Category 6â„¢

The big weather show

By: JeffMasters, 3:55 AM GMT on February 01, 2006

This week marks the largest gathering of meteorologists in the world—the annual meeting of the American Meteorological Society, in Atlanta, Georgia. The variety and depth of weather knowledge to be gained here are truly remarkable! Here are a few snapshots of what I’ve experienced so far:

What May Mayfield wants engraved on his tombstone
Max Mayfield, Director of the National Hurricane Center, addressed the conference today to talk about the incredible Hurricane Season of 2005. He noted that forecast track errors were at a record low during 2005, and that we were lucky that the major hurricanes got strong well before they hit. “One of our greatest fears is that people will go to bed at night expecting a Category 1, and wake up to an Andrew or Katrina”, he cautioned. He added: “I want it engraved on my tombstone, DON’T FOCUS ON THE CENTER BLACK LINE! Pay attention to the cone of probability when looking at hurricane forecast tracks.”


Figure 1. May Mayfield tells the American Meteorological Society audience what he wants engraved on his tombstone.

Record rains in India
Sanjiv Nair from the Department of Science and Technology in New Delhi, India, analyzed the remarkable July monsoon rainstorm that drenched parts of Bombay with more than one meter of rain in 24 hours. The rain fell from an unusual small-scale eddy in the monsoon flow that only affected a 20x20 km area. Southern portions of Bombay received only 7 cm of rain from the storm!

Hurricane Stan's effect on Guatemala
E. Hardie Sanchez-Bennett of Guatemala’s Instituto Nacional de Sismolog described the devastation wrought by Hurricane Stan in that country. Stan killed over 1500 and caused $1 billion in damage to Guatemala, a staggering toll for such a poor country. Sanchez-Bennett indicated that as a result, funding for Guatemala’s first ever weather radars—one for each coast—had been procured, and the radars would be installed within a year’s time. When I talked to him afterwards, he promised to provide the radar data to the Weather Underground when it became available.

VORTEX2
Tornado scientists Josh Wurman and Erik Rasmussen outlined VORTEX2, the most ambitious field program ever designed to study tornadoes. VORTEX2 is planned for 2008, and hopes to have a armada of 40 vehicles on the ground, including seven mobile Doppler radars. A fleet of weather research aircraft in the skies will add air support, and forays by unmanned Aerosonde aircraft—like the one that flew into Hurricane Ophelia in 2005—are planned. The study may also use a swarm of locust-sized unmanned aircraft to fly through super-cell thunderstorms.



The NOAA weather ball
Finally, the exhibit area had the coolest computer screen ever—a spherical 5-foot diameter “weather ball” that NOAA featured. The weather ball hung suspended in mid-air, and displayed a variety of animations. Included were the 2005 hurricane season, El-Nino data, weather on the sun, and a rotating Mars. It was awesome to be able to walk around all sides of the sphere and check out what was going on, on the other side of the planet!

Jeff Masters

An overestimated hurricane

By: JeffMasters, 1:18 PM GMT on January 31, 2006

Back in December, I speculated that five or six hurricanes from 2005 would get their names retired, easily besting the record of four set in 2004. Certainly, Katrina, Dennis, Emily, Wilma, and Stan will have their names retired, but what about Ophelia? The December preliminary report on Ophelia put her damage at $1.6 billion, perhaps high enough to get her name retired. Well, the National Hurricane Center has released its final report for Hurricane Ophelia, which brushed North Carolina as a Category 1 hurricane on September 14-15, 2005. It turns out that damage estimates and the estimated height of the storm surge were both considerably overestimated at the time of the storm. The Insurance Information Institute put out a preliminary estimate of $800 million in insured damage for Ophelia, which translated into a total damage estimate of $1.6 billion, based on the rough rule of thumb that total damage is double the insured damage. However, the final damage reports for Ophelia only added up to $35 million in insured damage ($70 million total damage), making it very unlikely that Ophelia will get her name retired. The $1.6 billion damage estimate was based on a model used by the insurance company. Considering that the model was off by a factor of over 20, I think we can take future preliminary damage estimates from hurricanes with a healthy dose of scepticism!

Initial storm surge heights were also considerably off, which likely let to a good part of the error in the damage estimates. If you go back to my blog from September 15, 2005, I reported: "storm surge values ranged as high as 10 - 12 feet in some of the smaller creeks in the Neuse River near New Bern, a remarkably high storm surge for what was a tropical storm for that area." This information was based on Local Hurricane Statements released by the National Weather Service at the time of the storm. I prepared a map(Fig. 1) showing the estimated storm surge from these Local Hurricane Statements. However, the NHC official storm report lists maximum storm surge height of only 4-6 feet, about half of what was reported at the time of the storm. Again, we need to be sceptical of preliminary data from hurricane landfalls.


Figure 1. Storm Surge heights measured in Ophelia.

Jeff Masters

NASA tries to silence its top climate researcher

By: JeffMasters, 2:11 AM GMT on January 30, 2006

NASA�s top climate researcher has been told by his superiors to stop voicing his opinions on climate change. Dr. James Hansen, director of the agency's Goddard Institute for Space Studies, said in a New York Times interview that the Bush administration has tried to stop him from speaking out since a Dec. 6 lecture at the annual meeting of the American Geophysical Union in San Francisco. In the talk, he gave his personal views that significant emission cuts could be achieved with existing technologies, particularly in the case of motor vehicles. Furthermore, he expressed his opinion that without United States leadership, climate change would eventually leave the earth "a different planet."

Dr. Hansen is one of the world�s foremost climate researchers. He has published hundreds of papers and testified numerous times before Congress on the issue of climate change. He said that NASA headquarters officials had ordered the public affairs staff to review his coming lectures, papers, postings on the Goddard Web site and requests for interviews from journalists. He was warned of �dire consequences� if his public statements continued. Hansen said he would ignore the restrictions, noting that NASA's mission statement includes the phrase "to understand and protect our home planet."

A public affairs official at NASA said that government scientists were free to discuss scientific issues, but that policy statements should be left to policy makers and appointed spokesmen. Since Dr. Hansen�s December 6 talk, NASA has rejected several media requests to interview him, including one by National Public Radio (NPR). According to Leslie McCarthy, a public affairs officer responsible for the NASA Goddard Institute, a NASA public affairs official appointed by the White House, George Deutsch, rejected the NPR interview request. He called NPR �the most liberal� media outlet in the country, and that his job was �to make the president look good.� Deutsch denied making the statements. McCarthy disagrees, saying she has no reason to lie.

The effort to control information coming out of NASA echoes similar directives issued last Fall in the wake of Hurricane Katrina, when on September 29, a memo aimed all National Oceanic and Atmospheric Administration employees (including those in the National Weather Service) ordered them not to speak to the national media unless the interview request was first approved by public affairs personnel. I talked to a contact at NWS who confirmed that the memo was indeed sent out, and was likely done in response to the political fallout from the Katrina disaster.

Both NASA and NOAA have emphasized that the rules preventing scientists from speaking freely to the media had always been in place, but that the rules were being enforced more rigorously now. I say the new enforced restrictions are ridiculous. Our scientists have never needed these restrictions in the past. Our tax-payer salaried scientists should be free to speak out on more than just their scientific findings without the chilling oversight of politically-appointed officials concerned with �making the president look good.� Climate change is of critical importance to all of us, and we should hear the opinions of those scientists who understand the issue the best.

Jeff Masters

Climate Change Politics Climate Change Politics

New record for the Hurricane Season of 2005

By: JeffMasters, 2:38 PM GMT on January 28, 2006

The National Hurricane Center has released its final report on Hurricane Cindy of 2005. Cindy, which had been considered a tropical storm with peak winds of 70 mph when it made landfall, is now considered a hurricane with 75 mph winds. This increases the all-time record number of hurricanes for a season in the Atlantic from 14 to 15. The previous record was 12 hurricanes, set in 1969.

Cindy followed almost the exact same track as Hurricane Katrina. Cindy made landfall in Southeast Louisiana near Grand Isle, then again on the Mississipi coast near Waveland (which doesn't exist anymore, thanks to Katrina). Detailed analysis of Doppler radar wind estimates from the New Orleans radar, plus ground-based measurements from sites not available for analysis at the time Cindy made landfall, led to the upgrade of Cindy to a hurricane. Cindy came ashore on July 5-6, 2005, and did $320 million in damage, thanks to its winds, 33 tornadoes, and 4-6 foot storm surge. Much of this damage occurred in the New Orleans area--which was only the beginning of what the Hurricane Season of 2005 had in mind for that unfortunate city. Wunderblogger squeak thought it would be intere3sting for me to mention that noticed that the surge was higher (6') on the eastern MS Coast--Jackson County--80 miles east of where landfall occured in Waveland (4' surge). according to NHC, this was because a small area of high winds to the SE of the center (the same ones that were used to identify Cindy as a hurricane for a short time) moved over Jackson County, causing the higher surge there.

I'll be back next week with my promised analysis of whether Category 4 and 5 hurricanes are increasing globally. Plus, I'll report live from the annual meeting of the American Meteorological Society in Atlanta, the world's largest gathering of meteorologists.

Jeff Masters

2005: Warmest year on record

By: JeffMasters, 6:57 PM GMT on January 25, 2006

A study released by NASA yesterday confirmed that 2005 was the warmest year on record, narrowly beating out 1998. That year a strong El Niño--a warm water event in the eastern Pacific Ocean--added significant warmth to global temperatures. The new record was set without the help of an El Ni�o. This suggests that a very substantial warming trend is affecting the globe and more "warmest years ever" will continue to occur in this decade--particularly if they are El Niño years. Global warming since the middle 1970s is now about 0.6° C (1° F ). Total warming in the past century is about 0.8° C (1.4° F). The five warmest years over the last century have occurred in the last eight years. Reliable instrument records of global temperatures extend back to about 1880, but the consensus scientific view is that the current level of warmth has been unmatched for at least the past 125,000 years.



Figure 1: (Top) Global annual surface temperature relative to 1951-1980 mean based on surface air measurements at meteorological stations and ship and satellite measurements for sea surface temperature. The blue segments represent the uncertainty of of the measurements at the 95% level. (Bottom) Temperature anomaly for 2005 calendar year. Image credit: NASA Goddard.

The plot of 2005 temperature anomalies shows that virtually all land areas across the globe were warmer than average in 2005. More warming was observed in the Northern Hemisphere than the Southern Hemisphere, and the U.S. had its 13th warmest year on record. The Arctic had the most warming, helping make the extent of summer ice coverage over the Arctic Ocean in 2005 the lowest ever measured. It's sobering to note that even the Antarctic showed a net warming for 2005. The Antarctic had been the only land area on the globe to have cooler than average temperatures the past decade. If 2005 signals an end to this Antarctic cooling trend, we can expect a higher rate of global sea level rise in coming years as Antarctic melting increases.

Jeff Masters

Climate Summaries

Caribbean disturbance no threat; winter coming back?

By: JeffMasters, 2:48 PM GMT on January 24, 2006

The tropical disturbance that formed in the western Caribbean yesterday is moving ashore over Belize, and is not a threat to become a tropical depression. Heavy rains of 4-8 inches are expected in Belize today in association with the intense thunderstorms of the disturbance. The disturbance developed in an area of low wind shear (5-10 knots) caused by a temporary split in the flow of upper-level winds over the Caribbean. This split is closing up again, and shear values are quickly rising to the very high values we are used to seeing in the tropics in winter. Computer forecast models are predicting that wind shear will remain high over the tropics the remainder of January, and no further tropical disturbances are expected this month.



Winter coming back?
The 10-14 day forecast of the GFS computer model has been consistently showing a return to a more normal wintertime pattern the past several runs. If this verifies, it means that winter will return to the eastern half of the country by the second week of February, with temperatures below normal for the first time since mid-December. The Arctic air that has numbed Russia this January is forecast to slosh across the North Pole into Canada and plunge southwards into the eastern U.S. shortly after Super Bowl Sunday--February 5. There is some doubt whether this latest forecast will verify, since the GFS model made a similar forecast back on January 10. However, the run-to-run consistency of the model is greater this time, and a "resonance" in Earth's climate system called the North Atlantic Oscillation (NAO) appears poised to switch from its positive phase to its negative phase. The negative phase is typically associated with a jet stream pattern that brings cold Arctic air to the eastern U.S., and this is the pattern seen between mid-November and mid-December, when cold air gripped much of the Eastern U.S. We have been in the positive phase of the NAO ever since, which is typically associated with very warm winter conditions across the eastern U.S.

Siberian cold hits Greece
Siberia has likely seen its coldest weather of the winter already, as temperatures have warmed considerably from the readings as low as -70 F seen last week. However, the extreme cold air from Siberia pushed into Greece today as a "back door" cold front swept in, bringing severe winter conditions to that nation. Temperatures as low as -4 F (-20 C) were recorded this morning, and high winds and heavy snows created a travel nightmare across much of Greece, Turkey, and neighboring nations. This is probably a taste of things to come for the U.S. after Super Sunday, when the Siberian Express may head our way.

Jeff Masters

Caribbean disturbance to watch

By: JeffMasters, 8:38 PM GMT on January 23, 2006

This strangest of winters has produced yet another oddity--a tropical disturbance in the Caribbean that looks very much like something one would see at the height of hurricane season. Strong westerly winds aloft--typical for this time of year--have kept the Caribbean free of tropical disturbances ever since Tropical Storm Gamma dissipated in November. However, beginning yesterday, a split in the upper level wind flow coming across Central America created an area of low shear of 5-10 knots over the western Caribbean. This morning, an intense area of deep convection developed in this low-shear area, off the coast of Belize and the Yucatan Peninsula. This disturbance does have some upper-level cirrus clouds indicating outflow to the north, but not enough organization to be worried about looking for a surface circulation. Water temperatures are 26-27 C in the western Caribbean, which is warm enough to support a tropical storm. Wind shear is expected to remain low enough through Tuesday night to allow some slow development as the system moves west or west-northwest at about 15 mph. By Wednesday, wind shear is forecast to sustantially increase, and the disturbance's motion should bring it over Belize and Mexico's Yucatan. These factors make it unlikely we'll see a tropical depression. Still, it is quite remarkable that we are even talking about a system of this nature in January!



Jeff Masters

The global hurricane season of 2005: was it unusual?

By: JeffMasters, 9:12 PM GMT on January 20, 2006

The Hurricane Season of 2005 in the Atlantic was unprecedented in its fury. Not only were records set for most tropical storms and hurricanes--2005 also saw three of the six most intense hurricanes on record. Was the rest of the globe also experiencing unusual levels of tropical cyclone activity? To answer this question, I have plotted in Table 1 the 2005 statistics, plus averages and all-time records, for the six ocean basins that experience tropical cyclones. Unfortunately, reliable records of tropical cyclone intensity in the Northwestern Pacific and Southern Hemisphere ocean basins begin in about 1987, so there is not much data available to do comparisons of how unusual the global hurricane season of 2005 was.


Table 1. Global tropical cyclone statistics for 2005 (in bold black, or green if a new record). Averages are given in parentheses. These averages are for the 1987-2004 period (18 years). All-time records are in red, and are for the entire time period data is available (1851-2004 for the Atlantic, 1949-2004 for the Northeast Pacific, and 1945-2004 for the other ocean basins).

Globally, the total number of tropical storms and hurricanes in 2005 was about 10% higher than average--97 were recorded, which is the second-most ever observed (the record is 101, observed in 1992). If one counts the Southern Hemisphere storms that occurred September through December 2004 as being part of the 2005 hurricane season, 2005 had 101 named storms, tying it for first place. Note that reliable records of total number of storms probably begin in the mid-1970s.

Besides the Atlantic, only the Southwest Pacific had an unusual 2005 hurricane season. There were five Category 4 and 5 storms in the ocean region east of Australia--which beat the old record of four storms. None of the 2005 cyclones caused loss of life or heavy damage. Category 5 Cyclone Meena merely brushed Raratonga in the Cook Islands, Category 4 Cyclone Ingrid hit a sparsely populated area of northern Australia, and the other three intense cyclones stayed out at sea. The other four ocean basins had rather ordinary seasons in 2005, with near average numbers of named storms, hurricanes, and intense hurricanes.

One rather amazing feature that stands out in 2005. For the first time on record, the Atlantic had more named storms than any other ocean basin. I thought I'd never see that happen! Atlantic storms, which usually make up just 11% of the global total, accounted for 28% of the global total in 2005. So while nature did indeed go berserk during the Atlantic Hurricane Season of 2005, the rest of the oceans did not, fortunately.

Next week: A 2005 paper in Science magazine presented evidence that the global number of Category 4 and 5 hurricane is increasing, due to global warming. Dr. Bill Gray of Colorado State has posted a critique of the findings, and claims there is no evidence that the global number of Category 4 and 5 hurricane is increasing. I'll present an in-depth analysis of the arguments pro and con.

Jeff Masters

Wacky winter warmth--no end in sight

By: JeffMasters, 3:29 PM GMT on January 18, 2006

The bizarre winter of 2005-2006 continues unabated this week, with record warm temperatures continuing across North America. Drought continues to plague many areas across the southern half of the U.S., and the hoped-for rains across Texas, Oklahoma, and Arkansas this week have mostly failed to materialize. January temperatures have ranged from 5 to 20 degrees above normal across most of the U.S. and Canada, and Canada's usual plentiful supply of Arctic air is absent. There are no signs that winter will return to North America anytime soon--the long range forecast from the GFS model continues to show far above-normal temperatures persisting into the first week of February. With the emergence of a full-fleged La Nina episode this month (see my previous blog), we should expect the jet stream to maintain a more northerly position, which will continue to keep this winter unusually warm.

How strange is this winter's warmth? Duluth, Minnesota, whose average low temperature is 0 F in January, has not recorded a low temperature below 3 F this month. The record fewest January days Duluth has had a sub-zero temperature is three days (1898). I wouldn't be at all surprised if Duluth winds up with no sub-zero temperatures this month.

Is all this due to global warming? Well, one cannot blame a single weather event--or single anomolous season--on global warming. However, the continued warming of the globe makes warmer winters more likely, as well as strange weather patterns that we're not used to seeing. The climate is changing, and we should expect to see unusual weather patterns increase in the coming years. Preliminary figures indicate that globally, 2005 was the warmest or second warmest year on record. This is pretty remarkable, since 2005 wasn't even an El Nino year. Previous record warm years have all been El Nino years, due to the extra heat these events add to the globe.

But it is really cold in Siberia!
Siberia, and indeed all of Russia and Asia, are experiencing one of their coldest winters on record. As is often the case when one part of the globe is experiencing record warmth, the jet stream is kinked in a way that funnels exceptional cold air to another region of the globe. The high temperature in Curapca, Siberia today was -58 F. The temperature hasn't risen above -26 F this year, and the low temperature has hit -64 F four times this January. This reading is still a ways away from matching the coldest temperature ever measured in the Northern Hemisphere--the astounding -67.8 C (-90 F) set at Siberia's notorious Pole of Cold in 1885. I doubt this winter's cold in Siberia will approach that record.

Still, in the Novosibirsk region of Siberia, temperatures fell to minus 40 degrees Fahrenheit--the lowest in 100 years. In the city of Krasnoyarsk, celebrations for the Russian holiday known as Old New Year's Eve were canceled Friday after temperatures were also predicted to fall to minus 40. I'm sure the talk of the threat of global warming is at low ebb across Russia this winter, as the cold has caused unusual hardship.

Jeff Masters

Winter Weather

La Niña is here

By: JeffMasters, 4:34 PM GMT on January 16, 2006

La Niña is back. In their January 12 dicussion, NOAA's Climate Prediction Center declared that the cooler waters and increased easterly winds off of the western coast of South America that have developed the past two months have met the official criteria to be called a weak La Niña event. As seen in Figure 1 below, sea surface temperatures along the equator between the South American coast and the Date Line (180 degrees longitude) are about .5 C cooler than normal, which is the threshold for a La Niña event. The last La Niña occurred in 2000-2001 and was a weak event.



La Niña events can have a strong effect on the climate across the Pacifc, North and South America, and the Atlantic. In particular, La Niña winters see a more northerly jet stream over the U.S., which leads to drier weather over southern half of the country. Major droughts have accompanied two recent major La Niñas in the Midwest (1988-89) and Southern Plains (1995-96). The Pacific Northwest tends to be wetter and colder during La Niña. The Northeastern U.S. sees little change in precipitation and slightly increased maximum temperatures. Tornado and severe storm activity tends to shift more to the north in Spring due to the more northerly location of the jet stream.

Up until 1975, La Niña events and El Niño events used to alternate fairly regularly with a period of 2-7 years. Between 1950 and 1976 there were seven El Niño events and seven La Niña events. Since 1976, El Niño events have been approximately twice as frequent as La Niña events, with ten El Niño events and only six La Niñas. Some researchers have speculated that this is due to the effects of global warming causing a new "resonance" in the climate system. If so, this is one way in which global warming may end up causing a decrease in Atlantic hurricane activity over the coming decades, since the increased wind shear over the Atlantic during EL Niño events greatly reduces the number and intensity of these storms.

Effect of La Niña on hurricane season
It is well known that La Niña conditions enhance tropical storm formation in the Atlantic. The winds associated with La Niña tend to decrease the amount of wind shear in the tropical Atlantic, allowing more storms to form, and more major hurricane to occur. During La Niña more hurricanes form in the deep Tropics from African easterly waves, and these systems have a much greater likelihood of becoming major hurricanes that threaten the U.S. and Caribbean islands. However, the current La Niña is a weak one, and about 80% of the computer models used to forecast La Niña predict that it will no longer be around this Fall. Neutral El Niño/La Niña are expected for the coming hurricane season--which is what we had during the record-breaking Hurricane Season of 2005.

Jeff Masters

Drought relief?

By: JeffMasters, 3:04 PM GMT on January 12, 2006

Computer forecast models are pointing to a change in the jet stream pattern over the coming week that could provide some drought relief to the southern half of the U.S., including eastern Texas, Oklahoma, and Arkansas. The jet stream so far in January has been blowing in a somewhat "zonal" fashion--straight across the U.S., from about Oregon to New England. The jet has had only modest dips to the south (troughs), associated with rain storms that have tracked rapidly across the northern tier of states. Beginning Saturday, however, the jet stream is expected to take on a more bowed pattern, bringing a sharp trough of low pressure all the way down to Mexico. This trough will bring cold air and moisture with it, giving southern California needed rains, and the first snows of winter to Flagstaff, AZ. Amazingly, Flagstaff had over 83 inches of snow fall by this time last year, but so far this winter has had none!

By Monday, as the trough moves across the country, the drought-ravaged areas of eastern Texas, Oklahoma, and Arkansas have a chance of up to .5 inches of rain. This would be the first significant rains in nearly 100 days in some areas. Another major trough is expected to follow about a week later, and indications are that this trough will also swing far enough south to bring rain and snow to portions of the southern U.S. in need of moisture. However, since there is no cold Arctic air in Canada for these troughs to tap into, only short periods of winter-like conditions are expected in the U.S. over the next ten days. The country remains on track to record our warmest-ever January.


Figure 1. Number of days since the last .25 inch rain for each county in Oklahoma.

Jeff Masters

Drought

No Alberto--and where's winter?

By: JeffMasters, 3:38 PM GMT on January 11, 2006

No Alberto
A large non-tropical low pressure system is about 500 miles off of the Atlantic coast of Africa, and is located about midway between the Canary and Cape Verde Islands. This low has weakened in the past day, and has developed only a small amount of deep convection, mostly east of the center. The low is forecast to slow drift southward and continue to weaken, and very high levels of wind shear are expected to move over the low by Friday. Thus, it appears very unlikely that this low will develop into Tropical Storm Alberto. Forecast models show no other tropical storm threats developing over the next week, as high wind shear dominates the Atlantic basin.

Where's winter?
Those of us living in the eastern 2/3 of North America are wondering--where's winter? After unusually early and severe winter weather gripped the region from late November through mid-December, a very warm weather pattern has brought delight to those of us dreading high natural gas bills this winter--but despair to the skiiers. There is cold air out there this winter--but it's in Asia, and not headed our way anytime soon.

New Delhi, India saw its coldest winter morning in 70 years on Sunday as the temperature plummeted to 0.2 degrees Celsius (32.4 Fahrenheit). Pakistan and the hard-hit quake areas of Kashmir are experiencing their coldest winter in a decade, and China Daily calls the current winter in China the coldest in 20 years. In Japan, a month of heavy storms has piled snow up to three meters high in some areas, and at least 63 people have died and over 1,000 have been injured because of the snow. Many of the dead were elderly people who fell from their roofs while trying to clear snow, while others were crushed when their houses collapsed under the snow's weight.

When is this pattern going to break? According the the GFS model, no major shifts in the winter pattern are expected in the next two weeks. Asia will stay cold. A succession of rain storms will move across the northern half of the U.S. the remainder of January, with only a brief day or two of cold air moving in behind these storms. Eastern North America may have to wait until February before more normal winter weather returns and Asia gets a break.

Jeff Masters

Global warming and hurricanes part 2: An increase in late-season activity?

By: JeffMasters, 6:33 PM GMT on January 09, 2006

Good Tuesday to everyone! This week we need to watch a large extratropical low-pressure system sliding down the coast of Africa towards the Cape Verde Islands. This low is similar to the storms that spawned Delta, Epsilon, and Zeta, and has the potential to slowly gain tropical characteristics and become Tropical Storm Alberto later this week. However, it appears that wind shear levels will probably be too high and the water too cool for a new tropical storm to form. The chances of a tropical storm forming this week are probably around 20%.

Has there been an increase in late-season tropical storm activity?
Hurricane experts agree that global warming has not led to an increase in the number of tropical cyclones occurring world-wide, and are currently debating whether or not global warming has affected tropical cyclone intensity (more on this later in January, I've been pulling together a lot of material). Is global warming possibly affecting the length of hurricane season, as well? It seems that an inordinate number of late-season and off-season tropical storms have been forming in the Atlantic the past few years. For example, two December storms formed in 2003, which also had the first-ever April storm, Tropical Storm Ana. Cuba's worst hurricane ever, Hurricane Michelle, hit in November 2001, and the Atlantic's second deadliest hurricane of all time, Hurricane Mitch, lasted into November 1998. Add to this 2005's Greek cousins, Gamma, Delta, Epsilon, and Zeta, which all occurred in November and December. To see if hurricane season is indeed lasting longer, I plotted up the number of days a named storm existed each year from November through April (Figure 1). The data cut-off is 1944--the beginning of reliable hurricane records in the Atlantic, thanks to regular long-range aircraft reconnaissance missions. According to Dr. Chris Landsea's paper, A Climatology of Intense Atlantic Hurricanes, only a very few short-lived tropical storms that formed far out over the open Atlantic were missed by these aircraft missions or ships plying the shipping lanes between Europe and North America. For example, all of 2005's Greek storms were long-lived enough and sufficiently intense that they would have been detected back in the 1944-1960 time frame. Beginning 1960, weather satellites gave us full coverage of all the ocean areas, and it is unlikely we missed any tropical storms after then. Thus, Figure 1 is likely to be an accurate measure of the late-season tropical storm activity for the Atlantic.


Figure 1.Number of days a named tropical storm was present in the Atlantic for each year during November through April, 1944-2005. The 2.5 named tropical storm days from the March 2004 hurricane in the South Atlantic that hit Brazil--Hurricane Catarina--are not included.

Looking at Figure 1, we see a noticeable increase in the number of late-season named-storm days in the Atlantic in the past decade, roughly coinciding with the upswing in Atlantic intense hurricane activity that began in 1995. This increase in late-season tropical cyclone activity was not observed during the previous warm phase of theAtlantic Multidecadal Oscillation (AMO), the natural cycle that greatly influences hurricane activity in the Atlantic. This previous warm phase of the AMO lasted from 1926-1969. Thus, it seems unlikely that the recent upswing in late-season Atlantic tropical storm activity is due to the AMO. Is global warming to blame, then? Global sea surface temperatures in the tropics have increased by .3 degrees C (.5 degrees F) the past century, so it is reasonable to ask if this increase has lengthened hurricane season.

To answer this question, we look at the November though April number of tropical storm days for the Northern Hemisphere's other ocean basins that have tropical cyclones--the Western Pacific (Figure 2) and the Eastern Pacific (Figure 3). Neither ocean basin shows any increase in the length of their hurricane seasons, so global warming has not caused a Northern Hemisphere-wide increase in the length of hurricane seasons. If global warming is to blame for the recent increase in Atlantic late season and off-season tropical storm activity, it is probably through some as yet not understood mechanism, and not directly due to increased the sea surface temperatures over the Atlantic.


Figure 2. Number of days a named tropical storm was present in the Northern Hemisphere's Western Pacific Ocean for each year during November through April, 1945-2005.


Figure 3. Number of days a named tropical storm was present in the Northern Hemisphere's Eastern Pacific Ocean (off the coast of Mexico) for each year during November through April, 1949-2005

Jeff Masters

Climate Change

The Hurricane Season of 2005 finally ends!

By: JeffMasters, 9:51 PM GMT on January 06, 2006

Tropical Storm Zeta has finally disintegrated into a remnant low, and the National Hurricane Center has issued its last advisory for the Hurricane Season of 2005. In the words of NHC forecaster Stacy Stewart in the final discussion on Zeta:

I suppose it is only fitting that the record-breaking 2005 Atlantic hurricane season ends with a record breaking storm. Today, Zeta surpassed 1954 Alice #2 as the longest-lived tropical cyclone to form in December and cross over into the next year. Zeta was also the longest-lived January tropical cyclone. In addition, Zeta resulted in the 2005 season having the largest accumulated cyclone energy (ACE) surpassing the 1950 season. So, until the 2006 season begins...unless Zeta somehow makes an unlikely miracle comeback...this is the National Hurricane Center signing off for 2005...finally.

Re-writing the record book for Atlantic hurricanes
The official NHC final report for Hurricane Epsilon is out, and says:

"Epsilon, the record-setting 26th and final named tropical cyclone of the 2005 hurricane season..."

So, we'll have to re-write the record books for the Hurricane Season of 2005, as well as the entire historical record book for Atlantic hurricanes. I'm guessing Dr. Franklin felt a tad uneasy when he penned that line on December 16. I know I felt a little uneasy when I wrote my "final" blog on the Hurricane Season of 2005 after Epsilon finally dissipated. Is there a Tropical Storm Zeta lurking in the future, I wondered? Maybe so...

So let's close the books on the Hurricane Season of 2005, and hope we never see anything like it in our lifetimes. I do believe that this was a once-in-a-lifetime hurricane season. Even if it turns out that global warming proves to have a dramatic impact on Atlantic hurricanes in the coming decades, I seriously doubt I'll live to see another season with 27 named storms, or a season with three of the six most intense hurricanes of all time.

I posted a revised list of the records set during the Hurricane Season of 2005; if I've made any major omissions or errors, let me know!

Coming next week: Late-season Atlantic tropical cyclones: has there been an increase in recent years?

Jeff Masters

Re-writing the record books for Atlantic hurricanes

By: JeffMasters, 5:46 PM GMT on January 06, 2006

The official NHC final report for Hurricane Epsilon is out, and says:

"Epsilon, the record-setting 26th and final named tropical cyclone of the 2005 hurricane season..."

So, we'll have to re-write the record books for the Hurricane Season of 2005. I'm guessing Dr. Franklin felt a tad uneasy when he penned that line on December 16. I know I felt a little uneasy when I wrote my "final" blog on the Hurricane Season of 2005 after Epsilon finally dissipated. Was there a Tropical Storm Zeta lurking in the future?
Surely not!

Well, we have one more record to add our incredible tally of records--the latest ending hurricane season of all time. Zeta has lasted until January 6, beating out the January 5 ending date of the 1954 hurricane season. The Hurricane Season of 2005 is not officially over--but will be tonight. High wind shear and dry air have contributed to the extensive deterioration of Zeta today, and this afternoon's advisory should be the last one for the Hurricane Season of 2005. Zeta is now just a swirl of low clouds, and has no deep convection anywhere near it. With dry air and high wind shear expected to continue for the next two days, the chances of regeneration are slim. So let's close the books on the Hurricane Season of 2005, and hope we never see anything like it in our lifetimes. I do believe that this was a once-in-a-lifetime hurricane season. Even if it turns out that global warming proves to have a dramatic impact on Atlantic hurricanes in the coming decades, I seriously doubt I'll live to see another season with 27 named storms, or a season with three of the six most intense hurricanes of all time.

Coming next week: Late-season Atlantic tropical cyclones: has there been an increase in recent years?

Jeff Masters

Zeta (again!), and the Texas drought

By: JeffMasters, 4:06 PM GMT on January 05, 2006

I was hoping to be able to declare an end to the Hurricane Season of 2005 today, but Zeta had other ideas. After weakening to a tropical depression last night, Zeta has made another comeback and is a tropical storm again. Satellite imagery is showing deep convection moving in towards Zeta's center on the east side, and both ship reports and satellite measurements support calling Zeta a tropical storm once again. The wind shear has apparently dropped this morning, allowing the re-organization. This is likely to be short-lived, and extremely high levels of wind shear are forecast to impact the storm tonight. This shear will surely tear Zeta apart by Saturday at the latest.

The Texas/Oklahoma drought
The latest drought map for the U.S. was released today, as it is every Thursday by the NOAA Climate Prediction Center. Comparing today's image to the one from a month ago shows the steady increase in area and severity of the drought affecting Texas, Oklahoma, Arkansas, and surrounding areas. Today's drought map now puts the Dallas/Fort Worth metro area into the "exceptional" drought category, the most severe category of drought. Ninety-day rainfall totaled less than half normal across the southern Mississippi Valley, resulting in "severe" drought expanding into northeastern Arkansas and southwestern Missouri, while the "extreme" drought in southern Texas joined the extreme drought area in the north. Twelve-month rainfall deficits exceed 20 inches in southeast Oklahoma, northeast Texas, southwest Arkansas, and parts of Louisiana. It's ironic to note that had Hurricane Rita hit Houston and moved northward across Dallas/Fort Worth as originally forecast, her 4-8 inch rains would have likely saved tens of millions of dollars in drought damage the area is seeing now. Of course, Rita would have done billions in other damage, so I'm sure given the choice, the drought-stricken areas will take the drought!

Easing of the Northwestern U.S. drought
Figure 1 also shows a marked easing of the drought affecting the Northwest U.S., where most areas have been under a significant 5-7 year drought. While just one season of rains cannot put enough groundwater back into the aquifers to fully break such a long term drought, conditions this winter are a fantastic turn around for an area that was under extreme to exceptional drought for years.


Figure 1. Drought maps for December 6 and January 3, showing the progression of the drought over Texas, and the relaxing of the drought over the Northwestern U.S.

Jeff Masters

Drought

Zeta dying; Texas drought thriving

By: JeffMasters, 6:24 PM GMT on January 04, 2006

Tropical Storm Zeta is falling apart. Wind shear analysis from the University of Wisconsin shows 30 - 50 knots of shear over Zeta, and this shear has blown away nearly all the storm's deep convection. Zeta is a swirl of low clouds with just a few thunderstorms on the east and northeast side. With wind shear expected to remain high, Zeta will likely be dead within 24 hours. But before you believe this forecast, you might want to review some of the comments about Zeta in the official National Hurricane Center discussions the past few days:

10 PM EST SUN JAN 01 2006
I HAVE NO CHOICE BUT TO FORECAST WEAKENING AGAIN AND AGAIN.

4 PM EST MON JAN 02 2006
THEREFORE I HAVE NOT BACKED OFF ON THE FORECAST OF WEAKENING. OF COURSE...ZETA MAY HAVE OTHER IDEAS.

4 PM EST TUE JAN 03 2006
SO...ALTHOUGH YOU'VE HEARD THIS FROM US BEFORE...WE EXPECT A WEAKENING TREND TO COMMENCE TOMORROW.

10 AM EST WED JAN 04 2006
AS YOU CAN SEE...I RAN OUT THINGS TO SAY.

Long-term tropical storm outlook for January
Today's model runs are still forecasting that a non-tropical low pressure system will form off the coast of Africa on Sunday, in a location similar to but farther east of where Delta, Epsilon, and Zeta all formed. This new low could make the transition to a tropical storm early next week. However, the latest model runs have the storm forming closer to the coast of Africa than before, and the cooler water temperatures there will probably keep it from forming into a tropical storm.

The Texas/Oklahoma drought
Wildfires aided by record high temperatures, low humidities, high winds, and persistent drought conditions continue to ravage Texas, Oklahoma, and New Mexico. With no significant rains expected for at least a week, conditions will not improve in the forseeable future. Some of the record highs observed yesterday:

January 3 record highs:
-----------------------
Austin, TX 86
Abilene, TX 86
Del Rio, TX 86
San Antonio, TX 86
Wichita Falls, TX 85
Dallas, TX 84
Lubbock, TX 83
Midland, TX 83


Figure 1. Drought map for the U.S., released December 28. Severe drought conditions began over the Texas/Oklahoma area in April 2005, and have steadily worsened.

A cold front moving through the area today will bring an end to the record heat for at least a week, but strong winds--typical for this time of year--are expected to move in periodically during the week and fan any fires that may start. The jet stream is expected to stay well north of the area for the next 10 days, keeping any rain-producing storms to the north. The GFS model is suggesting that by January 18, this pattern may break down, allowing rains to return. However, a 2-week forecast is a bit of a stretch, and it would be no surprise if the more northerly jet stream pattern stays entrenched for the rest of January.

Drought and hurricane activity
Some researchers have suggested that upswings in hurricane activity like the one we've seen in the past ten years tend to be associated with more frequent drought conditions across the Western and Midwestern U.S. This was the case during the 1930s, when a period of very high hurricane activity coincided with the famed Dust Bowl drought that affected the Midwestern U.S. Much of the Western U.S. has suffered severe drought conditions for the past 5-7 years, coinciding with the recent upswing in Atlantic hurricane activity.

Jeff Masters

Drought

Hurricane Zeta?

By: JeffMasters, 6:27 PM GMT on January 03, 2006

The Hurricane Season of 2005 refuses to quit. Tropical Storm Zeta has not changed much since yesterday, but the forecast for its future has changed considerably. Zeta may become a hurricane by tomorrow. The upper-level trough approaching Zeta is splitting in two, leaving a area of low wind shear just in front of the storm. Wind shear analysis from the University of Wisconsin shows that Zeta's westward motion is carrying the storm into an area of low wind shear less than 10 knots, and this reduced wind shear has the potential to allow Zeta to intensify into a hurricane, something the GFDL model has been consistently predicting for three days.

The reduced wind shear also means that Zeta will hang around much longer than previously thought. A trough of low pressure just to Zeta's west is expected to turn the storm northwards tomorrow, but this trough will probably not be strong enough to completely recurve the storm. Zeta will have to wait for the next trough late in the week before finally recurving and dissipating. During that period, Zeta may reach hurricane intensity for a day or so before increasing shear knocks it back down to a tropical storm.

Long-term tropical storm outlook for January
Today's model runs are now suggesting that a non-tropical low pressure system will form off the coast of Africa on Sunday, in a location similar but a little farther east of where Delta, Epsilon, and Zeta all formed. It is possible that this low could make the transition to a tropical storm early next week. However, the cooler water temperatures in this low's more easterly location will probably keep it from forming into a tropical storm.


Figure 1. Tropical Storm Zeta as seen by the polar-orbiting Terra satellite. Image courtesy of the Navy Research Lab.

Tomorrow: More on Zeta, and the Texas/Oklahoma drought.

Jeff Masters

Zeta looking strong

By: JeffMasters, 6:50 PM GMT on January 02, 2006

Tropical Storm Zeta is making a comeback this afternoon, with deep convection blossoming and starting to wrap all the way around the center. Wind shear analysis from the University of Wisconsin shows that Zeta's westward motion is carrying the storm into an area of lower wind shear of about 20 knots, and this reduced wind shear is likely contributing the the storm's improving appearance. The lower shear will be short lived, however, and higher shear values of about 40 knots should impact the storm by Tuesday and significantly weaken or destroy Zeta. There is a small chance it might attain hurricane strength before the higher shear weakens the storm.

Long-term tropical storm outlook for January
OK, I can't believe I have to do this, but here comes the long-term tropical storm outlook for January. There are no other suspect areas to watch in the tropics for the next ten days, and wind shear levels are forecast to be too high to allow tropical storm formation. Historically, only one tropical storm has formed in January, an unnamed 1978 subtropical storm that formed near where Zeta is now. February, March, and April all have each had one tropical storm form since record keeping began in 1851. It would be no surprise if 2006 had a winter tropical storm form, given the ways things have gone of late. However, the chances of this happening are probably less than 20%, and I am forecasting that after Zeta, we're off the hook until early June.

Jeff Masters

Welcome to the hurricane season of 2006!

By: JeffMasters, 9:33 PM GMT on January 01, 2006

Happy New Year, everyone, and welcome the hurricane season of 2006! Last year's hurricane season went from A to Z--Arlene to Zeta--but this year's hurricane season will be the first to go from Z to A, at least at the start. We start the hurricane season of 2006 with Tropical Storm Zeta, and the next storm of the year will be called Alberto. If 2006 is like 1914, that will be all--hurricane season will end after just one storm, and the season will truly go from Z to A. Another, more likely way for the season to go from Z to A, is for the season to pass all the way through the alphabet again, recyling the Greek name Alpha by the end of the year.

Zeta has been holding on against persistent wind shear today, and appears likely to hang around at least another day or two as it slowly drifts westward over the open Atlantic. By Wednesday, if Zeta is still around, a strong trough of low pressure moving off of the U.S. coast should be able to recurve Zeta to the north and destroy the storm.

Jeff Masters


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

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About

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