Category 6™

Huge Arctic ice shelf breaks away

By: JeffMasters, 12:28 AM GMT on December 31, 2006

A huge ice shelf 25% larger than the island of Manhattan broke off of Canada's Arctic coast in 2005, according to a press release issued Thursday by researchers at the University of Ottawa's Laboratory for Cryospheric Research. The Ayles Ice Shelf, located on the northern coast of Ellesmere Island, was about 66 square kilometers in area and 100 feet thick. The ice shelf has drifted about 50 km, and is now a big iceberg about 800 km south of the North Pole. It is expected to slowly melt over the next few years and drift into the Beaufort Sea, where it may pose a threat to shipping and oil and gas developments. Melt water from the giant new iceberg will not contribute significantly to sea level rise, since it was already floating on the ocean surface (think how ice cubes floating in a cup of water do not raise the level of the water after they melt). A slight sea level rise will occur, because the melting fresh water will displace denser salty ocean water. The addition of the ice shelf's fresh water to the Arctic Ocean will not freshen the ocean detectably, since the ice shelf will melt slowly and is a relatively small chunk of ice in a huge ocean.

Figure 1. October 21, 2003 image of the northern coast of Canada's Ellesmere Island, showing the location of the Ward Hunt Ice Sheet, which broke up in 200-2003, and the Ayles Ice Sheet, which broke away in August 2005. Image credit: NASA.

Figure 2. NASA Modis satellite image from August 13, 2005, showing the Ayles Ice Shelf detaching from Ellesmere Island.

The Ayles Ice Shelf actually broke off on August 13, 2005, and created tremors strong enough to be detected by seismographs 250 km away. The break off was not announced until researchers had time to study the event. The ice shelf was one of six large ice shelves remaining in the Canadian Arctic. The region's largest ice shelf, the Ward Hunt Ice Shelf, broke up in 2000-2003. In both cases, the warming of the average air temperature by 1.8 �C in the past 40 years is thought to be the cause. Unusually warm temperatures in 2005 proved to be the final blow to the ice sheet. The hot summer of 2005 led to the greatest loss of Arctic ice ever observed--about a 20% decrease over the levels observed in 1979, when reliable record keeping began. The ice shelves along the northern coast of Ellesmere Island have thinned 90% since they were discovered in 1906 by polar explorer Robert Peary.

While much of the past warming of the Arctic can be attributed to natural causes, a significant and growing portion of the warming is thought to be due to human-caused climate change, according to the Arctic Climate Impact Assessment (ACIA), a 2004 study compiled by 300 expert Arctic scientists. Considering that radiocarbon dating of driftwood on the Ayles Ice Shelf puts its age at 3,000 years old, I think it is very unlikely that the shelf would have collapsed without the aid of warming from greenhouse gases emitted by humans. The Arctic is expected to warm another 2-4 �C by the end of the century, which should permanently destroy all the remaining ice shelves in the Arctic. These ice shelves hold a rare and unique ecosystem of cold-adapted organisms, and their loss will mean something irreplaceable and fascinating will be forever lost.

I'll have much more to say on what's going on in the Arctic in early 2007. Have a Happy New Year, everyone! My resolution will be to appreciate all that I have, and all the beauty and diversity the world has to offer. Much that is unique and beautiful on Earth will be lost to future generations. It's up to us to appreciate these things now--and work to save what we can, without crippling civilization in the process.

Jeff Masters

Climate Change

Dreaming of a brown Christmas

By: JeffMasters, 1:04 AM GMT on December 28, 2006

It's the year of the brown Christmas. The lack of snow across the entire Northern Hemisphere has been remarkable both in its areal coverage and depth, thanks to December temperatures 5-20 degrees F above normal. In the U.S., most of the eastern 2/3 of the country was snow free on Christmas (Figure 1). Granted, Colorado had a white Christmas and the mountains of Washington got slammed with snow this year, but places like northern Maine and Michigan's Upper Peninsula--which normally (Figure 2) have over two feet of snow on the ground this time of year--were snow-free. Munising, Michigan had it's first brown Christmas since 1911, and Minneapolis, Minnesota--which normally receives over 18 inches of snow by this time of year--has had a paltry one inch of snow so far this winter.

Figure 1. The U.S. white Christmas map. Image credit: NOAA.

Figure 2. The departure from normal of snow depth on Christmas day 2006. Note the large areas of orange across northern New England and northern Michigan where snow depths are over 2 feet below normal.

Hitler and Napoleon missed their chance
The warmth and lack of snow are also affecting all of Europe. The famed Russian winter that stopped the armies of Hitler and Napoleon has failed to show up this year. Virtually all of Europe has seen the warmest and least snowy December on record, to go with their warmest fall on record. Temperatures in Moscow this December have hit 47 F, a full 87 degrees above the lowest readings recorded last winter. The brown bears at the Moscow zoo have refused to hibernate for the first time ever, thanks to the record warmth.

Normally, an unusually warm winter in one part of the Northern Hemisphere means that another region is receiving an unusually cold winter. A persistent kink in the jet stream pattern typically sets up in these cases, pumping cold air from the pole down to one region, and warm subtropical air northwards into an adjacent region. However, that is not the case this year. Land areas in huge areas of the Northern Hemisphere, including most of Asia (Figure 4), have temperatures well above normal. This is something I've never seen before--there's almost no cold Arctic air to be found. Note, however, that the unusual warmth does not extend to the Southern Hemisphere; December has been colder than normal across much of Africa, South America, and Australia. Melbourne, Australia had its coldest Christmas Day on record with the temperature peaking at 14.5C. The previous lowest recorded temperature was 15.9C, in 1935.

Figure 3. Northern Hemisphere snow cover on Christmas Day 2006. Note the complete lack of snow over Europe, except in northern Scandinavia. Image credit: NOAA.

Figure 4. Northern Hemisphere departure of temperature from normal (in Centigrade) for Dec 1 - Dec 25 2006. Note that almost all the land areas of North America, Europe, and Asia were well above normal.

Will it stay warm?
When my nephew Cody eagerly unwrapped his new snow board this Christmas and asked me when he might get a chance to use it, I told him, "What are you thinking? This is Michigan in the 21st century! There's not going to be any more snow." I exaggerate slightly, but I don't recommend that anyone invest in the winter sports equipment industry this year. The latest 2-week forecast from the GFS model shows no end in sight for the warm conditions in North America. I'm guessing that our next outbreak of cold Arctic air in the U.S. won't come until mid-January. According to the International Research Institute for Climate and Society at Columbia University (IRI), January through March should be warmer than average across virtually the entire globe.

The unusual warmth this winter probably has four main causes. Firstly, this is an El Nino year, and it is common for portions of the Northern Hemisphere to experience warmer than average conditions during these events. Add to this the warming due to the observed global warming trend of 1 degree F over the past century, and the usual natural variability due to such phenomena as the North Atlantic Oscillation. Now, let's talk about sea ice in the Arctic. The Arctic Ice Cap has shrunk by about 20% since 1979, and at the end of November this year, the amount of sea ice in the Arctic was about 2 million square kilometers less than had even been seen in any previous November. December has also seen the lowest sea ice coverage for any December on record. All this exposed water provides a huge source of heat and moisture in the Arctic that retards the formation of the usual cold air masses over the adjacent regions of Canada and Siberia. It's impossible to know how much of an effect this has without doing some detailed model studies, but I think the record low sea ice in the Arctic is probably a significant contributor to this winter's record warmth. The Arctic Ice Cap is expected to continue to decline, due to human-caused global warming, according to the 2004 study by 300 scientists, the Arctic Climate Impact Assessment (ACIA). Many of us who are used to the reality of a white Christmas will find it only a dream in the coming years. I expect that the unnaturally warm winters we've experienced the past two years in the U.S. will become the norm ten years from now--and may already be the new norm.

Figure 5. Northern Hemisphere sea ice area departure from normal for Novembers from 1979 to 2006. Image credit: National Snow and Ice Data Center.

Jeff Masters

Climate Change

The hurricane shrine of Key West

By: JeffMasters, 10:47 PM GMT on December 22, 2006

The long Christmas weekend is upon us, and I thought it would be fitting to write about my visit a few weeks ago to the Key West's Hurricane Grotto--the Our Lady of Lourdes Shrine at St. Mary's Star of the Sea Roman Catholic Church at 700 Truman Avenue. It was there in 1922 that Sister M. Louis Gabriel and her fellow nuns created a stone shrine in memory of the 600 who died during the great Atlantic-Gulf hurricane of Sept. 10, 1919, a Category 4 hurricane that made a direct hit on Key West. Sister Gabriel blessed the grotto and vowed, "As long as the Grotto stands, Key West will never experience the full brunt of a hurricane." Key West residents regularly make pilgrimages to the grotto to light candles and pray for protection from hurricanes. So far, the grotto has worked--no Key West resident has died from a hurricane strike since the 1919 hurricane. However, as Brian Norcross pointed out to me, the Grotto's protection has not been perfect. Key West did suffer the brunt of Hurricane Georges in 1998, which made a direct hit on the island as a Category 2 storm with 105 mph winds. Key West also felt the western eyewall of a Category 3 hurricane in September 1948. The hurricane's calm eye passed over Boca Chica Key 8 miles to the east of Key West, bringing winds that were clocked at 122 mph at Boca Chica Airport before the anemometer blew away.

I was eager to see the famed Grotto myself and offer my own thanks for a merciful 2006 hurricane season. After a short walk from the hubbub of downtown Key West's gift shops and restaurants, I found myself on the church grounds where the grotto stands, surrounded by majestic trees and bordered by inviting paths and gardens. As I neared the stone edifice, my footsteps slowed automatically, for here was clearly a place that should be approached slowly and with reverence. I could feel a powerful spiritual energy emanating from the Grotto. It was clear that many, many people had prayed here in the 85 years since its construction. I entered a small cave filled with burning candles, and stood in quietness before the altar, offering my prayers of thanks for a quiet 2006 hurricane season, and add my own wishes for Key West's continued protection.

Figure 1. Key West's famous Hurricane Grotto.

Has the lack a direct strike by a hurricane in Key West since 1919 been unusual? Yes. South Florida is the most hurricane prone area in the Atlantic next to Puerto Rico, so it is surprising that we've gone so long without a bad hurricane in Key West. Hurricane Wilma brought a 5-foot storm surge to Key West in 2005 and caused millions in damage, but the brunt of the hurricane missed the island. Likewise, when Hurricane Rita approached Key West in September of 2005, it was apparent that the protection of the Grotto would be severely tested. But as I wrote in a blog the day after Rita passed:

Well, the protection of the grotto worked again. Key West barely escaped the brunt of a severe hurricane that could have been so very much worse. Had Rita's intensification cycle started 24 hours earlier, and she tracked 50 miles further north, the city of Key West would have been devastated. The Key West airport never measured sustained hurricane force winds from Rita, although the National Hurricane Center did receive an unofficial report of sustained winds of 75 mph with gusts to 102 mph in the Key West area. There was flooding and wind damage that will no doubt add up to tens of millions of dollars, but Key West is feeling lucky tonight. Key Westers, pay a visit to your grotto tomorrow and give thanks!

This holiday season, give thanks for your blessings, and pray for a more peaceful world and a peaceful hurricane season of 2007. Happy Holidays, everyone!

Jeff Masters

Last tropical cyclone of the year?

By: JeffMasters, 2:02 PM GMT on December 21, 2006

Tropical Cyclone Bondo, a major Category 3 storm, is battering the Seychelles Islands between Madagascar and Mozambique today. I expect Bondo will be the final major tropical cyclone of 2006, which has been an active year for intense storms world-wide. Bondo brings the tally of major (Category 3, 4 and 5) tropical cyclones to 29 for the year. The global average for such storms is 24, and the record, 30. This year has also seen 21 Category 4 and 5 cyclones, which is well above the average of 17, but quite a bit short of the record of 25. Bondo is expected to pass very close to Dzaoudzi in the Comoros Islands near 12 UTC on Friday, and is expected to pass between Madagascar and the African coast over the weekend, and possibly strike the northern Madagascar coast as a powerful Category 3 or 4 storm early next week.

Figure 1. Visible image of Tropical Cyclone Bondo taken by NASA's Terra satellite on December 20 at 0635 UTC.

I'll be back Friday with a new blog.
Jeff Masters

New Atlantic tropical storm--from July

By: JeffMasters, 3:21 PM GMT on December 19, 2006

The hurricane season of 2006 has a new tropical storm. No, it's not one of those rare December tropical storms. The new storm occurred back in July, according to a post-season analysis released by the National Hurricane Center Friday. The unnamed storm formed about 240 miles southeast of Nantucket, Massachusetts on July 17 from the remains of a cold front that had pushed off the East Coast on July 13. The unnamed storm started off as an extratropical storm, then passed over the warm 28-29 C waters of the Gulf Stream, which helped it make the transition to a warm-cored tropical storm. At its peak intensity, the unnamed storm had winds of 50 mph at the surface. As it moved northeastward, it passed into much colder waters, and died 24 hours after becoming a tropical storm. There were no reports of damage or injuries.

Figure 1. Unnamed tropical storm of July 17, 2006 (labeled "Extratropical (subtropical?) low" in my blog from July 17).

It is often difficult to be certain in real time if a short-lived storm is fully tropical and deserves a name. If the storm is not a threat to land, NHC will usually play it conservative, and rely on an end-of-season post-analysis using data that is not available in real time to determine if a borderline system was a tropical storm or not. In my blog from July 17 of this year, I noted, "To my eye, the system is probably a subtropical storm, and technically should be classified as Subtropical Depression Two. However, is it difficult to tell for sure, and the NHC is conservatively not naming it, since it is headed towards colder water and has little chance of becoming a full tropical storm." This is the second year in row NHC has analyzed a new tropical storm after the season was over. Last year, "Should have been Tammy" got rooked out of name; this year's storm--"Should have been Beryl"--brings the statistics for the 2006 Atlantic hurricane season exactly to average for named storms--ten--and one below normal for hurricanes, five.

For information about Tropical Cyclone Bondo near Madgascar, which is near Category 5 intensity, see Margie Kieper's excellent View From the Surface blog. The cyclone passed only 37 km south of Agalega, Mauritius, today.

Jeff Masters

A visit to ground zero of Hurricane Charley

By: JeffMasters, 3:09 PM GMT on December 18, 2006

November is a great time to take a Florida vacation. Michigan is horribly grey and cold and dark, and I am always ready for a break after a long hurricane season. This November, I vacationed in one of my favorite haunts, Cayo Costa State Park in Florida. The park is located on an undeveloped barrier island offshore from North Fort Myers, and is reachable only by boat. It was here that Hurricane Charley made its initial landfall in 2004 at 2:45pm EDT 13 August. Charley was a ferocious Category 4 hurricane with maximum sustained winds near 150 mph and a storm surge of at least 7 feet, and was the second most destructive hurricane in history at that time. I expected to see a complete transformation of the island, given the incredible power of this hurricane.

As we approached the island on the Tropic Star ferry boat, I could see considerable evidence of damage to the bay side mangrove trees. Up to 50% of the mangrove trees had been uprooted and killed, leaving large tangles of dead wood along the shore. However, there was plenty of live mangroves, and the bird life seemed as plentiful as I remembered from years past. After we landed and we started piling our camping gear into the shuttle that would take us to our primitive cabin on the Gulf side, I noted that there was no sign Charley had hit, other then a few clumps of dead mangroves along the shore. The native Florida cabbage palms, sea grapes, and other vegetation all looked intact, and the island was impressively green. I was very curious to see what the other side looked like. As we rode over, the ranger informed me that only two of the 20 or so cabins on the island had been destroyed by Charley, although the storm surge had flooded all of them. Almost all of the huge Australian pine trees had been snapped off, he told me, and the rest had been chopped down since they were non-native invasives, anyway. As we arrived, I was surprised to see that other than the missing Australian pines, the place was just as I remembered it. The native vegetation has withstood the hurricane remarkably well, and there were just a few palm trees missing their tops that one could identify as storm victims. The lesson here: natural systems are well equipped to withstand and bounce back from the ravages of mighty hurricanes. Humans would do well to learn the lessons from past storms and do the same!

My next blog will be Tuesday or Wednesday, when I plan to discuss the shrinkage of the Arctic Ice Cap.

Jeff Masters

2006: sixth warmest year on record

By: JeffMasters, 2:36 PM GMT on December 15, 2006

The planet's high fever abated only slightly in 2006 compared to 2005, according to preliminary figures issued by the National Climatic Data Center on Thursday. Following the warmest year on record for the globe in 2005, the annual global temperature for 2006 is expected to be sixth warmest since record keeping began in 1880. The annual averaged global temperature was 0.52�C (+0.94�F) above normal, just 0.09�C below the record set in 2005. Very little of the globe was cooler than normal in 2006--only Siberia had temperatures more than 1� C cooler than average (Figure 1).

Figure 1. Temperature departures from normal for 2006, based on preliminary data from the National Climatic Data Center.

U.S. Temperatures
The 2006 annual average temperature for the contiguous United States (based on preliminary data) will likely be 2�F (1.1�C) above the 20th Century mean, which would make 2006 the third warmest year on record. Only 1998 and 1934 were warmer than 2006. Three months in 2006 (January, April and July) were either the warmest or second warmest on record. Only September and October were cooler than average. A quick look at the jet stream pattern for the remainder of 2006, as forecast by the GFS model, reveals a continuation of the abnormal warmth we've seen over most of the U.S. this month. There will be very few regions of the country experiencing a white Christmas this year.

European temperatures
The Meteorlogical Office of England announced yesterday that 2006 was the warmest year in England since record keeping began in 1659. The years 1990 and 1999 shared the record, previously. The weather this Fall has been the warmest ever recorded over most of western Europe. One UK newspaper trumpeted the headline yesterday, "The hottest year since 1659 spells global doom". I don't agree that the hottest year ever in one small country is evidence that global doom is approaching. However, the statistics of what has happened globally the past 30 years speak volumes. Including 2006, six of the seven warmest years on record have occurred since 2001 and the ten warmest years have occurred since 1995. The global average surface temperature has risen between 0.6�C and 0.7�C (1.1 - 1.3� F) since the start of the 20th Century, and the rate of increase since 1976 has been approximately three times faster than the mean for the past 100 years. If the rate of warming since 1976 (Figure 2)--0.55�C in 30 years--is sustained the remainder of this century, the Earth will be a full 2�C warmer in 2100 than it was in 1990. This amount of warming would be tremendously costly to society and highly damaging to many ecosystems.

Figure 2. Temperature departures from normal for 1880-2006. Source: National Climatic Data Center.

The globe is undeniably warming at rapid rate, and I wouldn't be at all surprised if 2007 surpasses the global temperature record set in 2005, since we are entering 2007 with a moderate El Ni�o event on our hands. El Ni�o conditions add a tremendous amount of heat to the Earth's surface, and the current El Ni�o--which is expected to last at least until May--should drive up global temperatures significantly. Global doom is not at hand, but the predictions by our best climate scientists of a 1.4 to 5.8�C increase in global temperatures between 1990 and 2100 are quite believable and need to be taken seriously.

Next week, I plan to talk about the not-so-cheerful study published in Geophysical Research Letters this week titled, Future abrupt reductions in the summer Arctic sea ice. A sudden and complete disintegration of the North Polar ice cap could happen by 2040, according to some computer model calculations.

Jeff Masters

Climate Summaries

Of dust and hurricanes

By: JeffMasters, 3:40 PM GMT on December 14, 2006

The Saharan Air Layer (SAL) is an layer of dry, dusty Saharan air that rides up over the low-level moist air over the tropical Atlantic. At the boundary between the SAL and low-level moist air where the trade winds blow is the trade wind inversion--a region of the atmosphere where the temperature increases with height. Since atmospheric temperature normally decreases with height, this "inversion" acts to but the brakes on any thunderstorms that try to punch through it. This happens because the air in a thunderstorm's updraft suddenly encounters a region where the updraft air is cooler and less buoyant than the surrounding air, and thus will not be able to keep moving upward. The dust in the SAL absorbs solar radiation, which heats the air in the trade wind inversion. This makes the inversion stronger, which inhibits the thunderstorms that power a hurricane. The dust may also act to interfere with the formation of cloud drops and rain drops that these thunderstorms need to grow, but little is known about such effects.

Figure 1. Map of the mean summer dust optical thickness derived from satellite measurements between 1979 and 2000. Maximum dust amounts originate in the northern Sahel (15 to 18 N) and the Sahara (18 to 22 N). The Bodele depression in Chad is also an active dust source. Image credit: Evidence of the control of summer atmospheric transport of African dust over the Atlantic by Sahel sources from TOMS satellites (1979-2000) by C. Moulin and I. Chiapello, published in January 2004 in Geophysical Research Letters.

The summertime dust that affects Atlantic tropical storms originates over the southwestern Sahara (18 - 22 N) and the northwestern Sahel (15 - 18 N) (Figure 1). The dust that originates in the Southwest Sahara stays relatively constant from year to year. However, the dust from the northwestern Sahel varies significantly from year to year, and understanding this variation may be a key factor in improving our forecasts of seasonal hurricane activity in the Atlantic. The amount of dust that gets transported over the Atlantic depends on a mix of three main factors: the large scale and local scale weather patterns (windy weather transports more dust), how wet the current rainy season is (wet weather will wash out dust before it gets transported over the Atlantic), and how dry and drought-damaged the soil is. The level of drought experienced in the northwestern Sahel during the previous year is the key factor of the three in determining how much dust gets transported over the Atlantic during hurricane season, according to a January 2004 study published in Geophysical Research Letters published by C. Moulin and I. Chiapello. In 2005 (Figure 2), precipitation across the northwestern Sahel averaged near normal, so I'm a bit surprised we saw so much dust over the Atlantic. So far in 2006, precipitation in the northwestern Sahel has been lower than in 2005. If the research cited above is any indication, we should have at least as much dust over the Atlantic during the 2007 hurricane season as the 2006 hurricane season had, which should act to hamper hurricane formation in the region between Africa and the Lesser Antilles Islands.

Figure 2. Departure of precipitation from normal for the African rainy season. Precipiation was near normal averaged across the northwestern Sahel region. Image credit: NOAA.

Jeff Masters

The failure of preseason predictions for the hurricane season of 2006

By: JeffMasters, 2:05 PM GMT on December 12, 2006

The preseason predictions of an extremely active hurricane season were spectacularly wrong. Only nine named storms and five hurricanes formed in the Atlantic, one below the average of ten named storms and six hurricanes. We ended up with the quietest hurricane season since 1997, much to the relief of regions ravaged by the unprecedented activity of 2004 and 2005. What happened to make the prognostications such a abysmal failure?

Dry air and dust
A significant reason for the failure appears to be the unusual amount of dry air laden with African dust that came off the Sahara Desert during July and August. Hurricanes need moist air at mid-levels of the atmosphere in order to form, and recent research suggests that the dust within the dry air may act as an inhibiting factor as well, through some not well-understood process. In addition, these dry air outbreaks are frequently accompanied by a strong jet of easterly winds that brings hostile wind shear over the Atlantic. As seen in a plot of the relative humidity at 500 mb (roughly 18,000 feet altitude) in August of 2006 (Figure 1), there was much drier air than usual over a large portion of the tropical Atlantic where hurricanes like to form.

Why was there so much dry air and dust? During the early part of the rainy season (May-July) in the southern Sahel region of Africa, precipitation was well below average (Figure 2). Rainfall was also below average in this region in 2005, and these factors could have contributed to more Saharan dust being blown out over the tropical Atlantic in 2006.

Figure 1. Departure from normal of relative humidity for the month of August, at 500 mb (about 18,000 feet altitude).

Figure 2.Departure of precipitation from normal for May-July 2006 for Africa. Note that the southern Sahel region (approximately 10-15N, 0-15W) had much below average precipitation, and this likely contributed to the dry air and widespread Saharan dust outbreaks observed over the tropical Atlantic this year. Image credit: Bill Gray and Phil Klotzbach's Summary of 2006 Atlantic Tropical Cyclone Activity and Verification of Author's Seasonal and Monthly Forecasts at Colorado State University.

El Nio
The other reason the hurricane season of 2006 was so mild is probably due to the arrival of El Nio conditions in September. It is well known that when the warming of the Equatorial Pacific waters off the coast of South America brings about an El Nio event, the number and intensity of Atlantic hurricanes is sharply reduced. Conversely, action in the Eastern Pacific is enhanced, and we saw both of these effects in 2006. The reason usually given for this lack of activity in the Atlantic is an increase in wind shear. The warm waters of the eastern Pacific lead to more rising air than usual there, and when that rising air hits the top of the troposphere (the lower atmosphere), it spreads out and creates strong upper-level winds that blow from east to west towards the Western Pacific, and west to east over the Atlantic. These strong upper-level winds create hostile wind shear that tears apart developing hurricanes. However, in 2006, it appears that El Nio-induced wind shear was not a serious impediment to Atlantic hurricane formation. Wind shear was near average over the Atlantic during most of hurricane season (Figure 3). There are additional reasons El Nio suppresses hurricane activity, and foremost among these is the introduction of stable, sinking air over the Atlantic. It is likely that El Nio brought such conditions to the Atlantic during large portions of the 2006 hurricane season, significantly inhibiting hurricane formation.

Figure 3. Wind shear over the tropical Atlantic. Except for a big above-normal spike in October, wind shear in 2006 (blue line) was near normal (black line) over the tropical Atlantic during hurricane season. Image credit: NOAA/CIRA.

So why did the long range forecasts fail?
The long range seasonal hurricane predictions are statistical in nature--they look for early season patterns in winds, pressures, and ocean temperatures that occurred in years past that one can combine to make a skillful prediction of the hurricane season. One of the variables these prediction schemes typically do not include is the early season rainfall in Africa. If it is an unusually dry and dusty year over the Atlantic like 2006 was, then the forecast is going to be wrong. The other problem was the unusual nature of the El Nio event that developed this year. We went from La Nina conditions in March to a full-fledged El Nio in September. This was by far the largest percentage warming of SST anomalies between June-July and August-September in the tropical Pacific for a year that had El Nio conditions in August-September. In addition, the the timing was unusual--it is uncommon for El Nio events to start in the Fall. Since the historical record had very few cases mimicking the behavior of this year's El Nio event, it is no wonder that the statistical models which rely on past years' data to come up with forecasts of hurricane activity failed. El Nio behaved too strangely this year to anticipate, and the computer models had no idea it was coming until about March or April.

Jeff Masters

Philippines clean up after Utor

By: JeffMasters, 7:03 PM GMT on December 11, 2006

The Philippine Islands continue to assess the damage from Typhoon Utor (called Seniang in the Philippines). Utor (the Marshallese word for a squall line) hit the eastern Samar province Saturday as a Category 1 typhoon on Saturday, then intensified to a Category 3 typhoon as it passed through the islands, striking Mindoro Island as a Category 3 storm before passing out into the South China Sea. Thankfully, Utor moved at a much quicker speed through the islands than devastating Super Typhoon Durian did at the end of November, and thus dropped only about half the amount of rain. The death toll from Utor is 6, with 19 missing. Most of the missing are fisherman that may yet be found. Utor did not trigger major mudslides and flash flooding like Durian did, and the storm is expected to die in the South China Sea and not create significant problems for any other nations. A list of the typhoons to hit the Philippines so far this year, and their strength at landfall:

Chanchu (May) Cat 2
Xangsane (Sept) Cat 4
Cimaron (Oct) Cat 5
Chebi (Nov) Cat 3
Durian (Nov) Cat 4
Utor (Dec) Cat 3

Utor was unusual in that it intensified significantly from a Category 1 storm with 75 mph winds to a Category 3 storm with 115 mph winds while it passed through the islands with much of its circulation over land. Normally, the friction created when a typhoon's winds pass over land will weaken the storm. In Utor's case, however, the inner core of the storm remained over warm (29 C) waters, and it may be that the funneling effect of the low-level wind flow through the spaces between the islands acted to accelerate the winds flowing into the eyewall. These faster winds near the core brought in more water vapor to fuel the storm and generated enhanced updrafts in the eyewall, allowing the typhoon to intensify despite the frictional drag of land on the rest of the storm. It is also possible that the relatively protected waters between the islands allowed the large waves kicked up by the storm to die down, reducing the amount of frictional drag on the winds and thus aiding intensification. A detailed computer simulation of the air-sea interaction of Utor is needed to figure out what happened, though.

Figure 1. Satellite image of Typhoon Utor from NOAA.

Jeff Masters

Space Shuttle blazes into space; Utor pounds Philippines

By: JeffMasters, 12:58 PM GMT on December 10, 2006

The Space Shuttle Discovery lifted off last night in a rare and impressive nighttime launch, beating the weather forecast that called for only a 30% chance of success. Wunderblogger Mike Theiss took some fantastic photos of the event.

Yet another typhoon for the Philippines
Typhoon Utor (called Seniang in the Philippines) became the 5th major typhoon to hit the storm-weary Philippines this season, when it intensified suddenly last night from a Category 1 to a Category 3 typhoon (Utor is the Marshallese word for a squall line). The storm put on the burst of intensification as it approached San Jose on Mindoro Island, where the pressure dropped to 985 mb and top winds of 50 mph were recorded. There are no damage reports from this hardest-hit island yet, but Utor killed 3 and left 3 missing when it initially came ashore as a Category 1 typhoon in eastern Samar province at noon Saturday. Utor brought much less rain than its predecessor, Super Typhon Durian. Rainfall estimates from Utor (Figure 1) were in the 4-6 inch range for a 24 hour period. Durian dumped up to 10 inches in 24 hours. It is unlikely that the rains of Utor caused significant loss of life due to major mudslides and flash floods, but many more Philippinos will join the ranks of the 300,000 left homeless by Super Typhoon Durian. Utor did not trigger new mudslides along the flanks of the Mayon Volcano where over 1,000 people died in Super Typhoon Durian. Utor may intensify now that it is over the warm, open waters of the South China Sea. The typhoon is expected to turn north and threaten China and Taiwan later this week. NOAA has some nice satellite imagery of the storm at their West Pacific floater imagery page.

Figure 1. Rainfall estimates for Typhoon Utor from NOAA.

Super Typhoon Durian left 1339 dead or missing the Philippines, injured 2000, destroyed 118,000 homes, and damaged 212,000 homes. In Vietnam, Durian killed 89, injured 1370, destroyed 35,000 homes, and damaged another 182,000 homes. Total damage was estimated at about $31 million in the Philippines.

Jeff Masters

2007 Hurricane Season Forecast

By: JeffMasters, 5:50 PM GMT on December 08, 2006

It's going to be a more active than usual Atlantic hurricane season in 2007, but not hyperactive, according to the latest seasonal forecast issued by Dr. Bill Gray and Phil Klotzbach of Colorado State University today. The Gray/Klotzbach team is calling for 14 named storms, 7 hurricanes, and 3 intense hurricanes. An average season has 10 named storms, 6 hurricanes, and 2 intense hurricanes. The forecast calls for an above normal chance of a major hurricane hitting the U.S., both along the East Coast (40% chance, 31% chance is normal) and the Gulf Coast (40% chance, 30% chance is average).

The forecasters predict that the current moderate El Nino event will dissipate by the time the active part of the 2007 hurricane season rolls around. The sudden development of El Nino this year significantly reduced the hurricane activity, and dissipation of this El Nino by August of 2007 would likely create more favorable conditions for hurricane development than in 2006. Gray and Klotzbach support this forecast by examining the active hurricane periods of 1950-1969, and 1995-2005, and note that seven out of the eight seasons following El Nino years during this period were active Atlantic hurricane seasons, and all of these years witnessed either neutral or La Nina conditions.

The forecasters examined the observed atmospheric conditions and ocean temperatures in October-November 2006, and came up with a list of four past years that had a similar combination of a moderate El Nino event, warmer than average tropical Atlantic SSTs, and a weaker-than-normal Azores-Bermuda High. We can expect 2007 to be similar to the average of these four analogue years, they say. The four years were 2003 (16 named storms, 7 hurricanes, 3 intense hurricanes), 1966 (11, 7, and 3 of the same), 1958 (10, 7 and 5), and 1952 (7, 6 and 3). Hurricane Isabel of 2003 (Category 2) was the strongest hurricane to hit the U.S. in these four analogue years, and Category 4 Hurricane Inez of 1966 caused the most death and destruction, killing over 1000 people in its rampage through the Caribbean.

2007 Atlantic hurricane season forecast from Tropical Storm Risk, Inc.
It's going to be a bit rougher year than the Gray/Klotzbach team is forecasting, according to the British private forecasting firm Tropical Storm Risk, Inc. (TSR), who issued their 2007 Atlantic hurricane season forecast yesterday. TSR is calling for a season with 60% above normal activity--16 named storms, 9 hurricanes, and 4 intense hurricanes. They project that five named storms will hit the U.S., with two of these being hurricanes. In the Lesser Antilles Islands of the Caribbean, TSR projects two named storms, one of them being a hurricane. TSR cites two main factors for their forecast of an active season: above normal Sea Surface Temperatures (SSTs) are expected in August-September 2007 across the tropical Atlantic, as well as slower than normal trade winds. Trade winds are forecast to be 0.7 meters per second (about 1.5 mph) slower than average, which would create greater spin for developing storms, and allow the oceans to heat up due to reduced evaporational cooling. SSTs are forecast to be about 0.34 degrees C above normal. TSR gives an 80% chance that the 2007 Atlantic hurricane season will rank in the top third of active seasons observed since 1957.

Figure 1. Accuracy of long-range forecasts of Atlantic hurricane season activity performed by Bill Gray and Phil Klotzbach of Colorado State University (colored squares) and TSR (colored lines). The skill is measured by the Mean Square Skill Score (MSSS), which looks at the error and squares it, then compares the percent improvement the forecast has over a climatological forecast of 10 named storms, 6 hurricanes, and 2 intense hurricanes. TS=Tropical Storms, H=Hurricanes, IH=Intense Hurricanes, ACE=Accumulated Cyclone Energy, NTC=Net Tropical Cyclone Activity. Image credit: TSR.

How good are these December hurricane season forecasts? Unfortunately, they're pretty much worthless. The skill of the December forecasts issued by Dr. Gray and TSR (Figure 1) have averaged near zero since 1992. Not surprisingly, the forecasts get better the closer they get to hurricane season. The June and August forecasts show some modest skill, and are valuable tools for insurance companies and emergency planners to help estimate their risks. The problem with the December forecasts is that the current statistical computer models used to forecast El Nino are not skillful beyond about six months. For example, none of these models foresaw the current El Nino event that began in September--until April. Until we can forecast the evolution of El Nino more than six months in advance, these December forecasts are not worth paying much attention to. I think it's important for these groups to keep trying, though.

I'll be back Monday with a new blog. Tune into the blog of Mike Theiss this weekend, he'll be covering the launch of the Space Shuttle. Mike is a top notch storm chaser and weather photographer we're excited to have on our wunderblogging team!

Jeff Masters

Bill Proenza named new NHC director; new typhoon for Philippines?

By: JeffMasters, 2:31 PM GMT on December 07, 2006

We don't know him yet, but soon the face and voice of Bill Proenza will become a familiar part of our hurricane experience. As reported by Wunderblogger Margie Kieper in her View From the Surface blog yesterday, the new director of the National Hurricane Center (NHC) is Bill Proenza, 62, a 40-year veteran of the National Weather Service (NWS). Bill currently serves as director of the NWS Southern region, which includes hurricane-prone Florida, Alabama, Mississippi, Louisiana, Texas, and Puerto Rico. He certainly has the experience, knowledge, and connections to make a great NHC Director, and I wish Bill the best of luck in this most demanding of meteorology jobs!

New NHC Director Bill Proenza. Image credit: NOAA.

New typhoon for the Philippines?
A new typhoon is brewing in the waters to the east of the Philippine Islands. Tropical Storm Utor (named after the Marshallese word for "squall line") has the potential to grow to typhoon strength before it makes landfall in the central Philippines Saturday. The storm is under only 5 knots of vertical wind shear, and satellite imagery from the Navy NRL web site shows a large, well-organized system with excellent upper-level outflow, impressive spiral banding, and a steadily consolidating area of heavy thunderstorms near the center. Utor is organizing closer to the Philippines than Durian did, and is moving more rapidly--15 mph. This likely means the storm does not have enough time to grow into a super typhoon like Durian did. Even if Utor does become a major typhoon, its fast forward speed means it will not have enough time over the islands to dump the kind of heavy rains that would cause significant loss of life. The typhoon-weary Philippines could sure use a break! The toll in the islands from Typhoon Durian stands at 1316 dead or missing, 1,933 injured, 80,000 homes destroyed, and 167,000 homes damaged. The estimated $600 million in damage is the highest ever for a Philippines typhoon, and the death toll is the 4th highest. The typhoon killed 105 people in its sweep past southern Vietnam, mostly due to high winds that collapsed buildings. Durian destroyed or damaged over 212,000 homes in Vietnam, and sank 808 fishing boats.

Bill Gray's 2007 hurricane season forecast
Friday, I'll review Bill Gray's 2007 hurricane season forecast, scheduled to be released late in the morning.

Jeff Masters


New NHC Director to be announced today

By: JeffMasters, 2:21 PM GMT on December 06, 2006

The new director of the National Hurricane Center (NHC) will be named today during a press conference scheduled to begin at 2:30pm EST. Max Mayfield, 58, NHC director since 2000, is stepping down in January. The difficult hurricane seasons of 2004 and 2005 wore him out, he said, and he wanted to retire to spend more time with his family. Who can blame him? Director of NHC is a very demanding job even in the off season--Max stated that he spent about four months traveling during December through May attending various conferences and hurricane awareness functions. I'll be very sorry to see Max go--his combination of forecasting skills, ease of communication with the public, and dedication to his work made him a great NHC director.

Max Mayfield, retiring National Hurricane Center director. Image credit: NOAA.

Most of the senior hurricane specialists at NHC in line to take over from Max declined to apply for the job, and it appears that first the first time ever, someone from outside the NHC or NOAA's Hurricane Research Division will get the job. Speculation currently centers on Bill Proenza, 62, director of the National Weather Service's Southern Region, which includes Florida, Texas, Louisiana, Mississippi and Alabama.

Wunderblogger Margie Kieper will be dialing into today's press conference, and plans to post a blog shortly after 3pm EST announcing the new NHC director in her View From the Surface blog. Tune in then!

Typhoon Durian is no more
The violent rampage of Typhoon Durian has finally come to end. Durian made landfall yesterday in Thailand's southern province of Chumphon as a tropical depression, causing heavy rain but no significant damage or injuries. Durian dissipated while making landfall, and will trouble the world no longer. The typhoon killed 61 people in its sweep past southern Vietnam, mostly due to high winds that collapsed buildings. Durian destroyed or damaged over 120,000 homes in Vietnam, and sank 850 fishing boats. The toll in the Philippines stands at 1266 dead or missing, the fourth highest toll ever recorded from a typhoon there. Durian destroyed 76,000 homes and damaged 154,000, and the estimated $600 million in damage was the highest ever for a Philippines typhoon.

Figure 2. Final rainfall estimates from NASA's TRMM satellite for Typhoon Durian. 250 mm = about 10 inches of rain.

Next blog
Friday, I'll discuss Dr. Bill Gray's first forecast for the 2007 hurricane season, which is scheduled to be released late in the morning Friday.

Jeff Masters

Durian: worst tropical cyclone of 2006

By: JeffMasters, 3:49 PM GMT on December 04, 2006

The death toll in the Philippine Islands from Typhoon Durian (called Typhoon Reming in the Philippines) now stands at 1226 dead or missing, according to Philippine disaster officials, and is certain to go higher as rescue workers continue to recover bodies from mudslides that buried at least eight villages at the foot of Mayon Volcano. Durian is now the third most deadly tropical cyclone to strike the Philippines since 1946, according to a list maintained at The worst storm, Tropical Storm Thelma, killed 5,100-8,000 people in 1991 when torrential rains caused flash floods on over-logged hills surrounding Ormoc City in Leyte. A river flowing through the city burst its banks, and drowned over 1/4 of the residents. The second most deadly was Typhoon Ike of September 1, 1984, which killed 1300-3000 due to flooding and mudslides from torrential rains. Like Durian, Ike was a 145-mph Category 4 typhoon at landfall, but Thelma never even made it to typhoon status. The Philippines have also suffered calamitous mudslides and flooding from heavy rains associated with La Nia events, as occurred in February 2006 when 3000 people died on Leyte Island. The worst flooding disaster ever to affect the Philippines that I could find record of was the typhoon of November 6, 1885, which killed 10,000 when a huge storm surge roared ashore on the Tiburon Peninsula. Durian has surpassed Tropical Storm Bilis as the deadliest tropical cyclone to affect the globe in 2006. Bilis killed 662 people in July, primarily due to severe flooding in China.

Figure 1. Rainfall estimates from NASA's TRMM satellite on November 29, 2006, as Typhoon Durian approached the Philippines. Durian brought 8-12 inches of rain along its path.

The region Durian hit has been visited by at least one other typhoon of similar intensity. On November 25, 1987, Typhoon Nina hit the Mayon Volcano region as a category 5 super typhoon. A pressure of 909.5 mb was measured at Legaspi, the lowest pressure ever recorded in the Philippines. Mudslides and flash floods roaring down the Mayon Volcano killed 600-1100 people.

The damage caused by Durian has been extreme. Nearly 300,000 homes have been destroyed or damaged. Damage to agriculture has been exceptionally heavy, as well. Total damage estimates are at $643 million, making Durian by far the most costly typhoon in Philippine history. The previous most costly typhoons did damage in the $100-$200 million dollar range.

Durian sideswiped southern Vietnam Monday as a weak Category 1 typhoon, but its winds were strong enough to kill 49 people there, and damage or destroyed 58,000 homes. Durian is expected to become a rare ocean-to-ocean tropical cyclone when it crosses the Malay Peninsula Wednesday and enters the Indian Ocean in the Bay of Bengal. Dry air is expected to keep the storm below typhoon strength for the remainder of its life.

I'll update this blog Wednesday afternoon, when the new head of the National Hurricane Center will be announced.

Jeff Masters

Typhoon death toll 800 and rising

By: JeffMasters, 5:13 PM GMT on December 02, 2006

The terrible toll wrought by Typhoon Durian is just beginning to be known, as rescue workers in the Philippines dig out victims from mudslides that buried at least eight villages at the foot of Mayon Volcano. The volcano, a 2460 meter-high mountain known for its perfect conical shape, had large areas of loose rock from a July eruption that became loosened by Durian's 8-12 inches of rain. The loose rock turned into torrents of liquid mud that swept down the mountain in the form of deadly mudslides, burying entire villages up to their rooftops. At least 800 people are dead or missing, and the head of the Philippines Red Cross estimated on Sunday that the toll would surpass 1000. Many hard-hit areas still unreachable and cut off from communications. Durian has surpassed Tropical Storm Bilis as the deadliest tropical cyclone to affect the globe in 2006. Bilis killed 662 people in July, primarily due to flooding in China.

The Manila Bulletin Online, said that some of the mud flows were up to 100 feet deep.

Figure 1. Topographic map of the Mayon Volcano region hard-hit by Typhoon Durian. Image credit: United Nations UNOSAT project, providing free maps for the humanitarian community.

Durian has unexpectedly strengthened to a Category 2 typhoon over the South China Sea, and may yet cause some trouble when it strikes Vietnam on Monday, most likely as a Category 1 typhoon. The View from the Surface blog has more info on the latest doings of Durian.

I hope that those of you looking for charities to donate to this year will join me in donating to the Red Cross International Response Fund to help out victims of Typhoon Durian. The Philippine National Red Cross does not take on-line donations, but there is contact information posted there for those who want to donate directly to the Philippine Red Cross.

I'll be back with an update on Monday.
Jeff Masters

Typhoon Durian kills at least 388 in Philippines

By: JeffMasters, 3:30 PM GMT on December 01, 2006

At least 388 people have died in the Philippines due to the landfall of devastating Typhoon Durian, which slammed ashore in the central Philippine Islands yesterday. Durian hit extreme southern Luzon Island in the province of Albay as a Category 4 storm with sustained winds of 145 mph. The typhoon passed directly over Mayon, the most active volcano in the Philippines and one of the country's most famous tourist attractions because of its near-perfect cone. Loose rock that the volcano had deposited in a July eruption rushed down the slopes in the form of deadly mudslides, thanks to Durian's torrential rains. Estimates from NASA's TRMM satellite of the rain amounts were 8-12 inches in a 24 hours period. The mudslides swept into villages and rivers at the foot of the Mayon Volcano. Evacuations of the villages had not been ordered, since the region had never before experienced severe mudslides from a typhoon.

Next, Durian hit the island of Marinduque as a Category 3 typhoon with sustained winds of 120 mph. Virtually every building on the island was damaged or destroyed, and Durian was judged the worst typhoon ever to hit the island. In all, the death toll from Durian makes this storm more deadly than Typhoon Xangsane, which killed 218 people in the Philippines on September 27. Durian is the fourth major typhoon to hit the Philippines this year.

Figure 1. Visible satellite image from NASA's Aqua satellite of Typhoon Durian from 05 GMT November 30, 2006 (1pm local time in the Philippines). The Mayon volcano was in the southern eyewall underneath an impressive tower of high cumulonimbus clouds at the time. Image credit: NASA.

Durian is now a weakening Category 1 typhoon over the South China Sea, and is expected to weaken further as it continues westwards towards Vietnam. A large area of dry air over the region should reduce Durian to tropical storm strength by the time it reaches Vietnam on Monday, where it is not expected to do significant damage.

I'll save my discussion of why the 2006 hurricane season was so mild for next week. Expect a short update on Durian Saturday.

Jeff Masters

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

Category 6™


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