due to its longevity and strength, Chapala has also generated more accumulated cyclone energy than any other Arabian Sea cyclone on record.

Figure 4. Tropical Cyclone Chapala performed its remarkable rapid intensification cycle over the warmest waters ever observed for this time of year over the Arabian Sea, as depicted in the September 2015 global climate summary from NOAA/NCEI.

Tropical cyclones are most common in the Arabian Sea in spring and autumn, during the transition periods between the strong southwest flow of the summer monsoon and the strong northeast flow that predominates in winter. A 2011 paper in Nature led by Amato Evan (University of Virginia) found that during the pre-monsoon period (spring), vertical wind shear decreased and Arabian Sea cyclones became considerably stronger in 1997-2010 as compared to 1979-1996. The authors attribute the reduced shear to a regional increase in sun-blocking air pollution, mainly black carbon and sulfates). A much more subtle decrease in strength was found for post-monsoon (autumn) cyclones in the Arabian Sea. However, the authors speculated that if emissions continued to grow, “it is plausible that very intense tropical cyclones, which have so far been limited to the pre-monsoon period, could begin to emerge in the post-monsoon season as well."

Bob Henson

Hurricane Climate Change

Chapala Closing in on Yemen; Record November Warmth in Florida, Europe

By: Bob Henson , 5:34 PM GMT on November 02, 2015

A stretch of Middle Eastern coastline unaccustomed to tropical cyclones of any type is about to experience a full-blown landfall, as Cyclone Chapala bears down on the central coast of Yemen. Chapala held its intensity remarkably well on Sunday, thanks in large part to record-warm sea-surface temperatures and light wind shear. A large, solid central core of showers and thunderstorms (convection) helped Chapala barricade itself from the influence of extremely dry air from the Arabian Peninsula. Chapala remained a Category 3 cyclone on the Saffir-Simpson scale as of 15Z (10:00 am EST) Monday, with top sustained winds estimated at 110 knots (126 mph). Cloud-top temperatures have gradually warmed across Chapala’s convective shield, and the storm has become more asymmetric in recent hours. Dry air will be infiltrating the storm more rapidly as it nears landfall, but with other conditions largely favorable, Chapala has a good chance of making landfall at Category 1 strength. Chapala swept to the north of the remote island of Socotra on Sunday night, triggering a flurry of photos and videos on social media--at least some of which were bogus, underscoring the need to double-check sources as this rare event unfolds. Al Jazeera reports that Chapala caused at least two deaths and nine injuries on Socotra, with more than 100 homes destroyed.

Figure 1. Enhanced infrared image of Cyclone Chapala, with the storm track overlaid. Icons denote Chapala’s predicted strength on the Saffir-Simpson scale. Chapala is projected to be a weakening Category 2 strength cyclone about six hours before landfall.

Figure 2. Steep hillsides surround the city of Mukalla on the central Yemen coast. Image credit: Google Images, via Stu Ostro, The Weather Channel.

Catastrophic rains possible near major Yemen city
The parched Yemen coast is nearly devoid of population centers, but Chapala is aiming for one of them. The forecast track from the Joint Typhoon Warning Center as of 10:00 am EST Monday (7:00 pm Yemen time), in close agreement with the scant model guidance available, brings Chapala into the coast about 50 miles south of Mukalla (also Al Mukallah) on Tuesday night local time, putting that city of 300,000 on the more dangerous right-hand side of the cyclone. The potential storm surge will be tempered somewhat by the steep rise of the undersea topography just offshore, but this region’s experience with any surge is very limited. According to a review paper by storm surge expert Hal Needham, there are only four observations in the scientific literature of storm surge or storm tide in the Arabian Sea. The only other hurricane-strength cyclone in modern records to affect the Arabian Peninsula is 2007’s Cyclone Gonu, which nicked the southeast corner of the peninsula en route to Iran. Water levels during Gonu reached 5 meters (16 feet) at Ras al-Hadd, Oman, although that total may include waves as well as storm surge.

Chapala’s landfall may be far enough southwest to spare Mukalla from hurricane-force winds. However, there is a far bigger threat: Chapalla’s path is virtually certain to bring torrential rain to Mukalla and the surrounding mountains, raising the spectre of potentially disastrous floods and mudslides. The counterclockwise circulation around Mukalla will pull dry air into the cyclone’s south side but will keep moist air flowing into the north side, where the heaviest rains will fall. Amount could easily top one to two feet of rain in some areas, representing a number of years’ worth of rain in this desert regime. The immediate coast averages less than 2” of rain per year.

It is difficult to overstate the rarity and gravity of this event: a hurricane-strength storm striking near a large, ancient city, situated near mountains, with no modern experience in dealing with tropical cyclones. Although Hurricane Patricia got much more media attention, Chapala may end up bringing more damage and misery by far. The ongoing civil war in Yemen can only exacerbate the suffering of those affected and complicate relief efforts. “The humanitarian situation in Yemen is deteriorating rapidly,” reported the UN Office for the Coordination of Humanitarian Affairs in an October 15 update. We can only hope that the powers that be respond to this threat in line with its seriousness.

Figure 3. 5-day rainfall totals projected by the HWRF model run for Cyclone Chapala for the period starting at 06Z (1:00 am EST) Monday, November 2, 2015. The heaviest rains--perhaps 24” to 32” or more--are projected to fall close to the city of Al Mukallah, just to the right of Chapala’s path. Image credit: NCEP/EMC.

Figure 4. Average annual rainfall in Yemen. Image credit: CIA, via Perry-Castañeda Library Map Collection, University of Texas at Austin.

The autumn heat is on in eastern U.S. and Europe
Torrential rains progressed over the weekend from Texas into the Southeast, where the western Florida Panhandle has been especially hard-hit. CoCoRaHS observations for the 24 hours ending at 7:00 am EST Monday topped 7” at one site in Walton County, and flash flood watches remained in effect at midday Monday from Florida to North Carolina.

Downstream of the heavy storms, Sunday and Monday have felt more like midsummer than mid-autumn across most of Florida. In Tallahassee, Sunday’s high temperature of 88°F and low of 75°F both tied for the warmest ever recorded there in November, and the day’s average of 81.5°F handily beat the November record of 80.5°F set on 11/11/82 (records extend back to 1892). At midnight, it was still a sultry 80°F, with a relative humidity of 87%! Tallahassee’s overnight low on Sunday night was a ridiculous 78°F, but the rains should move in later today, tamping down that reading before midnight. (Thanks to Jedkins01 for calling attention to the Tallahassee warmth.) As the front retreats north ahead of a strong upper-level trough in the West, mild, moist air will overspread most of the eastern half of the country. In parts of southern Minnesota, Wisconsin, and Michigan, nighttime lows could stay above 55°F (warmer than the average daily highs) by midweek.

Balmy temperatures are also gracing much of Europe for the first week of November, thanks to an unusually strong upper-level high. On Sunday, the United Kingdom saw its warmest November temperature in more than a century of official records, as Trawscoed, Wales, soared to 22.4°C (72.3°F), besting the previous mark of 21.7°C (71.1°F) set in the Wales town of Prestatyn on November 4, 1946. On Monday afternoon, Trawscoed warmed again to at least 21.2°C (70.0°F), based on hourly observations.

Temperatures this week will be especially mild for mid-autumn across northern latitudes and higher altitudes of Europe. Finland saw its warmest-on-record November temperature on Monday with 13.3°C (56.0°F) at the town of Jomala, which held the previous national record of 13.0°C (November 12, 1999). In Helsinki, Finland, where the all-time November record is 11.6°C (52.9°F). Helsinki’s Vantaa airport likely topped that reading on Monday, with the highest Celsius-rounded hourly observations hitting 12°C (53.6°F). The latest WU forecast calls for a high of 55°F in Helsinki on Tuesday. The town of Sunndalsøra, Norway--less than 300 miles south of the Arctic Circle--reached at least 64°F on Monday. Later this week, temperatures may inch above freezing and trigger snowmelt at altitudes as high as 4000 meters (13,100 feet) in the Alps, according to international weather records historian Maximiliano Herrera, who maintains a comprehensive list of extreme temperature records for every nation in the world on his website.

WU blogger Steve Gregory outlines the potential for continued warmth into mid-month across eastern North America, plus the latest on El Niño, in his post today.

Bob Henson

Hurricane Extreme Weather

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