Dr. Jeff Masters' WunderBlog

Delta destroys God's Finger

By: JeffMasters, 4:23 PM GMT on 十一月 30, 2005

Today marks the official final day of hurricane season, but the Hurricane Season of 2005 continues to show little regard for climatology. Tropical Storm Epsilon will linger at least until December 2, when strong wind shear and passage over cooler waters to the northeast are likely to reduce Epsilon to an ordinary extratropical storm. Epsilon's formation marks the first time on record that three tropical storms have formed in November. The previous record was two November storms, which occurred six times, most recently in 2001.

Epsilon is over ocean waters with temperatures of 23 - 25C, which are too cold to support a fully tropical system. Epsilon is a hybrid "subtropical cyclone"--one that gets its energy from both the warm water of the oceans and the temperature differences of cold and warm airmasses interacting. The difference between a subtropical storm and a tropical storm is not that important as far as the winds they can generate--Epsilon is near hurricane strength, and could well become a hurricane by this time tomorrow.

Delta destroys God's Finger
Tropical Storm Delta was declared extratropical at 10am Monday, so the deaths and damage it inflicted on the Canary Islands Monday night will probably not be counted in the official statistics for the Hurricane Season of 2005. Nevertheless, Delta was the first tropical cyclone in recorded history to affect the Canary Islands--a check of the tracks of storms since 1851 shows no other tropical storm has come within 500 miles of the islands. Delta dealt the popular tourist mecca a stunning blow that will be remembered for generations to come. Delta toppled the signature landmark of the islands, a narrow finger of rock called "God's Finger" that jutted out of the ocean. The Tenerife News, a local paper from the Canary Islands, reported it thusly:

The emblematic rocky pinnacle known as El Dedo de Dios or Gods Finger, which had pointed skywards from the sea for millennia, a natural wonder and one of the must-see sights of the archipelago finally gave up the ghost after thousands of years and collapsed into the broiling sea. The news of the loss has left islanders in a state of shock.



El Dedo de Dios (God's Finger)
Image credit: http://www.grancanariaschool.com

I'll be back tomorrow with Part I of a multi-part summary of this year's hurricane season--why was the U.S. hit so often, and why did Puerto Rico and the northern Leeward Islands escape harm?

Jeff Masters

Updated: 4:49 PM GMT on 十一月 30, 2005

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Amazing! It's Epsilon

By: JeffMasters, 8:01 PM GMT on 十一月 29, 2005

The official end of hurricane season lies only two days away, but the all-time records set by the Hurricane Season of 2005 continue to grow. Epsilon has become the 26th tropical storm of the season--far exceeding the previous record 21 storms seen in 1933. Epsilon may grow into the 14th hurricane this year, extending this year's record number of hurricanes to two more than the 12 hurricanes observed in 1969. Epsilon is really a hybrid between a tropical storm and a regular extratropical storm,
but its winds are nevertheless of tropical storm strength. Both Delta and Epsilon are more properly termed "subtropical" storms, but I guess the Hurricane Center has stopped calling storm "subtropical" to avoid confusion. Subtropical storms gain their energy not only from the warm ocean waters--like hurricanes do--but also from the release of potential energy created when cold and warm airmasses interact--like extratropical storms do. Epsilon is unlikely to strike any land areas, and will probably recurve to the north and east late in the week and be absorbed by a cold front sweeping over the north Atlantic Ocean.


Figure 1. Model forecasts for Epsilon.

Delta hits Canary Islands hard
Tropical Storm Delta slammed into Spain's Canary Islands last night at near hurricane strength, killing at least seven people. One man died when he was blown off the roof he was trying to repair, and six African illegal immigrants drowned after winds caused their boat to capsize while attempting to reach Gran Canaria Island. Twelve of the immigrants remained missing while 32 were rescued. Each year, thousands of migrants try to reach the Canary Islands from Africa and many die in the attempt, but usually not in a tropical storm!

Sustained winds of 71 mph gusting to 86 mph were recorded at Tenarife, and a wind gust of 94 mph was recorded at La Palma. The near hurricane force winds caused extensive damage to utility poles, roofs, and trees all across the islands, which are a popular tourist destination for Europeans. Power is still out to over 223,000 residents today, but is expected to be restored to a large majority by Wednesday. Delta weakened considerably after smashing through the Canary Islands, and came ashore in Morocco this morning with only 45 mph winds gusts and some isolated pockets of heavy rain. Delta's rains were expected to provide a boon to local farmers unaccustomed to heavy precipitation.

Jeff Masters

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Delta slams Canary Islands; Epsilon next?

By: JeffMasters, 2:58 PM GMT on 十一月 29, 2005

Tropical Storm Delta slammed into Spain's Canary Islands last night at near hurricane strength, killing at least seven people. One man died when he was blown off the roof he was trying to repair, and six African illegal immigrants drowned after winds caused their boat to capsize while attempting to reach Gran Canaria Island. Twelve of the immigrants remained missing while 32 were rescued. Each year, thousands of migrants try to reach the Canary Islands from Africa and many die in the attempt, but usually not in a tropical storm!

Sustained winds of 71 mph gusting to 86 mph were recorded at Tenarife, and a wind gust of 94 mph was recorded at La Palma. The near hurricane force winds caused extensive damage to utility poles, roofs, and trees all across the islands, which are a popular tourist destination for Europeans. Power is still out to over 223,000 residents today, but is expected to be restored to a large majority by Wednesday. Delta weakened considerably after smashing through the Canary Islands, and came ashore in Morocco this morning with only 45 mph winds gusts and some isolated pockets of heavy rain. Delta's rains were expected to provide a boon to local farmers unaccustomed to heavy precipitation.

Now that Delta is gone and the official end of hurricane season lies only two days away, we must ask--is hurricane season over? Of course not! This is the Hurricane Season of 2005, and naturally there is another area of disturbed weather we need to be concerned about. A large non-tropical low pressure system in the mid-Atlantic near 30N 50W continues to look impressive, with two areas of deep convection firing up near its center. Wind estimates from the military's F-14 polar orbiting satellite show winds of 30 - 40 mph near the heaviest convection. If this convection manages to wrap all the way around the center of the center of circulation, the NHC will likely start issuing advisories on Tropical Storm Epsilon. This does not appear likely to happen today, but could occur on Wednesday or Thursday as the storm slowly moves westward towards Bermuda. This system is unlikely to reach Bermuda, and will probably recurve to the north and east late in the week and possibly threaten the Azores Islands.


Figure 1. Early track model forecasts for the tropical low that may turn into Epsilon.


Jeff Masters

Updated: 3:03 PM GMT on 十一月 29, 2005

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Delta done; Epsilon next?

By: JeffMasters, 3:48 PM GMT on 十一月 28, 2005

Delta is now a formidable non-tropical (also called extra-tropical) low-pressure system over the far eastern Atlantic. Delta has merged with a cold front approaching the coast of Africa, and this cold front will sweep Delta's remnants through the Madeira Islands today and into the Morocco on Tuesday, battering those areas with a ferocity rarely seen. Winds should reach 50-60 mph, accompanied by rains of 3-6 inches and a storm surge of 2-4 feet. Welcome to the Hurricane Season of 2005, northern Africa!

With Delta's demise today, there is a possibility that the Hurricane Season of 2005 is finally over. However, spinning to the west of Delta over the mid-Atlantic Ocean is the next system to be concerned about, a large non-tropical low pressure system near 30N 50W. This low is over waters of about 26C (79F), which is right at the threshold where tropical storm development can occur. Already, the storm has winds of tropical storm force (40 mph) in a band to the west of the center, according to a 5am EST pass by the QuikSCAT satellite. This cyclone is expected to move slowly west towards Bermuda the rest of the week, and may gradually acquire enough tropical characteristics to be classified as Tropical Storm Epsilon. The storm has little chance of affecting any land areas except Bermuda, and I expect the storm will recurve back to the east before it reaches Bermuda.


Figure 1. Visible satellite image from 8:30am EST today showing Delta approaching the Madeira Islands and Morocco. To the west of Delta is a non-tropical low that may transform into Tropical Storm Epsilon later this week.

December storms
What are the chances of another tropical storm in December? Wind shear levels in the Caribbean are forecast to remain high this week, so development there is unlikely until next week at the earliest, but I wouldn't count out the Caribbean quite yet this year. Development in the mid-Atlantic area after Epsilon leaves is a possibility. Nothing that develops in either of these areas is likely to develop into a hurricane and affect any land areas, however. Shear levels are probably too high and the oceans too cold to allow a significant hurricane to develop.

Historically, the odds do not favor December tropical storm formation. Between 1871 and 2004, only eight tropical storms formed. Three became hurricanes. Two years had two December tropical storms each--2003 and 1887. Hurricane Alice of 1954 was remarkable in that it formed on December 30, and struck the Lesser Antilles islands of St. Kitts and Barthelemy as a Category 1 hurricane on January 2, 1955. Over $100,000 in damage was caused on the islands, and the rains ended a severe drought in Puerto Rico. The head of Puerto Rico's weather station noted:

"This storm has aroused considerable interest. People were somewhat skeptical and slow in believing that a hurricane had actually formed. Already historians have expressed their opinion as to whether this was, or not, the first of its kind in the area. In Puerto Rico a controversy centers about a storm that affected this island in the year 1816; one historian maintaining that it occurred in the moth of January while another holds that it occurred in September."

Alice was not the only winter hurricane to affect the Caribbean; an unnamed Category 2 hurricane moved through the northern Leeward islands on March 8, 1908.

Tropical Storm Odette was the only December tropical storm to kill anyone--it claimed eight lives in the Dominican Republic due to floods when it struck on December 6, 2003, with winds of 65 mph. Odette downed trees and power lines, and damaged buildings, bridges, and large areas of agricultural land. Approximately 35% of the Dominican Republic's banana crop was destroyed.

So in summary, I do expect we'll get at least one and possibly two more tropical storms this season, but they will not be a threat to cause significant damage to land areas.

Jeff Masters

Updated: 3:54 PM GMT on 十一月 28, 2005

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Delta almost done; is hurricane season over?

By: JeffMasters, 2:45 PM GMT on 十一月 27, 2005

Tropical Storm Delta continues churning over the far eastern Atlantic, and still has a day of life left in it before cold waters and high wind shear tear it apart and transform it into a powerful extratropical storm on Monday. Delta will probably bring heavy rains and winds gusts to 40 mph to the Canary Islands on Monday and Morocco on Tuesday. Delta is following a track no November tropical storm has ever taken--a check of the Historical Map shows that there has never been a November tropical storm in the far eastern Atlantic. Yet another first for the Hurricane Season of 2005!

If Delta dies tomorrow, as expected, will tomorrow then mark the final day of the incredible Hurricane Season of 2005? I'll have a full analysis of the possibilities on Monday, including a discussion of the historical occurrences of hurricanes after December 1.

Jeff Masters

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Back from vacation

By: JeffMasters, 4:40 PM GMT on 十一月 25, 2005

Happy Thanksgiving, everyone! It's good to be back home after a relaxing visit to the Caribbean. I must admit, though, that scraping the inch of ice off of my windshield at the airport in Detroit last night in -5 wind chill temperatures was a shock, after wading in 82 degree waters in San Juan yesterday morning!

I did keep a watchful eye on the tropics while I was in Puerto Rico, because this hurricane season is not yet over. Water temperatures are still more than 80F (26.5 C) over a large portion of the Caribbean and tropical Atlantic, and wind shear levels are still forecast to remain low enough to support formation of a tropical storm Epsilon before the season mercifully ends. In addition to Tropical Storm Delta, there are two areas to watch over the next week:

1) A strong non-tropical low is expected to form by Sunday in the mid-Atlantic just west of Delta's current position, and drift slowly west or west-southwest. Like Delta did, this low could remain over warm water long enough to gradually acquire a warm core and morph into a tropical storm. It is unlikely that this storm would threaten any land areas except Bermuda, the Azores, or Canary Islands.

2) The region just north of Panama may get active, as wind shear levels are expected to be low the next five days. However, there is not much moisture in the region at present, and wind shear values are expected to greatly increase over the entire Caribbean by early December. I don't expect any serious storm will develop in the Caribbean over the next week, although a weak tropical storm is a slight possibility.

Tropical Storm Delta
Delta is still hanging tough in the face of 30-40 knots of wind shear, but its days are numbered. High shear, dry air, and cooler waters will all conspire to weaken Delta over the next two days, then destroy it by Monday. The deep convection around the eye is already starting to decay, and this storm has missed its chance to become a hurricane. The remnants of Delta have the potential to bring 40 mph winds and heavy rain to the Canary Islands and Morocco early next week.

I'll be back with an update on Sunday morning--or Saturday--if something develops worth talking about.

Jeff Masters

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Delta

By: JeffMasters, 10:52 PM GMT on 十一月 23, 2005

This is Tim Roche in for Dr. Masters.
Tropical Storm Delta was classified as a tropical storm as of the 4:00pm EST update from the National Hurricane Center. Delta formed out of a non-tropical low pressure system that has been slowly aquiring tropical characteristics, while drifting eastward over the Atlantic since the middle of last week. Convection wrapped almost all the way around the center earlier today, and a recent Quikscat pass showed several areas with uncontaminated 50kt wind vectors. The system is forecast to drift southward for the next few days then to accelerate northward and lose its tropical characteristics. As Delta becomes extratropical, it will likely strengthen more, with winds possibly reaching hurricane strength. Delta shouldn't effect any landmasses as a tropical storm, and is mostly a threat to nautical interests.

Figure 1. Official NHC 5 day forecast

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PBS Special

By: JeffMasters, 7:24 AM GMT on 十一月 21, 2005

The PBS documentary program Frontline will be airing an episode about Hurricane Katrina on Tuesday, November 22, 2005, at 9 pm. From the PBS press release on this episode:


In the wake of Hurricane Katrina, FRONTLINE investigates the chain of decisions that slowed federal response to the devastation in New Orleans. The film exposes how and why federal and local officials failed to protect thousands of Americans from a broadly predicted natural disaster and examines the state of America's disaster-response system, restructured in the wake of 9/11, on The Storm, airing Tuesday, November 22, 2005, at 9 P.M. EST on PBS (check local listings).

FRONTLINE correspondent Martin Smith (Private Warriors) interviews a comprehensive lineup of key participants from New Orleans to Washington, including former Federal Emergency Management Agency Director Michael Brown in his first televised interview since he resigned. Other interviewees include Louisiana Gov. Kathleen Blanco, New Orleans Mayor Ray Nagin, former Homeland Security Secretary Tom Ridge and former Deputy Secretary James Loy.


Also at 8 pm EST the same night, PBS is airing a NOVA episode on the science of Hurricane Katrina. The show is called Katrina: Storm That Drowned a City. From the press release:


In less than 12 hours on August 29, Hurricane Katrina transformed a city into an uninhabitable swamp. NOVA investigates a shaken New Orleans in the storm's aftermath, providing a penetrating analysis of what science got right, what went wrong, and what can be done in the future, punctuated with moving eyewitness testimony and exclusive expert interviews.


Both Frontline and NOVA have a history of producing excellent shows, and both of these programs should be far more worthy of watching than last Sunday's awful "Category 7: End of the World"! I can't really believe this, but my co-worker's daughter is going to watch this movie in her middle school science class. The educational value of this movie was less than zero. It falls in the realm of bad science fiction, like the 2004 disaster epic, The Day After Tomorrow. FYI, the basic premise of Category 7: End of the World--that two huge storms can collide and combine, producing one awesome monster storm--is wrong. When two storms of approximately equal strength approach each other, they tend to rotate around a common center, then go their separate ways, in a process called the Fujiwara Effect. In rare cases they may merge into one storm, but the resulting storm will not be stronger than either of the original two storms, since wind shear from each storm will affect the other. More commonly, when two storms interact, one will destroy the other with its wind shear. This is what Hurricane Wilma did to Tropical Storm Alpha this year.

Jeff Masters

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Gamma Dying

By: JeffMasters, 8:51 AM GMT on 十一月 20, 2005

As per the latest NHC forecast track, it appears Gamma has been nothing but a tease. The system is barely holding on to its tropical storm status and is not expected to intensify any due to strong shear that is only expected to increase further. Deep convective has greatly diminished as per the lastest satellite imagery.
The official track of the system takes it very gradually east-northeast, and then curves it even further towards the east-southeast. It appears that no large landmasses will be effecting by the system as it moves through the Caribbean. Some areas of heavy rain can be expected, however, as local regions of deep convection persist.

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Gamma Position Adjusted

By: JeffMasters, 10:20 PM GMT on 十一月 19, 2005

Just a reminder, this is Shaun, not Dr. Masters.

Gamma Update

Well, some new developments have transpired since my last update. A hurricane hunter that investigated Gamma found that the center of the storm was considerably farther southeast than originally thought. You can see the storm center on the visible satellite loop spinning just north of the Honduras coast. While looking at this loop, you can see a very slight eastward movement which is expected to be short-lived.
The storm center is exposed to the south with the main convection field still observed well north of the center, which has a minimum low pressure of 1004 mb. Flight level winds were reported at 49 knots, with an initial intensity of 40 knots. The storm's convection also remains unorganized.
Gamma is faced with some obstacles with regards to intensification. Wind shear is still considerably strong over the system (20-30 kt of southwesterly vertical shear) and this value is expected to increase even more. This by itself should be enough to inhibit any significant strengthening. Secondly, the ridge of high pressure to the system's north is expected to weaken, allowing a trough and low pressure system to develop over the eastern United States. This should turn northeast and again hamper any significant intensification.
Models have once again trended more to the east and south and this is again reflected in the official NHC forecast track, which now takes it across central Cuba and well south of Florida towards the southern Bahamas. This track follows the GFDL closely with regards to position. The GFS loops a weak Gamma through the northwest Caribbean south of Cuba while the BAM takes the storm just south of Florida.
Also, the storm created landslides in Honduras today and claimed the lives of two people.

Figure 1. Most recent computer models for Gamma.

Figure 2. Official NHC forecast track taking Gamma even farther south that previous forecasts.

Updated: 10:22 PM GMT on 十一月 19, 2005

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Message from Jeff and Gamma Update

By: JeffMasters, 9:31 AM GMT on 十一月 19, 2005

Dr. Masters was nice enough to write you all a blog entry before he left for vacation. Enjoy what he wrote along with a Gamma Update below.

Message from Dr. Masters

It's probably premature to talk about this, since we may still see more tropical storms this season, but was this year's total of 24 Atlantic tropical storms really a record? It is almost certainly a record for the number of storms since the year 1944. That was the year that the U.S. began flying regular long-range aircraft reconnaissance missions over the Atlantic to detect tropical storms far out over the ocean. 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. Beginning 1960, weather satellites gave us full coverage of all the ocean areas, and it is unlikely we missed any tropical storms after then. Looking at the tracks for the 2005 hurricane season, only Tropical Storm Lee may have been short-lived enough to not be detected by aircraft and ships. Similar examinations of the hurricane tracks of storms from the past ten years yields an average of perhaps one storm per year that may have been missed. However, for the period 1851-1910, the Atlantic Hurricane Database Re-analysis Project estimates that the number of missed tropical storms and hurricanes for the 1851-85 era is on the order of 0-6 per year and on the order of 0-4 per year for the period of 1886 to 1910. (The higher detection for the latter period is due to increased ship traffic, larger populations along the coastlines and more meteorological measurements being taken.) There were no years in the the 1851-1885 period with more than 12 tropical storms. But 1887 had 19 tropical storms, so there is a small chance that 1887 tied 2005 with 23 storms if the maximum of four missed storms occurred.


Figure 1. Tracks for all 2005 Atlantic tropical cyclones.

During the 1910-1944 era, there is one other year that might have challenged 2005 for the record number of storms--1933, when 21 tropical storms formed. If we assume that increased ship traffic since the 1886-1910 era resulted in 0-3 tropical storms being missed during 1933, there is a 25% chance that 1933 bested 2005 for the busiest season on record, if a full three storms went undetected. Hurricanes are much harder to hide than tropical storms, though, since hurricanes last longer and typically have long tracks that multiple ships will encounter. Thus, it is likely that this year's tally of 13 hurricanes is unmatched since 1851. There were only 10 hurricanes in 1933, and 11 in 1887.

So in conclusion, the 23 storms and 13 hurricanes observed in 2005 were both very probably records for the post-1850 time period for the Atlantic. There may have been years before 1851 that had greater levels of activity, as the emerging science of paleotempestology is attempting to discover.

Jeff Masters

Gamma Update
Satellite imagery showed an increase in convection north of the storm's center early, but has since decreased once again. The storm center was located at 16.9N 86.2W at 1 a.m. EST with sustained winds at 45 mph. This is 140 miles east-southeast of Belize City.
High pressure north of the storm is expected to weaken, allowing a trough currently over the Plains to sweep the storm on a more northern course. Some strengthening of the system is possible, but wind shear is still high so any further intensification will be limited.

Figure 2. Computer models for Tropical Storm Gamma.
A couple of the (GFS and UKMET) are out to lunch, keeping the storm system in the western Caribbean and dissipating it. The latest run of the GFDL has trended more to the east, keeping the system's center off the Yucatan Peninsula, tracking it over western Cuba and through the Florida Straits. As far as Florida, this model run takes the storm farther south than the run earlier on Friday.
The NHC official forecast trends toward the GFL as the BAM model appears to be too far to the west, taking the storm over the Yucatan Peninsula.
Tropical Storm Warnings have been posted for the coast of Belize where heavy rainfall is also expected. Warnings are also in effect for the eastern coast of the Yucatan Peninsula and the Bay Islands of Honduras.

I will be back later Saturday with another update.

Updated: 9:36 AM GMT on 十一月 19, 2005

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Gamma has formed

By: JeffMasters, 10:28 PM GMT on 十一月 18, 2005

Hello everyone, it's Shaun again.

Gamma is here!

A hurricane hunter investigating the remnants of Twenty-seven discovered the system has re-organized into a broad area of low pressure. The aircraft also observed winds of 49 knots at 1500 feet along with a couple other areas of 45 knots winds north of the center. These two bits of information have lead to the issuing of advisories for Tropical Storm Gamma.

Gamma has formed in an area of strong wind shear (15-25 kt) and models forecast the wind shear to increase over the next few days.

Models handle the storm in very different ways. What the models do agree on is the strong high pressure north of Gamma is expected to weaken over the next few days. A trough is then expected to move into the Southeast. The official NHC forecast reflects the GFDL which turns the storm towards Florida. But it doesn't not represent the GFDL in some way as the GFDL takes the storm over the Yucatan Peninsula.

Some of the other models do not even strengthen the storm due to the high wind shear that is forecast, and the GFS takes it east across the Caribbean.

The moral of the story is that it is too early to tell what the storm is going to do. We will have to wait for a few more model runs to make a better guess.

I tend to be a little pessimistic on the intensity of these types of storms until some further development occurs, and you can definately see uncertainty in the NHC discussion.

Nonetheless, it is quite impressive to take a look at the GFDL in the long term to see the heck of a Nor-easter over the Northeast with the help of the remnants of Gamma.

Updated: 11:05 PM GMT on 十一月 18, 2005

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Disturbance in the Northwest Caribbean

By: JeffMasters, 7:21 PM GMT on 十一月 17, 2005

Hello all, it's Shaun again.

Disturbance in the northwest Caribbean

The National Hurricane Centered issued a Tropical Disturbance Statement for the disturbance in the northwest Caribbean Sea at 4:25 PM EST.
To summarize the statement, a hurricane hunter investigated the area and found that the disturbance off the Nicaragua coast had not developed into a tropical depression. In fact, areal coverage and intensity of shower activity has decreased significantly over the past few hours as evidence in satellite imagery.

The hurricane hunter also investigated the remnants of Tropical Depression Twenty-seven and found no closed circulation. Suprisingly, tropical storm force winds along with shower activity was observed in the area.
When looking at the satellite imagery, it is evident that there is significant convection noted along with the remnants of Twenty-seven. It seems as though this system now has the best chance of further development over the next few days as it resides in an environment of weak shear. The farther north it travels, however, the more shear it will encounter.

Updated: 10:17 PM GMT on 十一月 17, 2005

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Twenty-seven Dies, Stronger Low in the southwest Caribbean

By: JeffMasters, 8:12 PM GMT on 十一月 16, 2005

Hello all,
As Dr. Masters indicated in his last entry, he is on a well-deserved vacation for the next few days. This gives you all an opportunity to meet the rest of the meteorologists here at the Weather Underground. Over the next few days, you may hear from John Celenza, Elaine Yang, or Tim Roche. But for now, this is Shaun Tanner giving you a rundown on the tropics.

Tropical Depression Twenty-seven and other low:

Well, the depression lost its closed circulation as per the 10:00 a.m. EST update. The remnants of this system are not expected to organize further, but instead be absorbed by a developing system in the southwest Caribbean. In fact, the latest satellite images of the system show an arm of convection pulling away from the main convection area on the west side, possibility signaling the beginnings of the absorption process.
The low center associated with the absorbing system is located a few hundred miles east of the coast of Nicaragua as per the latest water vapor imagery. A large area of clouds and convection is noted throughout the western Caribbean and over Central America as the system
progressively moves west-northwestward. Upper-level winds are favorable for the system to develop into a tropical depression over the next 24 hours or so if the core remains over its essential warm water energy source. This is the big if. The GFDL is quite progressive in intensifying this system before its landfall over Nicaragua so it should be interesting to see what kind of development occurs. Whether or not this system develops further, the Central American coast from Panama to Honduras will continue to see very heavy rainfall from this system's convection. Mudslides are certainly possible in this region already drenched by the previous week's rains.
A hurricane hunter may investigate this developing system Thursday should it be warranted.

Updated: 10:23 PM GMT on 十一月 16, 2005

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TD 27 still hanging on

By: JeffMasters, 1:37 PM GMT on 十一月 15, 2005

Tropical Depression 27 continues to struggle against high wind shear generated by strong upper-level westerly winds. The storm has a small area of deep convection over the center, and a very small and weak circulation center. The circulation was too small to be resolved by the QuikSCAT satellite in its pass at 5:30 am this morning. Wind shear has held steady at about the same level we've seen the past two days, 20 knots. This shear is still high enough that there remains a 10% chance that the depression will dissipate within the next 24 hours. If the storm can survive until then, the shear will decrease enough to allow TD 27 to strengthen into a tropical storm and remain in a threat to the Caribbean for the rest of the week.

The eventual intensity of TD 27 is still highly uncertain. If TD 27 can position itself under an upper-level anticyclone that is expected to develop by Wednesday over the central Carribean, the storm has a chance to attain hurricane status. Ocean temperatures are 28-29C--plenty warm enough to allow a hurricane to form. However, the GFDL model is no longer predicting that this will be a major hurricane--it forecasts that TD 27 will strike Honduras as a Category 1 hurricane late in the week. This may be a result of the fact that the models are now forecasting increasing wind shear over the western Caribbean starting Friday. The other major intensity model, the SHIPS model, forecasts a strong tropical storm by the end of the week.

The computer models continue to agree that TD 27 will track westward over the Caribbean for the next five days, under the steering of a strong ridge of high pressure. By the end of the week, the storm should slow down, as a trough of low pressure to the north breaks down the ridge. This trough may be strong enough to force TD 27 northwards, where it would get caught in the westerly winds prevailing over Cuba and get recurved out to sea. This solution is favored by the Canadian model. The other models keep the ridge strong enough so that TD 27 remains over the ocean, or makes landfall in Honduras late in the week. I still believe Honduras is most at risk from this storm, followed by Nicaragua, Cuba, Jamaica, the Cayman Islands, and the Bahamas.

The Hurricane Hunters are scheduled to make their first flight into TD 27 this afternoon at about 2 pm EST.

This will be my final blog for nine days, I am headed to Puerto Rico for vacation. I hope not to be on the front lines for the next tropical system, but it certainly is possible! This hurricane season could well extend into early December, as happened in the 2003 hurricane season. I will be back to blogging on November 25 to talk about what remains of hurricane season, summarize this amazing Hurricane Season of 2005, and speculate on next year's hurricane season. Be sure to catch the PBS NOVA and Frontline shows on Hurricane Katrina, airing Tuesday Nov. 22 and 8 pm and 9 pm, I hope to talk about that show, as well.

While I am gone, meteorologists John Celenza and Shaun Tanner of the Weather Underground will be updating my blog on all the latest about TD 27.

Jeff Masters

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TD 27 still battling strong shear

By: JeffMasters, 9:36 PM GMT on 十一月 14, 2005

Wind shear from strong upper-level westerly winds has disrupted Tropical Depression 27 this afternoon. The depression was probably near tropical storm strength for a few hours late this morning, but since that time, the center of circulation has become more exposed, and the deep convection has retreated to the southeast side. The spiral band that had formed to the south is gone now. Wind shear is continuing to drop, and is now in the 15 - 20 knot range. This shear is still high enough that there remains a 10% the depression will dissipate within the next 48 hours. If the storm can survive until past then, the shear will decrease enough to allow TD 27 to strenghen into a tropical storm and remain in a threat to the Caribbean for the rest of the week.

The eventual intensity of TD 27 is highly uncertain, and will be highly dependent on the track of the storm. If TD 27 can position itself under an upper-level anticyclone that is expected to develop by Wednesday over the central Carribean, the storm has a chance to attain hurricane status. Ocean temperatures are 28-29C--plenty warm enough to allow a hurricane to form. The GFDL model still predicts TD 27 will intensify into a major Category 3 hurricane by the end of the week. However, the other major intensity model, the SHIPS model, forecasts a strong tropical storm by the end of the week. There is no way to tell now which model is more likely to be correct.

The computer models agree on the basic idea that TD 27 will track westward over the Caribbean for the next five days, under the steering of a strong ridge of high pressure. By the end of the week, the models begin to diverge.
The GFDL and NOGAPS depict a stronger system and show a threat to Jamaica, while the GFS and UKMET have a weaker system farther south that is more of a threat to Honduras and Nicaragua. None of the models show the storm moving far enough north to get caught in the westerly winds prevailing over Cuba and getting recurved out to sea. It appears that the ridge of high pressure steering TD 27 westwards will continue to hold in place for at least seven days, making Honduras the most at-risk area for a strike. Remember, a lot can change with forecasts for the large-scale weather patterns five to seven days from now, and the future track that far in advance will depend heaviy on how intense the storm becomes.

The Hurricane Hunters are scheduled to make their first flight into TD 27 Tuesday afternoon.

I'll be back with an update in the morning, unless TD 27 gets a name tonight. Incidently, TD 27 is only the 3rd tropical depression in history to form in November in the eastern Caribbean.

Jeff Masters

Updated: 9:39 PM GMT on 十一月 14, 2005

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Looks like Gamma is here

By: JeffMasters, 5:16 PM GMT on 十一月 14, 2005

Tropical Depression 27 has improved significantly in its appearance on visibile satellite imagery the past few hours, and it is very likely that this storm will be upgraded to Tropical Storm Gamma at 4 pm. The storm's deep convection has increased and now covers the circulation center, and an impressive spiral band has formed to the south. Satellite intensity estimates from The University of Wisconsin's CIMSS estimate that this is a 1000 mb tropical storm with 50 mph winds. Wind shear has dropped from 25 knots to about 20 knots this morning, which is still high enough to prevent anything more than slow strengthening. The remainder of this morning's discussion appears below, unchanged.

We've seen two systems in the past month, Wilma and Alpha, survive and even intensify in the face of high wind shear. TD 27 has already shown the ability to exist in a highly sheared environment, and I expect it will hold together long enough to take advantage of the lower wind shear expected to develop over the Carribean by Wednesday. The eventual intensity of TD 27 will be highly dependent on its track. If the storm stays in the northern portion of the Caribbean, where wind shear is strong, TD 27 will probably never strengthen to more than a tropical storm. However, if TD 27 can track further south through the southern Caribbean, wind shear is expected to be much lighter. Ocean temperatures are warm enough to allow a hurricane to form, and the GFDL model predicts TD 27 will intensify into a major Category 3 hurricane by the end of the week.

The computer models did not initialize TD 27 very well in their runs that we have available this morning, so our confidence in the long-term track of TD 27 is low. All the models agree on the basic idea that TD 27 will track westward over the Caribbean for the next five days, under the steering of a strong ridge of high pressure. By the end of the week, the models begin to diverge, with the GFS, NOGAPS, and GFDL models strengthening the ridge further, driving TD 27 into Nicaragua or Honduras. The UKMET and Canadian models disagree, and forecast that a trough of low pressure will turn TD 27 northwards in the vicinity of Jamaica and the Cayman Islands. TD 27 would then get caught in strong westerly winds, cross Cuba, then scoot through the Bahama Islands to the northeast. No model is indicating that TD 27 will threaten the U.S. mainland, and the storm would have to walk a very narrow tightrope to make it all the way to Florida. With such strong westerly winds blowing across Cuba and the Florida Straights, TD 27 will very quickly recurve away from the U.S. once it gets as far north as Jamaica's latitude.

The Hurricane Hunters are scheduled to make their first flight into TD 27 Tuesday afternoon.

I'll be back with an update late this afternoon when the 7am EST (12Z) model runs are available.

Jeff Masters

Updated: 5:27 PM GMT on 十一月 14, 2005

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TD 27 struggling

By: JeffMasters, 3:08 PM GMT on 十一月 14, 2005

Tropical Depression 27 formed last night from a tropical wave moving through the Lesser Antilles Islands, but is struggling to survive in the face of 20-25 knots of wind shear from strong upper-level westerly winds over the Caribbean. The storm's low-level circulation center is exposed, and the strong westerly winds are keeping what little deep convection the storm has, confined to its east side. This intensity and area coverage of the thunderstorms on the depression's east side has slowly increased this morning, but unless the shear relaxes and allows some deep convection to persist near the center, TD 27 will not be able to intensify much. Wind shear is expected to remain high today, and I give the shear a 10% chance of completely tearing the depression apart within the next 24 hours.

However, we've seen two systems in the past month, Wilma and Alpha, survive and even intensify in the face of high wind shear. TD 27 has already shown the ability to exist in a highly sheared environment, and I expect it will hold together long enough to take advantage of the lower wind shear expected to develop over the Carribean by Wednesday. The eventual intensity of TD 27 will be highly dependent on its track. If the storm stays in the northern portion of the Caribbean, where wind shear is strong, TD 27 will probably never strengthen to more than a tropical storm. However, if TD 27 can track further south through the southern Caribbean, wind shear is expected to be much lighter. Ocean temperatures are warm enough to allow a hurricane to form, and the GFDL model predicts TD 27 will intensify into a major Category 3 hurricane by the end of the week.

The computer models did not initialize TD 27 very well in their runs that we have available this morning, so our confidence in the long-term track of TD 27 is low. All the models agree on the basic idea that TD 27 will track westward over the Caribbean for the next five days, under the steering of a strong ridge of high pressure. By the end of the week, the models begin to diverge, with the GFS, NOGAPS, and GFDL models strengthening the ridge further, driving TD 27 into Nicaragua or Honduras. The UKMET and Canadian models disagree, and forecast that a trough of low pressure will turn TD 27 northwards in the vicinity of Jamaica and the Cayman Islands. TD 27 would then get caught in strong westerly winds, cross Cuba, then scoot through the Bahama Islands to the northeast. No model is indicating that TD 27 will threaten the U.S. mainland, and the storm would have to walk a very narrow tightrope to make it all the way to Florida. With such strong westerly winds blowing across Cuba and the Florida Straights, TD 27 will very quickly recurve away from the U.S. once it gets as far north as Jamaica's latitude.

The Hurricane Hunters are scheduled to make their first flight into TD 27 Tuesday afternoon.

I'll be back with an update late this afternoon when the 7am EST (12Z) model runs are available.

Jeff Masters

Updated: 3:10 PM GMT on 十一月 14, 2005

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TD 27 arrives

By: JeffMasters, 4:39 AM GMT on 十一月 14, 2005

After suffering through the made-for-TV movie "Category 7: End of the World" about meteorologically impossible storms that nearly destroy the world, I came back to the all-too-real world of the Hurricane Season of 2005, which I would have thought was a near impossibility had you told me before the season started what would transpire. Twenty-seven tropical cyclones? Unreal!

Tropical Depression 27 is very unimpressive tonight. Wind shear is still rather high right now, at 10 - 15 knots, and these hostile winds are keeping the area of deep convection around the storm small. The shear may even act to tear the storm apart Monday or Tuesday. TD 27 does have the potential to grow into a hurricane, and possibly a major hurricane, if it can survive the next two days and make it into the central Caribbean where the waters will be warmer and the wind shear lighter. I'll be back in the morning with a full analysis.

Jeff Masters

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New threat near Barbados; Panama disturbance fizzles

By: JeffMasters, 2:19 PM GMT on 十一月 13, 2005

The tropical disturbance that has festered over the waters between Panama and Nicaragua the past three days has dissipated, and tropical storm formation is no longer expected in this region.

A new area of disturbed weather has developed about 80 miles south of Barbados this morning. A low level circulation center is apparent near 12N 59W on both visible satellite imagery and an 8 am EDT QuikSCAT satellite pass. Deep convection associated with this 1007 mb low is mostly to its north, where the QuicSCAT satellite saw winds of up to 35 mph. Wind shear is quite high for tropical storm formation to occur, about 20 knots, but this shear is expected to decrease over the next few days. A tropical depression could form as early as Monday as the system crosses the Lesser Antilles islands into the eastern Caribbean. It is more likely, however, that development would occur Wednesday or later as the system moves into the central Caribbean.

The models are not gung-ho on this system, except for the Canadian model, which brings it quickly to hurricane strength just south of Hispanolia on Wednesday. The GFS model doesn't develop the system at all, and the other models forecast a weak tropical storm in the central Caribbean by Thursday.


Figure 1. Early model runs for the disturbance near Barbados.

I'll have an update Monday morning, or late tonight if the system develops.

Jeff Masters

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Panama disturbance weaker

By: JeffMasters, 5:05 PM GMT on 十一月 12, 2005

The rains have diminished over Panama today as the area of disturbed weather in the south-central Caribbean has weakened. The intensity and areal coverage of the disurbance has decreased since yesterday, although there are still some intense thunderstorms moving ashore along the Nicaraguan coast. Wind shear has increased from 15 to 20 knots since yesterday and contributed to the weakening.

Some slow development of this disturbance is still possible over the coming week, as wind shear values are expected to fall starting Monday. The UKMET and NOGAPS models are still showing a tropical storm forming between Nicaragua and Jamaica by Thursday, but the GFS model is no longer predicting this. The earliest a tropical depression would be likely to form is Tuesday. Friday or later is a more likely bet.


Figure 1. GFS model forecast five days from now, showing a tropical disturbance with copious rainfall (bright green and yellow colors) near Nicaragua. However, the GFS is no longer showing a closed isobar of surface pressure around the rain area, indicating that this is not forecast to be a tropical storm. Click here to see the full GFS forecast for rainfall and surface pressure for the coming 14 days in the Caribbean.

The rains should ease off in Panama and Costa Rica today, which have seen some impressive rainfall amounts the past three days. Some rainfall totals for the 72 hours ending at 7 pm Friday night:

Limon, Costa Rica: 210 mm (8.29 inches)
Jaque, Panama: 166 mm (6.54 inches)
El Porvenir, Panama: 151 mm (5.94 inches)

I'll be back with an update Sunday morning.

Jeff Masters

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No change to Panama disturbance

By: JeffMasters, 3:37 PM GMT on 十一月 11, 2005

The area of disturbed weather affecting Panama and the surrounding ocean waters has changed little since Thursday afternoon. The are several clusters of intense thunderstorms, and some upper level outflow to their north, but no circulation center evident. The cloud pattern looks disorganized. About 10 - 20 knots of shear covers the area, which should prevent much in the way of development today and Saturday. By Sunday, wind shear levels are expected to drop and continue falling over most of the Caribbean as the strong upper-level westerly winds relax and move further north. This may allow a tropical depression to form as early as Sunday. The GFS and NOGAPS models favor development off the coast of Nicaragua early in the week, while the UKMET and Canadian models favor development near Puerto Rico later in the week.


Figure 1. GFS model forecast five days from now, showing a tropical storm with copious rainfall (bright green colors) forming near Nicaragua.

It is highly uncertain what land areas might be at risk if development does occur. The primary areas at risk would be Nicaragua, Honduras, Cuba, Jamaica, the Cayman Islands, Hispanolia, and Puerto Rico.

Some rainfall totals for the 24 hours ending at 10 pm Thursday night:

Limon, Costa Rica: 59 mm (2.32 inches)
Santiago, Panama: 83 mm (3.27 inches)
El Porvenir, Panama: 103 mm (4.06 inches)

I'll be back with an update Saturday morning.

Jeff Masters

Updated: 3:39 PM GMT on 十一月 11, 2005

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Tropics heating up

By: JeffMasters, 11:00 PM GMT on 十一月 10, 2005

The persistent area of low pressure and storminess that has affected the ocean areas between Panama and Nicaragua has expanded today and become better organized. A weak circulation at mid levels of the atmosphere was evident on visible satellite imagery this afternoon, as was some upper-level outflow to the north. Intense thunderstorms now cover much of Panama and the surrounding ocean areas, and these storms will bring heavy rains to Panama and Costa Rica the next two days as they move westward at about 10 mph. Wind shear over the area is about 10 knots, which may allow some slow development over the next few days. The GFS computer model continues to show that early next week this area of disurbed weather may start to move slowly northward and develop into a tropical storm.


Figure 1. GFS model forecast seven days from now, showing a tropical storm with copious rainfall (bright green colors) forming in the south-central Caribbean Sea.

It is highly uncertain what land areas might be at risk if such a development does occur. The three main possibilities would be:

1) A track like Hurricane Beta into Nicaragua.

2) A track like Hurricane Michelle in 2001, which struck southern Cuba then passed northeastwards through the Bahamas.

3) A track like "Wrong-Way Lenny" of 1999, the only hurricane ever recorded that took an extended west-to-east path through the Caribbean.

Anything that works its way far enough north is going to get picked up and quickly recurved northeastward by one of the many troughs of low pressure migrating across North America. This means that except for a low threat to South Florida, the U.S. would not be at risk. Additionally, given that there has only ever been one storm knicknamed "Wrong-Way", the eastern Caribbean would probably not be at risk, either. I'll be able to spend my vacation in Puerto Rico next week at the beach, instead of taking shelter at the Internet Cafe and writing blog entries. The primary area at risk would be Nicaragua, Honduras, Cuba, Hispanolia, Jamaica, and the Cayman Islands.

I'll be back with an update tomorrow morning. Remember that the computer models are rather poor at forecasting tropical storm development, and nothing at all may develop next week. But given that this is the Hurricane Season of 2005, I'd give at least 50/50 odds we'll see a Tropical Storm Gamma by late next week in the central Caribbean.

Jeff Masters

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Tropical Storm Gamma next week?

By: JeffMasters, 2:57 PM GMT on 十一月 10, 2005

The tropics remain quiet today. Strong westerly winds blowing across the Caribbean are creating up to 80 knots of shear, making tropical storm development very unlikely for the next two or three days. However, all of the models are forecasting that these strong winds will relax and shear values will drop dramatically across the central Caribbean by Tuesday. The persistent area of low pressure and storminess that has affected the ocean areas between Panama and Nicaragua the past three weeks will expand. The GFS, NOGAPS, and UKMET models all indicate that a tropical storm may form in the south central Caribbean by the middle of next week.


Figure 1. GFS model forecast seven days from now, showing a tropical storm with copious rainfall (bright green colors) forming in the south-central Caribbean Sea.

It is highly uncertain what land areas might be at risk if such a development does occur. The three main possibilities would be:

1) A track like Hurricane Beta into Nicaragua.

2) A track like Hurricane Michelle in 2001, which struck southern Cuba then passed northeastwards through the Bahamas.

3) A track like "Wrong-Way Lenny" of 1999, the only hurricane ever recorded that took an extended west-to-east path through the Caribbean.

Anything that works its way far enough north is going to get picked up and quickly recurved northeastward by one of the many troughs of low pressure migrating across North America. This means that except for a low threat to South Florida, the U.S. would not be at risk. Additionally, given that there has only ever been one storm knicknamed "Wrong-Way", the eastern Caribbean would probably not be at risk, either. I'll be able to spend my vacation in Puerto Rico next week at the beach, instead of taking shelter at the Internet Cafe and writing blog entries. The primary area at risk would be Nicaragua, Honduras, Cuba, Hispanolia, Jamaica, and the Cayman Islands.

I'll be back with an update tomorrow morning. Remember that the computer models are rather poor at forecasting tropical storm development, and nothing at all may develop next week. But given that this is the Hurricane Season of 2005, I'd give at least 50/50 odds we'll see a Tropical Storm Gamma by late next week in the central Caribbean.

Jeff Masters

Updated: 3:45 PM GMT on 十一月 10, 2005

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This winter's forecast: NOAA vs. the woolly bears

By: JeffMasters, 4:32 PM GMT on 十一月 09, 2005

The tropics are quiet again today, so let's follow up on yesterday's discussion about the long range forecast for the coming United States winter. Those of you outside the U.S. will probably be more interested in what the International Research Institute for Climate Prediction has to say for your country, and I encourage you to check out their excellent web site for their seasonal forecasts. Interestingly, they forecast that virtually the entire world will have average to much above average temperatures during the December-February period, with only two tiny pockets of slightly below-average temperatures in Australia and central Asia. This should keep the oceans at the near-record high temperatures for near year's hurricane season, helping fuel another round of more intense than usual hurricanes. In addition, El Nino is expected to remain in a near-neutral phase the next 6-9 months (same as for this year's hurricane season), which should result in a higher than usual number of tropical storms and hurricanes for 2006. Still, I don't think we'll see anything like this year's level of activity, which was a once-in-a-lifetime hurricane season. Dr. Bill Gray's team at Colorado State University issues their first forecast for the 2006 hurricane season on Tuesday, December 6, and we'll talk more about next year's season then.

As we discussed yesterday, the official woolly bear caterpillar forecast for the U.S. mid-Atlantic coast area was for a warmer than average winter. The official NOAA 90-day forecast for the upcoming winter, issued on October 20 by the Climate Prediction Center (CPC), disagrees, calling for equal chances of an above average or below average winter over the eastern half of the country, but a higher than average chance of a warmer than average winter over the western half of the country. How well has the official forecast done in recent years? NOAA rates its forecasts using the Heidke skill score, which is a measure of how well a forecast did relative to a randomly selected forecast. A score of 0 means that the forecast did no better than what would be expected by chance. A score of 100 depicts a "perfect" forecast and a score of -50 depicts the "worst possible" forecast. For the 90-day temperature forecasts issued 1.5 months in advance done in January through May of this year, the Heidke skill score was greater than zero for two of the forecasts, less than zero two of the forecasts, and about zero the other forecast. The Heidke skill score for 90-day temperature forecasts issued 1.5 months in advance has averaged 8 the past ten years (see Figure 1.) So, while there is some skill in forecasting what the winter will be like 1.5 months in advance, this skill is not much better than flipping a coin or relying on woolly bear caterpillars. Let's look at some examples from forecasts for previous winters issued at about this time of year. The 90-day forecast done in mid-October of 1999 for the winter of 2000 was awesome, with a Heidke skill score of 50. However, the 90-day forecast done in mid-October of 2000 for the winter of 2001 was horrible, with a Heidke skill score of -15.


Figure 1. Skill of the official 90-day forecasts issued 1.5 months in advance by NOAA's Climate Prediction Center. Note that the average skill is positive, but has remained flat the past ten years, indicating that our skill in making long-range forecasts has not improved.

Why do seasonal forecasts do so poorly? It's partially because our physical understanding of what controls the climate is so poor. It's also in large part due to the fact that the long-term weather is chaotic and fundamentally unpredictable by nature, and no amount of physical understanding will help us. So, pick your forecast: woolly bear, coin flip, NOAA--the three techniques have similar levels of accuracy. Or you can check out the predictions of Psychic Helane, who wrote me to say she had correctly forecast the impact of Hurricane Wilma on South Florida over one month in advance. Her winter prediction calls for "the north especially St. Paul, Minnesota and Upstate NY will see its worst winter in memory." If I were an energy futures trader, I would wait until I saw a longer track record for Helane's weather predictions. She is also calling for a "huge hurricane in Alabama" this month, which is a virtual impossibility, given that sea surface temperatures in the Gulf of Mexico are now less than 80F (26.5C), which is too cold to support a major hurricane. Go with the official NOAA forecasts, which a have a proven track record of some having a least a little skill compared to chance.

Jeff Masters

Winter Weather

Updated: 7:15 PM GMT on 一月 05, 2012

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Forecast for the winter of 2005-2006:: Part I, the woolly bears

By: JeffMasters, 1:52 PM GMT on 十一月 08, 2005

And now for something completely different: the woolly bear caterpillar forecast for the coming winter. After months of focusing on the death and destruction wrought by the fury of nature's hurricanes, and now tornadoes, it's time to take a break. The tropics remain quiet again today, allowing us to indulge. The political discussions can wait until another day.

According to legend, the severity of the upcoming winter can be judged by examining the pattern of brown and black stripes on woolly bear caterpillars--the larvae of Isabella tiger moths. If the brown stripe between the two black stripes is thick, the winter will be a mild one. A narrow brown stripe portends a long, cold winter.

The Hagerstown, Maryland Town and Country Almanack has been publishing weather forecasts and weather lore for 209 years. The Almanack sponsors an annual woolly bear caterpillar event, where local school children in Hagerstown collect woolly bears. A panel of judges examines the collected specimens and issues a woolly bear forecast for the upcoming winter. Gerald W. Spessard, the Town and Country Almanack's business manager and one of this year's two judges, observed that the middle brown stripes on the 20 caterpillars collected this year were thicker than usual. "There's not a whole lot of black at either end, so we both agree this should be a fairly mild winter," Spessard said, according to an AP press release.

Naturally, this forecast only applies to the Hagerstown, Maryland area, so other locales will need to do their own woolly bear work to gauge the local winter forecast. The Hagerstown critters have had mixed success the past three years with their forecasts--they've been correct about half the time. This is only slightly worse than the official NOAA long range forecasts.

Several scientific studies have been done on woolly bear caterpillar forecasts, including one by the American Museum of Natural History. None of these studies have shown any correlation between woolly bear markings and the severity of the upcoming winter. According to Ned Rozell, science writer at the University of Alaska's Geophysical Institute, Biologist Dr. Charles Curran began studying woolly bear markings and the severity of winters in 1948. For the first three years, the caterpillars had wide brown bands, correctly forecasting three consecutive mild winters. The caterpillars failed the next year, and Dr. Curran gave up the study in 1955 after finding two groups of caterpillars living near each other that had vastly different predictions for the upcoming winter.

So, you're probably better off using the official NOAA long-range forecast for the upcoming winter--although not by much. I'll discuss the official NOAA forecast for the upcoming winter tomorrow, and talk about how well they've done in past years.

Jeff Masters

Winter Weather

Updated: 7:15 PM GMT on 一月 05, 2012

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Fall tornado rips Indiana

By: JeffMasters, 5:01 PM GMT on 十一月 07, 2005

An rare November tornado killed 22 and injured over 200 as it ripped through mobile home park near Evansville, Indiana at 2 am Sunday morning. A preliminary damage survey of the tornado indicates that it was an F3 on the Fujita damage scale. Winds in an F3 tornado range from 158 mph to 206 mph. The tornado was 1500 feet wide, and had a 15-20 mile long damage path. The squall line of supercell thunderstorms that spawned the tornado was very low-topped, with echo tops of only 10-15 thousand feet. More typically, severe thunderstorm echo tops reach 40,000 feet. Forward motion of the line was exceptionally fast, estimated at 70 to 75 mph.

A separate strong F2 tornado touched down in central Kentucky in Munfordville. This tornado had a 200 yard wide path and traveled one mile through the center of Munfordville, causing significant damage to roofs in the downtown area. No injuries or deaths occurred with this tornado. A third tornado, also rated at F2 with 140 mph winds, touched down in Kentucky about 50 miles southwest of Evansville, Indiana. This tornado injured five as it cut a 150 yard wide, 11-mile long swath of damage.


Figure 1. Damage to a mobile home park near Evansville, Indiana. Image credit: Paducah, KY NWS.

Tornado outbreaks in the Fall are uncommon compared to the Spring in the Midwestern United States. The most recent Fall tornado to affect the Midwest occurred when an F4 tornado struck Ohio near the Indiana border on November 10, 2003, killing four and injuring 26. One might expect Fall to have a similar level of tornado activity compared to Spring, since strong cold air masses interact with warm, humid air masses in both seasons. However, there are important differences between the seasons. For example, the amount of sunlight is much lower in the Fall, when we are approaching the annual minima of sunlight on the December 21 Winter Solstice. With autumn's longer nights, morning temperatures are usually cooler than in Spring. This cooling causes more atmospheric inversions, where the temperature at the surface is cooler than it is aloft. This increases the stability of an air mass, and stable air is a strong deterrent to storm formation. Of the 25 most deadly tornadoes to affect the U.S., only one has occurred in the Fall.


Figure 2. The annual cycle of tornado activity for southern Indiana shows strong peak in Spring, and just a slight peak late in the Fall. Image credit: NOAA Storm Prediction Center.

Jeff Masters

Tornado

Updated: 6:53 PM GMT on 一月 05, 2012

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Indiana tornado

By: JeffMasters, 7:15 PM GMT on 十一月 06, 2005

The tropics are quiet today, but tornado alley in the Midwestern U.S. saw its worst tornado in 7 years last night when a 3/4 mile wide tornado cut a 20-mile long swath of damage just north of Evansville, Indiana. Tornado warnings were issued 30 minutes in advance, but many of the 22 people who died probably never heard the sirens, which hit at 2 am local time. Near-record warm temperatures helped fuel the line of thunderstorms that spawned the tornado. The high temperature in Evansville was 77 F yesterday, 1 degree shy of the record. The temperature was still 70 at 1 am, shortly before the tornado hit.

2005 has seen tornado activity about 10% below average, according to statistics compiled by the Storm Prediction Center. In fact, May of 2005 was the first May since record keeping began that the state of Oklahoma saw no tornadoes. But this morning's Evansville tornado was the most deadly in the U.S. since the Oak Grove, Alabama tornado of April 8, 1998 killed 32. This morning's tornado brings this year's tornado death toll to 32, which is still well below the average of 46 tornado deaths for a typical year.

Jeff Masters

Tornado

Updated: 6:53 PM GMT on 一月 05, 2012

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Tropics quieting down

By: JeffMasters, 4:27 PM GMT on 十一月 05, 2005

An area of disturbed weather continues over the southwestern Caribbean off of the coast of Nicaragua. Both the intensity and the areal coverage of the thunderstorms in this area have decreased since yesterday, and the amount of rain drenching Central America has lessened. Some observed rain amounts for the 24 hours anding at 7 pm EST Friday:

Puerto Lempira, Honduras 44 mm (1.7")
Puerto Cabezas, Nicaragua 83 mm (3.3")
Puerto Obaldia, Panama 78 mm (3.1")
El Porvenir, Panama 98 mm (3.9")

The disturbed area of weather should persist for at least two more days and continue to bring 1-3 inches of rain per day to these regions. However, tropical storm formation is looking more unlikely, due to higher amounts of wind shear. The GFS model continues to show a steady increase in wind shear over most of the Caribbean Sea during the coming week. It would be foolish to declare that this portends an end to the Hurricane Season of 2005, but odds are growing increasingly long that we'll see another tropical storm.

Jeff Masters

Updated: 4:32 PM GMT on 十一月 05, 2005

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Southwestern Caribbean remains disturbed

By: JeffMasters, 3:25 PM GMT on 十一月 04, 2005

The rains continue over Honduras, Nicaragua, Panama, and Costa Rica today in association with a disturbed area of weather that has persisted all week. The focus today has shifted away from the northern coast of Honduras eastwards, to the ocean areas east of Nicaragua that spawned Hurricane Beta. Wind shear is in the 5-10 knot range over this area, which may allow for some slow tropical development the next few days. Steering currents are pushing things westward at about 10 mph. If a tropical depression does form in this area, it would primarily be a threat to Nicaragua and Honduras.

Some rainfall amounts for the three-day period ending at 7 pm EST Thursday night include:

La Ceiba, Honduras 107 mm (4.2")
Guanaja, Honduras 132 mm (5.2")
Roatan, Honduras 136 mm (5.4")
Puerto Cabezas, Nicaragua 59 mm (2.3")
Bocas del Toro, Panama 200 mm (7.9")

There may be some respite from the rains on the north coast of Honduras for the Roatan area today, but the areas of Nicaragua and northeast Honduras hardest hit by Hurricane Beta will continue to suffer periods of heavy rain. This disturbed weather pattern is expected to continue for at least the next four days, seriously aggravating Beta's flooding situation. By the middle of next week, the GFS model is indicating strong westerly winds will invade the Caribbean, creating enough wind shear to put an end to the tropical storm formation threat and reduce the heavy rains over Central America. However, some of the other computer models disagree with this scenario, and maintain the threat of tropical storm formation in the area north of Panama. In any case, the tropical storm threat to the U.S. for the next seven days is very low.

I'll update the situation over the weekend as important changes occur.

Jeff Masters

Updated: 3:28 PM GMT on 十一月 04, 2005

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Western Caribbean development

By: JeffMasters, 2:51 PM GMT on 十一月 03, 2005

An intense area of deep convection has developed off the northeast coast of Honduras this morning. This area has some impressive cold cloud-top temperatures and the beginnings of some upper level outflow to the north. Wind shear is about 10 knots over the area, which may allow some slow development as the disturbance moves west along the northern coast of Honduras over the next day or so. The disturbance is probably too close to land to allow development into a tropical depression, and the wind shear is not forecasted to drop any further. However, this disturbance will bring very heavy rains to northeast Honduras today. This area is still reeling from the heavy rains from Hurricane Beta that washed out bridges and cut roads. Thousands of people are still in shelters in this area, which is cut off from the rest of the country. Fortunately, no deaths or injuries have been attributed to Hurricane Beta's floods and winds.

Jeff Masters

Updated: 2:56 PM GMT on 十一月 03, 2005

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NWS politics

By: JeffMasters, 2:08 PM GMT on 十一月 02, 2005

The tropics look to be quiet this week, so I will discuss some of the political issues going on with the National Weather Service that deserve attention.

Today is the last day for the public to comment on NOAA's proposed changes to its Policy on Partnerships in the Provision of Environmental Information. For those of you who wish to comment on the proposed change, you can click here.

NOAA proposes to change Section 4 to read as follows:

4. The nation benefits from government information disseminated both by Federal agencies and by diverse nonfederal parties, including commercial and not-for-profit entities. NOAA recognizes the government best serves the public interest by cooperating with private sector and academic and research entities to meet the varied needs of specific individuals, organizations, and economic entities. NOAA will take advantage of existing capabilities and services of commercial and academic sectors to avoid duplication and competition in areas not related to the NOAA mission. NOAA will give due consideration to these abilities and consider the effects of its decisions on the activities of these entities, in accordance with its responsibilities as an agency of the U.S. Government, to serve the public interest and advance the nation's environmental information enterprise as a whole.

For comparison, the present Section 4 reads as follows:

4. NOAA recognizes the public interest is served by the ability of private sector entities and the academic and research community to provide diverse services to meet the varied needs of specific individuals, organizations, and economic entities. The nation benefits from government information disseminated both by Federal agencies and by diverse nonfederal parties, including commercial and not-for-profit entities. NOAA will give due consideration to these abilities, and consider the effects of its decisions on the activities of these entities, in accordance with its responsibilities as an agency of the U.S. Government, to serve the public interest and advance the nation's environmental information enterprise as a whole.

I've been too busy with hurricane season to do much research on the ramifications of this change. Wunderblogger Skyepony has set up a disscussion page about this issue, though. I did contact an official at the National Weather Service Employees Organization (NWSEO) last week to ask what he thought the greatest threats facing the NWS were, and he did not mention this issue at all. The top issue in his mind was the proposed budget cuts coming for NWS, which I will discuss later this week. I also asked about the the National Weather Service Duties Act of 2005, Senate Bill S.786, introduced April 14 by Sen. Rick Santorum, R-Pa. This bill would make it illegal for the National Weather Service (NWS) to issue non-severe weather forecasts, should a company in the private sector be able to provide them and lodge a formal request with the Secretary of Commerce for the NWS to stop issuing the products. The Santorum bill was of little concern to the NWSEO, he indicated, since there is no interest in the Senate subcommittee where the bill sits in pursuing it, and the bill still has no co-sponsor. Santorum has been quiet about the bill of late, and this bill's unpopularity has done him harm in the re-election campaign he is currently losing in Pennsylvania. My April blog discussing the matter can be found here.

Assuming the tropics stay quiet, I'll be back tomorrow to talk about the upcoming NWS budget cuts or the new NWS gag order issued after Katrina.

Jeff Masters


Politics

Updated: 7:55 PM GMT on 十月 24, 2011

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November hurricane outlook

By: JeffMasters, 2:14 PM GMT on 十一月 01, 2005

November is here. What kind of activity can we expect this month from the busiest hurricane season on record? Historically, only about 5% of all Atlantic tropical storm activity occurs after November 1. Between 1871 and 2004, 57 tropical storms have formed in November. Of these, 28 became hurricanes, and four of these, major hurricanes. So on average, one tropical storm forms in November every other year, and we can expect a November hurricane about one year in four. Given that this is no ordinary year, the chances of getting a November storm are much higher than average. The Caribbean continues to be dominated by a deep layer of winds from the east from the surface to the upper Troposphere, conditions that mean low wind shear and a favorable environment for tropical storm formation. This deep easterly flow is forecast to continue for at least the next week, so we will have to watch all the tropical disturbances that may form in the Caribbean. There is a tropical disturbance just south of Hispanolia to watch today, but this disturbance is struggling with a lot of dry air being wrapped into it by an upper-level low pressure system just west of Hispanolia, and no tropical storm formation is likely through tomorrow in the Atlantic.

Farther north, in the Gulf of Mexico and Bahamas, strong westerly winds characteristic of the typical Fall weather regime over North America have settled in, making tropical storm formation unlikely in this area. As we can see from Figure 1 below, the central and southern Caribbean are the primary breeding grounds for November tropical cyclones in the Atlantic. Here, the ocean temperatures remain warmest the longest. The typical way a tropical storm develops in November is that a cold front pushes off the coast of North America, and its tail end remains over the southwest Caribbean. The remains of the cold front have a little bit of spin, and this area festers over the warm Caribbean waters for three to five days, and finally organizes into a tropical storm.


Figure 1. Preferred formation area and tracks for November tropical cyclones.

Historical November tropical cyclones
The most extraordinary November hurricanes was "Wrong-Way Lenny", which affected the northern Leeward Islands as a strong Category 4 hurricane with peak winds of 155 mph on November 17-18, 1999. Lenny was the first storm to have an extended west-to-east track across the central and eastern Caribbean Sea in the 135-year Atlantic tropical cyclone record, and was the strongest November hurricane on record. Hurricane Gordon was the deadliest November hurricane. It claimed 1122 lives in Haiti when it passed just west of the country as a tropical storm on November 13, 1994. Lenny claimed six lives in Costa Rica, five in the Dominican Republic, two in Jamaica, two in Cuba, and eight in Florida. Property damage to the United States was estimated at $400 million (1994 dollars), and was severe in Haiti and Cuba as well.

Three November hurricanes have hit the U.S.--an unnamed 1916 Category 1 hurricane that hit the Florida Keys, an unnamed 1925 Category 1 hurricane that struck Sarasota, Florida, and Hurricane Kate, which struck the Florida Panhandle on November 22, 1985.

Jeff Masters

Updated: 2:16 PM GMT on 十一月 01, 2005

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About

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

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