Category 6™

Hurricane season of 2008 draws to a close

By: JeffMasters, 12:38 AM GMT on November 26, 2008

The hurricane season of 2008 draws to a close on Sunday, but leaves behind an indelible mark in history and in the lives of the millions of people it affected. After two years of relative tranquility, the active hurricane period that began in 1995 returned in full force this year, living up to pre-season predictions. It was a top ten hurricane season when considering the total number of named storms and major hurricanes, and ranked 24th using a better measure of total seasonal activity, the Accumulated Cyclone Energy (ACE). Hurricane records in the Atlantic go back to 1851. An ACE index of 95-100 is average, so this year's ACE of 141 puts this season at about 45% more active than average. The remainder of this post will list some notable statistics, records, and events that occurred during the hurricane season of 2008. It is by no means an exhaustive list, and I could have added much more.

First, here's how this season measured up to other seasons:

6th most named storms (16; the record is 28 in 2005)
25th most hurricanes (8; the record is 15 in 2005)
9th most major hurricanes (5; the record is 8 in 1950)
24th highest ACE index (141; the record is 250 in 2005)
13th highest Named Storm Days (84.75; record is 136 in 1933)
40th highest Hurricane Days (29.5; the record is 62.5 in 1995)
28th highest Major Hurricane Days (8.5; the record is 24.5 in 1961)



Notable records for 2008
-Fourth costliest hurricane season on record ($21 billion dollars in U.S. damage, according to ISO's Property Claim Services)
-First time major hurricanes have been observed in five separate months (Bertha, Gustav, Ike, Omar, Paloma occurred in July, August, September, October, and November, respectively)
-First time six consecutive storms made U.S. landfall (Dolly, Edouard, Fay, Gustav, Hanna, and Ike).
-First time three major hurricanes have hit Cuba (Gustav, Ike, Paloma)
-Costliest hurricane in Texas history (Ike, $16.2 billion)
-Second deadliest U.S. hurricane since 1972, and 26th deadliest in history (Ike, with 82 dead)
-Highest wind gust ever measured in a hurricane over land (Gustav, 212 mph in Pinar del Rio, Cuba)
-First storm ever to make four landfalls in one state (Fay, in Florida)
-Second strongest November hurricane (Paloma, 145 mph winds)
-Smallest tropical cyclone on record (Marco)
-Longest-lived July hurricane on record, longest-lived hurricane so early in the season, longest-lived tropical storm in July and so early in the season (Bertha, which was a hurricane 7.75 days, eclipsing the previous record of 7 days held by Hurricane Emily of 2005. Bertha was at tropical storm strength for 17.25 days).
-Farthest east forming tropical storm and hurricane for so early in the season (Bertha)

Haiti's misery
Nowhere was the hurricane season of 2008 more terrible than in Haiti. Four storms--Fay, Gustav, Hanna, and Ike--dumped heavy rains on the impoverished nation. The rugged hillsides, stripped bare of 98% of their forest cover thanks to deforestation, let flood waters rampage into large areas of the country. Particularly hard-hit was Gonaives, the fourth largest city. According to reliefweb.org, Haiti suffered 793 killed, with 310 missing and another 593 injured. The hurricanes destroyed 22,702 homes and damaged another 84,625. About 800,000 people were affected--8% of Haiti's total population. The flood wiped out much of Haiti's crops, and aid workers are concerned that spiraling food costs will add to the toll of 26 children that died of malnutrition in recent weeks. For those looking to help out, I recommend an end-of the-year donation to the Lambi Fund of Haiti. I've been impressed with their efforts over the years to effect change at a grass-roots level, with an emphasis on reforestation efforts.

Cuba's ordeal
Three major hurricanes hit Cuba, the first time on record that has happened. Hurricanes Gustav, Ike, and Paloma killed eight people on the island, and caused a combined $10 billion in damage. Some 4.4 million people had to be evacuated for the three hurricanes, 2.8 million of these because of Ike. Ike and Gustav destroyed 63,000 homes and damaged 440,000 more, and every province of Cuba reported hurricane damage. According to the official Granma newspaper, "the economic, social, and housing situation of the country has been devastated as never before in its history" due to Gustav and Ike.


Figure 1. Hurricane Gustav at 12:05 pm EDT 8/30/2008, as viewed by NASA's Terra satellite. At the time, Gustav was a Category 4 hurricane with 150 mph winds. Image credit: NASA.

Texas suffers Ike's massive storm surge
Hurricane Ike, though just a Category 2 hurricane at landfall, brought Texas' second highest storm surge on record--17.48 feet to inland Chambers County. Ike's highest surge at the coast was 16.8 feet on the west side of Galveston Bay at the town of Bayside Terrace (Figure 2). The highest high water mark from Ike was an towering 21.2 feet in Texas City. This high water mark was due to the combined action of the surge plus waves on top. The record highest storm surge for a Texas hurricane still belongs to Category 4 Hurricane Carla of 1961, with 22.8 feet measured at Port Lavaca. It is likely that the Great Galveston Hurricane of 1900 and another Category 4 Galveston hurricane in 1915 had higher storm surges in Galveston Bay than Hurricane Ike did.


Figure 2. High still water marks (in feet) from Hurricane Ike in Harris County. Image credit: FEMA and National Weather Service.

Ike makes a direct hit on the Turks and Caicos Islands
Hurricane Ike pounded the Turks and Caicos Islands as a Category 4 hurricane with 135 mph winds. Ike made direct hits on Grand Turk Island, South Caicos Island, and Great Inagua Island. About 95% of all buildings on these islands were damaged or destroyed, and Ike was the strongest hurricane on record in this region. The only other major hurricane to hit Great Inagua Island was a 1899 Category 3 storm. Grand Turk and South Caicos Island have had major hurricane strikes in 1893, 1866, and 1945.


Figure 3. Microwave image of Hurricane Ike as it made landfall on Great Inagua Island at 7:45 am EDT 09/07/2008. The storm had formed concentric eyewalls at the time. Image credit: Navy Research Lab, Monterey.

New Orleans is battered by Gustav, but the levees hold
Hurricane Gustav ripped into Louisiana just west of New Orleans on September 1 as a strong Category 2 hurricane with 110 mph winds. Gustav killed 43 people in the U.S. and did $3.8 billion in damage, making it the 20th costliest hurricane on record in the U.S. Storm surge heights up to 12.5 feet were recorded in the New Orleans area. Surge heights were similar to, and in some cases higher, than those measured during Hurricane Katrina along the New Orleans levee system. Thankfully, the levee system withstood Gustav's test.

Fay eases drought conditions in Florida and the Southeast U.S.
A two-year drought in Central Florida that brought Lake Okeechobee to critically low water levels was effectively ended by Tropical Storm Fay in August. Fay's rains of 10-15 inches increased the level of Lake Okeechobee from 11 feet to 15 feet, putting it near average levels. Fay also dropped up to ten inches of rain across parched regions of the Southeast U.S., reducing their drought level from exceptional to extreme (Figure 4). Fay also killed eleven people in the U.S. and did approximately $180 million in damage.


Figure 4. Total rainfall from Tropical Storm Fay over the U.S. Image credit: NOAA.

Paloma ravages Cayman Brac Island
Paloma roared through the Cayman Islands as a Category 4 hurricane with 140 mph winds, brushing Grand Cayman Island, but pounding the "Sister Islands" to the northeast--Little Cayman and Cayman Brac--with its northern eyewall. The hardest-hit Cayman island was Cayman Brac, population 2,000. Damage on Cayman Brac was very heavy, with over 90% of all the buildings damaged. Paloma was the worst hurricane to hit the island since the deadly 1932 hurricane that flattened Cayman Brac, killing 69 people. Ironically, both hurricanes occurred on November 8. Due to the angle Paloma hit the island at, only an 8-foot storm surge was repported. The 1932 hurricane reputedly carried a 24-foot storm surge.


Figure 5. Damage on Cayman Brac from Hurricane Paloma. Image credit: Mangroveman.

The Portlight Charity mobilizes to help Gulf Coast hurricane victims
A group of Weather Underground bloggers mobilized to bring aid to the underserved and disabled victims of the Hurricane Ike disaster under the banner of the Portlight.org charity. It was great to see our community come together to help out those devastated by one of the most damaging hurricanes of all time. The emergence of Portlight from our community of Internet weather enthusiasts is truly a unique and remarkable event. I look forward to helping Portlight make a difference in many hurricane seasons to come, and hope you will consider making a year-end donation to help out.

Happy Thanksgiving!
The travel weather looks good for the U.S. for this holiday weekend, and I'll be joining the traffic chaos Wednesday morning. I'm headed to Puerto Rico's Vieques Island with my family, and will be back to blogging on December 3. Have a great holiday, everyone!

Jeff Masters

Winter forecast, part III: the Old Farmer's Almanac

By: JeffMasters, 2:23 PM GMT on November 24, 2008

Since 1792, the Old Farmer's Almanac has been issuing long-range seasonal weather forecasts. This year, the Almanac is predicting that winter will be colder than average for 3/4 of the U.S., and above average over just 1/8 of the country. Only the Pacific Northwest and the upper Midwest near Minnesota are predicted to be warmer than average. For the Appalachian region that includes the three woolly bear forecasts I discussed last week, the Old Farmer's Almanac is siding with Oil Valley Vick and Kelly the woolly bear, forecasting colder than average temperatures. The Hagerstown Woolly Bears and NOAA disagree, predicting warmer than average temperatures are more likely.

How accurate is the Old Farmer's Almanac?
The Old Farmer's Almanac claims to have a secret formula developed in 1792 based on sunspots and climatology, which gives their long-range predictions 80% accuracy. I've heard a number of anecdotal stories about how uncannily accurate their forecasts are, and have always felt a vague sort of anxiety that maybe I should be checking them out when someone asks me what the upcoming winter will be like. However, the Almanac does not post any verification statistics of their forecasts. It is not hard to do a simple check of their forecast accuracy, though. Unfortunately, the results of my check and those done by several others show that there is little reason to believe that the Old Farmer's Almanac forecasts are any better than flipping a coin.


Figure 1. Observed departure of temperature from average for the period Nov. 2004-Mar. 2005. Superimposed in bold text is the winter forecast made in the 2004 Old Farmer's Almanac for the same period. The Almanac got four regions correct and eight incorrect, with two too close to call.

For example, for the winter of 2004-2005 (Figure 1), the November 2004 version of the Old Farmer's Almanac made a simple prediction of "cold" or "mild" for sixteen separate regions of the U.S. The original forecast map they presented only labels the U.S. in fourteen places, and I've overlaid these predictions on a temperature anomaly map showing what actually happened during the winter of 2004-2005. If we assume that "mild" refers to an above average temperature forecast and "cold" refers to a below average temperature forecast, then the Almanac got four regions correct, eight wrong, with two too close to call. Admittedly, I've "eyeballed" this, and it is a subjective verification. Still, I don't see any way that this forecast could approach even 50% (chance) accuracy. Their precipitation forecast fared better, with seven correct regions, five incorrect, and two too close to call. I also looked at the Farmer's Almanac forecasts for the winter of 2006-2007. They did much worse that winter, with only three of sixteen temperature forecasts verifying, and five out of twelve precipitation forecasts verifying (four were too close to call). For these two winters, the Old Farmer's Almanac made a successful forecast just 37% of the time.

Studies by Jan Null
Jan Null, a meteorologist who founded the private weather consulting firm, Golden Gate Weather in California, has evaluated the Old Farmer's Almanac predictions for San Francisco for three separate years. His first study looked at the forecasts for 1999-2000. His conclusion: "Even trying to be objective and giving the benefit of the doubt to cases that were close, I found last year's forecast from the Old Farmer's 2000 Almanac for San Francisco to be laughable at best and abysmal at worst. The Old Farmer's Almanac was wrong on their monthly temperature forecast 8 out of the 12 months (67%) and wrong on their rainfall forecast 5 of the 8 months evaluated (63%)". His grade for the Old Farmer's Almanac winter forecast for San Francisco during 2006-2007 was a D+. He also evaluated the Old Farmer's Almanac for two separate summers and winters for all sixteen regions of the U.S., and found mostly poor results. For the summer of 2005, just one of the sixteen Old Farmer's Almanac regional forecasts got both the temperature and the precipitation correct. He plans to post a verification of their 2008 summer forecast sometime in the next week.

Weatherwise magazine study
In the October 1981 issue of Weatherwise magazine, pages 212-215, John E. Walsh and David Allen performed a check on the accuracy of 60 monthly forecasts of temperature and precipitation from the Old Farmer's Almanac at 32 stations in the U.S. They found that 50.7% of the monthly temperature forecasts and 51.9% of the precipitation forecasts verified with the correct sign. This compares with the 50% success rate expected by chance.

Old Farmer's Almanac climate forecast
It's also of interest to note that the Old Farmer's Almanac believes that sunspot cycles and other factors suggest that "a cold, not warm climate may be in our future". Their climate forecaster is Joeseph D'Aleo, who was the first Director of Meteorology at the Weather Channel. Mr. D'Aleo is now retired, and is often quoted for his skeptical opinions about climate change.

Conclusion
The results of my forecast verifications and those done by several others indicate that there is little reason to believe the Old Farmer's Almanac claim of 80% accuracy. These verifications attempted to be fair, but one can justifiably argue they were not objective nor complete. However, unless the Almanac posts some scientific evidence to the contrary, I won't believe their forecasts are any better than flipping a coin. One's best bet for the upcoming winter forecast is to use NOAA's prediction, which calls for an an above-average chance of a warm winter across the center portion of the U.S. If you live in Banner Elk, North Carolina, it might be wise to go with Kelly the Woolly worm's forecast of a cold winter, though, given the success of her predecessors!

Tropical disturbance near Costa Rica
An area of disturbed weather (96L) has developed in the extreme southern Caribbean, near the coast of Costa Rica. Wind shear is a hefty 20-30 knots over the disturbance, which will keep any development slow. The disturbance will bring heavy rains to Costa Rica and Nicaragua through Wednesday. If the center can stay off shore, this disturbance has the potential to develop into a tropical depression. NHC is giving a moderate (20-50% chance) that 96L will develop into a tropical depression by Wednesday morning. The GFDL model does develop 96L, but none of the other models do. I'll have an update on the system this afternoon if it gets more organized.

Jeff Masters

Winter Weather

Winter forecast, part II: NOAA's predicts a warm winter for the Central U.S.

By: JeffMasters, 2:51 PM GMT on November 21, 2008

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.

The official National Oceanic and Atmospheric Administration (NOAA) 90-day forecast for the upcoming winter, issued on November 20 by their Climate Prediction Center (CPC), calls for above average temperatures across the Central U.S. and Alaska. The remainder of the country has equal chances of above or below average temperatures. A dryer than average winter is expected over much of the Southern U.S., including the drought-stricken Southeast U.S.


Figure 1. Temperature forecast for the upcoming winter--December, January, and February 2009--made by NOAA's Climate Prediction Center. No areas of the country ar forecast to have an above-average chance of being colder than normal, but the Central U.S. has up to a 50% chance of having above-average temperatures.

How are the NOAA winter forecasts made?
NOAA uses several tools to make their forecasts. One key tool is their Climate Forecast System (CFS) model. This model includes a version of the GFS forecast model that we use for everyday weather and hurricane track forecasts. The CFS model also includes an ocean model that interacts with the atmospheric model. These models solve mathematical equations of fluid flow using a supercomputer for the entire globe, on a 100-km grid. NOAA also uses statistical models, which look at past winters and see how they depended on quantities such as sea surface temperature anomalies. Temperature trends are important, too--if it has been warmer than average the last ten years, it's a good idea to forecast a warmer than average winter.


Figure 2. Skill of the official 90-day forecasts issued 0.5 months in advance by NOAA's Climate Prediction Center. Note that the average skill over the past ten years is not very high (9 on a scale of 0 to 100), and has remained flat, indicating that our skill in making long-range forecasts has not improved.

How good are the NOAA winter forecasts?
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 90-day temperature forecasts issued 0.5 months in advance, NOAA has averaged a 9 out of 100 on the Heidke scale since 1995 (Figure 2). So, while there is some skill in forecasting what winter temperatures will be like, this skill is not much better than flipping a coin. Depressingly, Heidke skill scores for three-month precipitation forecasts are even worse, averaging just a one on a scale of 1 to 100 over the past 15 years.

Let's look at some examples. Last's year's winter temperature forecast issued in mid-November did poorly (Figure 3), failing to forecast that the U.S. would have equal areas with both above and below average temperatures. The 90-day forecast done in mid-November of 2005 for the winter of 2005-2006 was awesome, with a Heidke skill score of 45. However, the 90-day forecast done in mid-November of 2006 for the winter of 2006-2007 had virtually no skill, with a Heidke skill score of one.



Figure 3. Temperature forecast for Dec 2007-Feb 2008 issued by NOAA's Climate Prediction Center on November 15, 2007 (top). They predicted Equal Chances (EC) of either above or below-average temperatures for the Northwestern U.S. (white colored areas), and a 30-60% chance of above average temperatures over most of the remainder of the country. In reality, the U.S. experienced an average winter, with approximately equal areas of the country receiving above and below average temperatures (bottom). Image credit: National Climatic Data Center.

Why do seasonal forecasts do so poorly? Primarily, it's because the long-term weather patterns are chaotic and fundamentally unpredictable. To a lesser degree, we are limited by our imperfect physical understanding of what controls the climate, and our imperfect computer models we use to simulate the climate. As computer power continues to increase and our models include better representations of the weather and climate at finer grid sizes, I anticipate that seasonal forecasts will improve. However, given that long-range forecasts have not improved since 1995 despite a large increase in computer power, I doubt that this improvement will be more than 10-20% over the next thirty years.

Seasonal forecast models vs. climate models
A common complaint one hears about global warming predictions made by climate models is, "How can we trust the predictions of these climate modes, when they so such a lousy job with seasonal forecasts?" It's a good question, and there is no doubt that seasonal forecasts have pretty marginal skill. However, there is a fundamental difference between making a seasonal forecast and making a 100-year climate forecast. A seasonal or a short-term weather forecast is what mathematicians call an "initial value" problem. One starts with a set of initial meteorological and oceanographic values that specify the initial state of the planet's weather, then solve the equations of fluid flow to arrive at the state of the atmosphere a few days, weeks, or months into the future. This forecast is highly sensitive to any imperfections one has in the initial conditions. Since there are large regions of the atmosphere and ocean we don't sample, it's guaranteed that the prediction will suffer significantly from imperfect initial conditions. Furthermore, the chaotic and turbulent nature of the atmosphere leads to many "bumps" in the weather pattern over time scales of days, weeks, and months. The nature of turbulence makes it impossible to accurately forecast these "bumps" that are superimposed on the mean state of the climate.

A 100-year climate forecast, on the other hand, is what mathematicians call a "boundary value" problem. Given an initial and final set of factors (called "forcings") that influence the climate, one runs a climate model 100 years into the future. The final state of the climate will depend on the strength of the forcings supplied. This type of model is not very sensitive to initial conditions, and is not trying to forecast the "bumps" of chaotic, turbulent atmospheric motion superimposed on the mean climate. Rather, one is trying to forecast the mean climate. As computer power increases and our physical understanding of how the climate works grows, these type of models will continue to significantly improve. While climate models do fail to properly simulate important aspects of our past climate, such as the Arctic warming of the 1930s, and the observed 0.1°C global temperature increase that occurs at the peak of the 11-year solar sunspot cycle, they have been very successful at simulating things like the global cooling triggered by the 1992 Mt. Pinatubo eruption, and the observed pattern of greatest global warming in the Arctic. I believe that climate models are already significantly more reliable than seasonal forecast models, and should continue to improve steadily in coming years.

Support the Portlight Christmas for Gulf Coast Kids Honor Walk
Saturday is the portlight.org Christmas for Gulf Coast Kids Honor Walk. This is a fundraiser to buy gifts for the kids along the Gulf Coast who might not have much in their stockings this year because of the ravages of Hurricane Ike. Our own StormJunkie will be walking up the Arthur Ravenel Jr. Bridge in Charleston, SC, and will be taking his webcam along. Tune in to the webcam site at 2:30 pm EST to follow the walk, and participate in a live chat. Sponsorships of any amount, small or large, are appreciated! The cam will go active about an hour before the walk. It should be a cold but beautiful day.

Jeff Masters

Winter Weather

Winter forecast, part I: the woolley bear prediction

By: JeffMasters, 1:48 PM GMT on November 20, 2008

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 on either end of the caterpillar is thick, the winter will be a mild one. A narrow brown stripe portends a long, cold winter. Some traditional forecasters say that the 13 segments on the caterpillar's body correspond to the 13 weeks of winter.

The Hagerstown, Maryland woolley bear forecast
The Hagerstown, Maryland Town and Country Almanack has been publishing weather forecasts and weather lore for 211 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. The results of this year's contest, which ended October 31: "From the small number of woolly bears, the consensus is that the winter will be very mild. The woolly bears predicted this by their three (3) bands of which the front band (representing the first half of winter and black in color) was shorter in length and normal. The back band (representing the second half of winter) was very small, thus indicating the mild winter prediction. As a result of those markings, which were similar in all woolly bears, the sponsors were able to make the predictions."

Oil Valley Vick
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. In Oil City, Pennsylvania, just 150 miles northwest of Hagerstown, organizers of the Pumkin Bumkin Festival have located the lair of "Oil Valley Vick", a woolly bear caterpillar of unknown forecasting ability, but great potential. In his inaugural forecast on October 23 this year, Oil Valley Vick wowed the crowd at the Pumkin Bumkin Festival when he crawled out of his log. The black stripes covering fully 2/3 of Oil Valley Vick's body left no doubt that he expected a cold, severe winter for northwestern Pennsylvania.


Figure 1. Kelly the woolly bear caterpillar with her owner, six-year-old Kurstin Hartsell of Ansonville, NC. Image credit: Jim Morton, Avery County Chamber of Commerce.

The Banner Elk, North Carolina Woolly Bear forecast
In Banner Elk, NC it's the fastest woolly bear caterpillar which is judged to be the best forecaster. After successfully out-sprinting hundreds of other woolly bears, this year's winner of the 31st Annual Woolly Worm Festival race was Kelly the Woolly Worm, raced by six-year-old Kurstin Hartsell of Ansonville, NC. Kelly the Woolly Worm's official forecast for the winter of 2008-2009 calls for the first four weeks to be cold and snowy, followed by three weeks of seasonably cold weather, followed by six weeks of snowy and cold weather (severely cold in week 11, March 1-7). A study of the predictions of the Banner Elk woolly bears between 1978 and 2000 revealed that "woolly worm winter predictions were exactly on target eight times out of 23, or 34.8%. Woolly worm predictions were close (4.0-4.9) another five times (21.7%). Woolly worm predictions were right in some areas, wrong in others (3.0-3.9) six times (26.1%). Woolly worm predictions were wrong more than they were right (2.0-2.9) four times (17.4%). Put another way, the woolly worms were close or completely right 57% of the time, and more than half right 82.6% of the time".

Other studies of woolly bear forecast accuracy
Several scientific studies have been done on woolly bear caterpillar forecasts, including one by the American Museum of Natural History. None of these studies has shown any correlation between woolly bear markings and the severity of the upcoming winter. According to the Old Farmer's Almanac, Dr. Charles Curran, curator of insects at the American Museum of Natural History in New York City, studied woolly bear markings between 1948-1956 in Bear Mountain State Park, 40 miles north of New York City. He found some preliminary results that seemed to indicate that the thickness of the bands might indicate the severity of the upcoming winter. However, 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, according to science writer Ned Rozell.

So, two out of three woolley bear forecasts point to a colder than average winter for the Appalachian region of the U.S. In upcoming blog posts, I'll analyze what NOAA's computer models and the Old Farmer's Almanac have to say about the upcoming winter.

Portlight making keynote presentation at charity funding conference today
The Portlight.org charity is making the keynote presenation at a funding conference hosted by a coalition of state and federal agencies which work in the area of post-disaster relief involving people with disabilities. The presentation is this morning, November 20, at 9:15 am EST. You can follow the proceedings via the portlight webcam at stormjunkie.com. At the conference, they plan to discuss the Hurricane Ike relief efforts made possible by the Weather Underground community. Thanks for everyone's support for making all this possible!

Jeff Masters

Winter Weather

Unexpected ocean cooling result found to be an error; 2nd warmest October on record

By: JeffMasters, 3:16 PM GMT on November 19, 2008

Since the publication in 2006 of the paper, Recent cooling of the upper ocean, climate scientists have been scratching their heads, trying to figure out why the upper layer of the ocean had cooled from 2004-2006. Since the oceans absorb more than 80% of the heat from global warming, we should expect to see the oceans heating up if the globe is warming. Climate skeptics pointed to the result as evidence that the planet was not warming after all, although surface and satellite measurements showed that the year 2005 was the warmest or second warmest year on record for the surface of the globe.

Now, the explanation for this apparent cooling of the oceans has been resolved--key measurements made by submersible robot buoys and that indicated the ocean was cooling were found to be in error. The new, corrected data show that no cooling of the oceans occurred in 2004-2006, in agreement with what the climate models were predicting. People often malign the accuracy of climate models, but sometimes they are more trustworthy than the data! The full story of the global ocean cooling mistake is presented in an excellent NASA article that I highly recommend reading. It gives a great picture of how science moves forward to correct mistakes.


Figure 1. Ocean temperature change from 2004 to 2006 originally showed drops of over 1.5° C in the Atlantic Ocean (top). The apparent large drop in temperature was due to bad data from buoys, and it disappeared when errors in these data sets were corrected (bottom). The remaining large swings in temperature visible in these maps are due to shifting positions of ocean currents. (Maps by Robert Simmon, based on data from Josh Willis and John Lyman.)

Second warmest October on record for the globe
The planet continues to stay extremely warm this year, though no record warm months have been recorded in 2008. October 2008 came the closest--it was the 2nd warmest October for the the globe on record, according to statistics released yesterday by the National Climatic Data Center. These statistics have been corrected for a widely reported error that was discovered earlier this month. Over land areas, October 2008 was the warmest October on record. The period January through October was the 9th warmest such period on record. Records extend back 129 years, to 1880. Much of the unusual warmth occurred over Asia, Australia, and Eastern Europe (Figure 2). According to the Australian Bureau of Meteorology, October 2008 was an exceptionally dry month in central and southeastern Australia, ranking as the driest October on record for South Australia, second driest for Tasmania, and third driest for Victoria.


Figure 2. Departure of temperature from average for October 2008. Image credit: National Climatic Data Center.

For the contiguous U.S., October was pretty ordinary. It was the 44th coolest and 51st driest October since 1895. October was the 7th wettest on record for the West North Central U.S. and the 17th driest for the Northwest U.S.

October 2008 Northern Hemisphere sea ice extent was the third lowest on record for the month of October, 34% below the mean from 1979-2000, according to the National Snow and Ice Data Center. This is 9.5% below the 1979-2000 average. The record October low was set in 2007.

There is neither a La Niña nor El Niño at present, and neutral conditions now prevail in the tropical Eastern Pacific. There is no indication that this will change in coming months, and most of the computer climate models forecast a continuation of neutral conditions over the next three months.

Portlight making keynote presentation at charity funding conference
The Portlight.org charity is making the keynote presenation at a funding conference hosted by a coalition of state and federal agencies which work in the area of post-disaster relief involving people with disabilities. The presentation is Thursday morning, November 20, at 9:15 am EST. You can follow the proceedings via the portlight webcam at stormjunkie.com. The webcam will also be running most of the day today as Stormjunkie and Presslord drive up to Atlanta for the conference, and host a Q and A session from their hotel room tonight. At the conference Thursday morning, they plan to discuss the Hurricane Ike relief efforts made possible by the Weather Underground community. Thanks for everyone's support for making all this possible!

I'll have a new blog post Thursday.

Jeff Masters

Climate Change

Santa Ana winds ease over Los Angeles

By: JeffMasters, 2:17 PM GMT on November 17, 2008

The Santa Ana winds have died down over Los Angeles, and winds should remain below 25 mph today through Thursday over the region. This should allow fire fighters to gain control of the three major blazes burning near the city. Wind gusts in excess of hurricane force--74 mph--were recorded at several mountain locations Friday and Saturday, thanks to the major difference in pressure between a strong high pressure system to the northeast of Los Angeles and lower pressure air over the ocean. By 4 pm PST Sunday, though, winds had fallen below 15 mph over the entire region (Figure 1), and a weak sea breeze had formed near the coast. Taking a look at this morning's wundermap (with fire layer turned on) for Los Angeles, we can see that winds are below 5 mph over the region. All high wind warnings and fire weather warnings have been canceled for California, but continued hot and dry conditions will slow down efforts of fire fighters to control the fires. The smoke has caused pollution problems in the city, and the Air Quality Index (AQI) for particulate matter less than 2.5 microns (PM2.5) exceeded the EPA standard yesterday. Today's pollution forecast calls for PM2.5 levels in the unhealthy for sensitive groups level, in excess of the EPA standards.


Figure 1. Wundermap (with fire layer turned on) for Los Angeles, California, at 4 pm EST Sunday November 16, 2008. Two major fires, the Sylmar fire to the north, and the Freeway fire to the east, are shown. The black colors show the relative concentration of smoke. The colored circles show the temperature, and the lines going into the circles show the direction the wind is blowing from. The perpendicular lines at the the end of these lines show how strong the wind is blowing. Each longer line is an additional 10 mph, and each shorter perpendicular line is an additional 5 mph. Thus, for the circle at upper right with a 66° temperature, the wind was blowing 15 mph out of the NNE. (Note that we've changed the convention used on marine maps, where these so-called "wind barbs" denote the winds in knots, not mph).

High temperature records
The hot flow of air off the desert set numerous high temperature records across Southern California on Sunday. Records set or tied included 88° in downtown Los Angeles, 93° in Camalillo; 86° at LAX airport; 90° at Long Beach; 89° at Paso Robles; 87° at Santa Maria; 91° at Woodland Hills; 87° at UCLA; 93° at Oxnard; and 87° at Santa Barbara. On Saturday, 30 high temperature records were set or tied across the state of California, including a blistering 93° in downtown Los Angeles (old record, 90° in 1936). The hottest new record was 94° at the Santa Ana Fire Station.

The forecast
Hot and dry conditions will persist over Los Angeles today, then gradually cool Tuesday and Wednesday. On Wednesday and Thursday, winds should reverse and blow cool, moist air from the oceans over the city, allowing fire fighters to gain full control of the fires. By Saturday, the GFS model is indicating a possible return to Santa Ana wind conditions for the weekend, but the ECMWF model disagrees. At this point, it appears we may get a weak Santa Ana wind event this weekend, but nowhere near as strong as the one that just ended.


Figure 2. Visible satellite image from NASA's Terra satellite taken on Sunday, November 16, 2008 at 11:30 am PST. Smoke from the Sylmar fire 20 miles north of Los Angeles has drifted out over the Catalina Islands, joined by a larger plume of smoke from the "Freeway Fire" in Orange County.

Support the Portlight Christmas for Gulf Coast Kids Honor Walk
The Portlight.org charity is sponsoring a new nationwide grassroots event to raise funds for and awareness of their ongoing efforts, specifically to provide Christmas presents (and maybe a big party) for kids and families in the Gulf Coast areas devastated by Hurricane Ike. They need 100 people across the country to commit to walking one mile this Saturday, November 22, and to raise at least $300.00 in sponsorship from friends, family, co-workers, neighbors, etc. Participants can choose where they want to walk--the local park, the mall, anywhere. Please support this worthwhile effort!

Jeff Masters

Fire

Fierce Santa Ana winds continue to fan Southern California fires

By: JeffMasters, 4:25 PM GMT on November 15, 2008

A strong Santa Ana wind event continues over Southern California, fanning two major fires that have caused over $100 million in damage near Los Angeles. Wind gusts up to 76 mph were clocked early this morning at Camp Nine near the Sylmar fire, which is burning in the mountains about twenty miles north of downtown Los Angeles. Yesterday, winds gusted to 72 mph near the Montecito Hills fire in Santa Barbara County. A Fire Weather Warning continues for the Los Angeles area, and high wind warning for winds of 25 to 45 mph with gusts to 60 mph have been posted for surrounding mountain areas. A strong high pressure system has built in to the north and east, and the clockwise flow of air around this high pressure system will drive strong east-to-west offshore winds from the mountains to the ocean over the Los Angeles metropolitan area through Sunday morning. As air drops out of the mountains, it will warm due to compression as its pressure increases. The warm winds have caused several record highs to be set, including 91° in Burbank yesterday. Very low humidities in the 5-10% range have contributed to the dangerous fire conditions. Fire conditions will ease on Sunday as high pressure weakens, allowing winds to slow down. However, winds are not forecast to reverse direction and blow moist air inland from the ocean until Tuesday.


Figure 1. Visible satellite image from NASA's Terra satellite taken on Saturday, November 15, 2008 at 10:45 am PST. Smoke from the Sylmar fire 20 miles north of Los Angeles has drifted out over the Catalina Islands. A smaller plume of smoke from the "Freeway Fire" in Orange County is also visible.

Tropical update
In the tropics, there are no threat areas to discuss, and none of the reliable models are calling for tropical storm formation over the next seven days. However, it is possible that an extratropical low expected to form south of the Azores Islands on Monday will be able to gradually acquire tropical characteristics during the week, and could become a subtropical storm late next week. Such a storm is not likely to threaten any land areas.

Jeff Masters

Fire

Santa Ana winds fan damaging Califonia fire; Bahamas disturbance 95L fizzles

By: JeffMasters, 1:52 PM GMT on November 14, 2008

A small area of surface low pressure (95L) is about 200 miles north of Puerto Rico, and is headed west at 10-15 mph. The disturbance has lost most of its heavy thunderstorm activity over the past 12 hours, thanks to an intrusion of dry air. There is a moderate level of wind shear (15-20 knots) over 95L, but this morning's QuikSCAT pass showed no evidence of a surface circulation, and only a slight wind shift.

Wind shear is forecast to remain in the moderate range, 15-20 knots, over the next two days, as the disturbance heads west. Since water temperatures are a warm 28°C, this may allow some slow development, if the disturbance can avoid ingesting more dry air. Dry air is plentiful on 95L's west side. The disturbance may bring heavy rain to the Bahamas Friday night through Saturday night, but this is not guaranteed, due to the large amount of dry air the storm must overcome. By Saturday afternoon, as 95L approaches the central Bahamas, an approaching trough of low pressure should turn the disturbance sharply northward and northeastward. I'm not expecting 95L to affect Florida's weather this weekend. The National Hurricane Center is giving 95L a low (<20% chance) of developing into a tropical depression by Sunday morning. High wind shear should tear the disturbance apart on Sunday.


Figure 1.Latest satellite image of disturbance 95L.

Southern California Santa Ana winds fan damaging fire
A moderate to strong Santa Ana wind event began last night in Southern California, and will continue through Saturday night. Wind gusts up to 72 mph were clocked this morning in Montecito Hills in Santa Barbara County, fanning a fire that destroyed 80 homes and injured four people. A Fire Weather Warning has been posted for the Los Angeles area, and high wind warnings for winds of 25 to 45 mph with gusts to 65 mph have been posted for surrounding mountain areas. A strong high pressure system has built in to the north and east, and the clockwise flow of air around this high pressure system will drive strong east-to-west offshore winds from the mountains to the ocean over the Los Angeles and San Diego metropolitan areas through Saturday. As air drops out of the mountains, it will warm due to compression as its pressure increases, leading to very warm temperatures 10-20 degrees above average. Adding to the fire danger will be the very low humidities of this desert air, in the 15-25% range. Fire conditions will ease on Sunday as high pressure weakens, allowing winds to slow down and eventually shift so that they blow moisture from the ocean over Southern California.

I'll have an update this weekend if conditions warrant. Upcoming blogs for next week include a quick summary of this year's hurricane season, a look at the 212 mph wind gust recorded on Cuba during Hurricane Gustav, and the forecast for the upcoming winter.

Jeff Masters

Fire

Disturbance 95L will bring heavy rains to the Bahamas Friday

By: JeffMasters, 9:54 PM GMT on November 13, 2008

A small area of surface low pressure (95L) is 300 miles northeast of Puerto Rico and headed is west at 10-15 mph. The disturbance in under a moderate level of wind shear (15-20 knots), and recent visible satellite imagery (Figure 1) shows a modest amount of heavy thunderstorm activity that is poorly organized and is not changing much in coverage or intensity. There is no surface circulation apparent on satellite imagery, but there has been a slight increase in the organization of the cloud pattern in the past few hours.

Wind shear is forecast to remain in the moderate range, 15-20 knots, over the next two days, as the disturbance heads west. Since water temperatures are a warm 28°C, this should allow some slow development. The central Bahamas can expect some heavy thunderstorms and gusty 25-30 mph winds Friday afternoon through Saturday from 95L. By Saturday afternoon, as 95L approaches the western Bahamas, an approaching trough of low pressure should turn the disturbance sharply northward and northeastward. I'm not expecting 95L to move over Florida, though Florida's east coast may catch the outermost thunderstorms of the disturbance on Saturday evening. High wind shear should tear the disturbance apart on Sunday. The National Hurricane Center is giving a medium (20-50% chance) that 95L will develop into a tropical depression by Saturday afternoon. I put the odds at the lower end of this spectrum, 20-30%.


Figure 1.Latest satellite image of disturbance 95L.

I'll have an update Friday morning.

Jeff Masters

Tropical Atlantic quiet; Southern California fire event possible Friday

By: JeffMasters, 2:26 PM GMT on November 12, 2008

The remains of Hurricane Paloma continue to spin over the Caribbean waters just south of Cuba, but wind shear is a high 30 knots, and there is virtually no chance that Paloma will regenerate. Elsewhere in the tropical Atlantic, there are no threat areas to discuss, and none of our reliable models are predicting tropical storm formation over the next seven days. There is an extratropical low pressure system that is expected to separate from the jet stream in the middle Atlantic just south of the Azores Islands 5-7 days from now, and it is possible this low could gradually acquire some tropical characteristics and become a subtropical storm late next week as it wanders over the open Atlantic Ocean. Such a storm would only be a threat to shipping interests, and I am not expecting any more tropical storms this season that will threaten land areas. With wind shear expected to rise over the Caribbean later this week, and continue to remain at high levels until late November, it is likely that the Atlantic hurricane season of 2008 is finally over in the Caribbean.

Paloma clean-up continues
The recovery effort from Hurricane Paloma continues in the Cayman Islands and Cuba. Paloma roared through the Cayman Islands Friday night and Saturday morning as a Category 4 hurricane with 140 mph winds, brushing Grand Cayman Island, but pounding the "Sister Islands" to the northeast--Little Cayman and Cayman Brac--with its northern eyewall. The hardest-hit Cayman island was Cayman Brac, population 2,000. About half of the island's population is homeless, and 95% of the structures on the island are damaged and 30% missing their roofs. The Cayman Compass reports that electricity is still out to most of the island, though Internet and cell phone service have been restored. Damage was also very heavy on Little Cayman Island, which suffered damage to approximately 90% of its buildings.

In Cuba, leader Raul Castro said yesterday that Cuba had suffered at least $10 billion in damage from Hurricanes Ike, Gustav, and Paloma. Paloma was the least damaging of the three, accounting for $1.4 billion of the damage total. This year was the first time on record that three major hurricanes have hit Cuba.


Figure 1. Hurricane Paloma near maximum intensity at 1:35 pm EST November 8, 2008. At the time, Paloma was a Category 4 hurricane with 140-145 mph winds. Image credit: NASA Earth Observatory.

Southern California fire event possible this week
A moderate to strong Santa Ana wind event is shaping up for Southern California Friday and Saturday, as high pressure builds in to the north and east. The clockwise flow of air around this high pressure system will drive strong east-to-west offshore winds from the mountains to the ocean over the Los Angeles and San Diego metropolitan areas. A Fire Weather Watch has already been posted for the mountain regions near Los Angeles, where wind gusts up to 60 mph are expected Friday and Saturday. Very windy, dry, and hot conditions are expected Friday and Saturday over Southern California, and the San Diego area will see near record temperatures 10 to 20 degrees above average.

Jeff Masters

Fire

Paloma dies; Cayman Brac and Cuba hard-hit

By: JeffMasters, 3:18 PM GMT on November 10, 2008

Hurricane Paloma has died, torn apart by high wind shear and passage over the rugged terrain of Cuba. The remains of Paloma can still be seen in satellite imagery, spinning over central Cuba, but with wind shear a hefty 50 knots, there is no chance of Paloma regenerating into a tropical storm. Elsewhere in the Atlantic, there are no threat areas to discuss, and none of the reliable computer models are forecasting tropical storm development over the next seven days. With wind shear expected to rise over the Caribbean later this week, and continue to remain at high levels until late November, it is likely that the Atlantic hurricane season of 2008 is finally over. It is possible we could get one more weak tropical storm out in the middle Atlantic, forming from an extratropical storm that gets cut off from the jet stream. Such storms are usually only a threat to shipping, and rarely affect land areas, though.

Paloma's impact on the Cayman Islands
Paloma roared through the Cayman Islands Friday night and Saturday morning as a Category 4 hurricane with 140 mph winds, brushing Grand Cayman Island, but pounding the "Sister Islands" to the northeast--Little Cayman and Cayman Brac--with its northern eyewall. The hardest-hit Cayman island was Cayman Brac, population 2,000, which was the only Cayman island to receive a direct hit from Paloma. Damage on Cayman Brac was very heavy, with over 90% of all the buildings damaged. However, the Cayman Compass reports that relief efforts are progressing swiftly. The airport has reopened, most of the roads have been cleared, and both gas stations on the island have re-opened. One person on the island sustained injuries requiring hospitalization. Paloma was the worst hurricane to hit the island since the deadly 1932 hurricane that flattened Cayman Brac, killing 69 people. Ironically, both hurricanes occurred on November 8.


Figure 1. Damage on Cayman Brac from Hurricane Paloma. Image credit: Glenda Davidowski.

Paloma's impact on Cuba
Paloma smashed into Cuba near Santa Cruz del Sur as a Category 3 hurricane with 120-125 mph winds. The hurricane destroyed at least 435 buildings in the city, and damaged 4,000 more. The hurricane's storm surge, estimated at over 20 feet, penetrated as far as a mile inland. However, no deaths have been reported in Cuba from Paloma, thanks to the evacuation of over 1.2 million people from vulnerable areas. The last major hurricane to hit Santa Cruz del Sur, the infamous Category 4 November 1932 hurricane, completely inundated the city with its storm surge, killing over 3,000 people. Paloma was the third major hurricane to hit Cuba this year, the first time that nation has received three major hurricane strikes. The other two major hurricanes, Gustav and Ike, did a combined $9.4 billion in damage to Cuba, destroying about 1/3 of the nation's crops. Paloma weakened so rapidly that its damage will be far less than Gustav's and Ike's. Seven Cubans died in Ike, and none in Gustav. The fact that only seven deaths occurred from the three major hurricane that hit Cuba this year is a testament to the success of their remarkable hurricane civil defense efforts. Some 4.4 million people had to be evacuated for the three hurricanes, 2.8 million of these because of Ike. Ike and Gustav destroyed 63,000 homes and damaged 440,000 more, and every province of Cuba reported hurricane damage. According to the official Granma newspaper, "the economic, social, and housing situation of the country has been devastated as never before in its history" due to Gustav and Ike.


Figure 1. Map of the hurricanes that have affected Cuba this year. Image credit: ReliefWeb.

Support the Portlight Christmas for Gulf Coast Kids Honor Walk
The Portlight.org charity is sponsoring a new nationwide grassroots event to raise funds for and awareness of their ongoing efforts, specifically to provide Christmas presents (and maybe a big party) for kids and families in the Gulf Coast areas devastated by Hurricane Ike. They need 100 people across the country to commit to walking one mile on November 22, and to raise at least $300.00 in sponsorship from friends, family, co-workers, neighbors, etc. Participants can choose where they want to walk--the local park, the mall, anywhere. Please support this worthwhile effort!

I'll have an update Tuesday.

Jeff Masters

Category 4 Paloma pounds the Cayman Islands, heads to Cuba

By: JeffMasters, 4:07 PM GMT on November 08, 2008

Hurricane Paloma exploded into a extremely dangerous Category 4 hurricane with 140 mph winds last night as it hammered the Cayman Islands. Paloma now ranks as the second most powerful November hurricane on record, and stands poised to deliver Cuba a devastating blow tonight. The latest data from the Hurricane Hunters and satellites indicate that Paloma has probably peaked in strength, and will slowly weaken today. Visible satellite loops show that strong upper-level winds from the west are starting to restrict the upper-level outflow on the west side of the storm, though the hurricane still has impressive organization and a well-formed eye. Infrared satellite loops show that the hurricane's cloud tops are warming, indicating weakening. The latest Hurricane Hunter mission departed the storm at 6:30 am EST, and the next mission should arrive about 1 pm EST. Radar from Camaguey, Cuba shows no evidence that the shear has weakened the eyewall of Paloma. There is evidence to suggest the hurricane may be forming a concentric eyewall, which would act to spread the hurricane's winds over a larger area and increase the region affected by a high storm surge.

Paloma's impact on the Cayman Islands
A strong trough of low pressure over the U.S. East Coast began pulling Paloma to the northeast late last night. Paloma's turn to the northeast came earlier than originally forecast, much to the advantage of Grand Cayman Island, but much to the detriment of Little Cayman and Cayman Brac islands. The earlier turn also allowed Paloma to stay just south of the higher levels of wind shear that would have weakened the hurricane. The eye of Paloma passed just east of Grand Cayman, and the strongest eyewall winds barely missed the island. Winds at the Grand Cayman airport on the west end of the island peaked out at 46 mph gusting to 62 mph at 7 pm EST, though winds were close to hurricane force on the east end of the island. Preliminary news reports indicate that the island suffered some flooding, but no major wind damage or storm surge.

Little Cayman and Cayman Brac were not so lucky. There are reports of heavy damage on the islands, which received a long battering by the northern eyewall of Paloma. Cayman Brac, which lies a little farther south than Little Cayman, took a direct hit, with the calm of the eye lasting several hours. Ironically, today is the anniversary of the deadly 1932 hurricane that flattened Cayman Brac, killing 69 people.


Figure 1. Visible satellite image of Paloma at 9 am EST Saturday November 8, 2008. Image credit: NASA/GSFC.

The forecast
A strong trough of low pressure over the U.S. East Coast is pulling Paloma to the northeast, and this trough should continue to pull the storm across Cuba tonight and into the Bahama Islands on Sunday. Wind shear is a high 25 knots, and is expected to increase to 35 knots tonight and 45 knots on Sunday. Paloma should not be able to intensify any further under this kind of shear, though it may be able to hold on to its current intensity until tonight, since it will take some time for the increasing shear to be able to penetrate into the heart of such a powerful, well-formed vortex and disrupt it. Landfall tonight in Cuba as a Category 3 hurricane with 115 mph winds is a good bet, which is the forecast of the latest 12Z SHIPS intensity model. The HWRF model foresees a Catgeory 2 hurricane with 110 mph winds at landfall in Cuba, while the GFDL calls for a Category 1 hurricane with 75 mph winds. Regardless of its intensity at landfall, Paloma will bring an exceptionally high storm surge of 17-23 feet to the coast of Cuba, since the hurricane has set a large volume of ocean in motion with its Category 4 winds. There is also a large area of shallow water just offshore the south coast of Cuba that will allow the storm surge to pile up to a great height. Cuba will take a terrific pounding from Paloma, and damage from the triple crunchings delivered by Hurricanes Gustav, Ike, and Paloma will make 2008 the worst hurricane season in Cuban history. The latest H*Wind analysis of Integrated Kinetic Energy from NOAA's Hurricane Research Division puts the potential wind damage at 2.6 on a scale of 1 to 6, and the potential storm surge damage at 2.5 on a scale of 1 to 6. The relatively low storm surge potential is misleading, since Paloma is headed toward a portion of the Cuban coast that is highly prone to storm surge.

Passage over Cuba combined with extremely high values of wind shear should tear apart Paloma before it reaches the central and southeastern Bahamas. The HWRF, GFDL, and SHIPS intensity models are all calling for Paloma to dissipate or be a tropical storm or tropical depression by the time it arrives in the Bahamas on Sunday, and this is a reasonable forecast. Paloma has virtually no chance of surviving long enough to threaten Florida.

Links to follow
Radar from Camaguey, Cuba
Santa Cruz del Sur, Cuba weather

A new record for the hurricane season of 2008
This year is now the only hurricane season on record in the Atlantic that has featured major hurricanes in five separate months. The only year to feature major hurricanes in four separate months was 2005, and many years have had major hurricanes in three separate months. This year's record-setting fivesome were Hurricane Bertha in July, Hurricane Gustav in August, Hurricane Ike in September, Hurricane Omar in October, and Hurricane Paloma in November.

Paloma is now the second strongest November hurricane on record in the Atlantic. Hurricane Lenny of 1999, a Category 4 hurricane with 155 mph winds, was the strongest November hurricane on record. Paloma shares second place with Hurricane Michelle of 2001 (Cat 4, 140 mph) and Hurricane Greta of 1956 (Cat 4, 140 mph).

I'll have an update Sunday, possibly not until the afternoon.

Jeff Masters

Paloma near Category 2 strength

By: JeffMasters, 8:02 PM GMT on November 07, 2008

Hurricane Paloma continues to intensify. The latest data from the Hurricane Hunters indicate that the storm is close to Category 2 strength. Between 1 pm and 3 pm EST, an Air Force Hurricane Hunter aircraft dropped two sondes in the northwest eyewall of Paloma, and found winds of 90 and 97 mph at the surface from these sondes. The threshold of Category 2 strength is 96 mph. Winds at the surface measured by the SFMR instrument were as high as 92 mph, and the NOAA aircraft just records 101 mph winds at 3:15 pm EST. Sondes released by a NOAA Hurricane Hunter aircraft in the past hour have found winds of 90 mph in the southeast eyewall, 69 mph in the southwest eyewall, and 67 mph in the northwest eyewall. Clearly, the right (east) side of Paloma is the stronger side, since the forward speed of the hurricane adds to the rotational speed of the vortex on the right side of a Northern Hemisphere hurricane. The central pressure of Paloma is dropping at about 3 mb per hour. The Hurricane Hunters noted that Paloma appeared to be forming a second eyewall concentric with the main eyewall at 1:30 pm, and there was also evidence of this on visible satellite loops. There was also a gap noted in the SSW side of the eyewall by the Hurricane Hunters at 1:30 pm, but this gap was gone by 3 pm. The storm is undergoing some substantial structural changes, and is probably entering a rapid deepening phase. Formation of a secondary concentric eyewall will ordinarily slow down intensification of a hurricane, but is also spreads out the highest winds over a larger area. I'm not convinced that a concentric eyewall is forming, though. Recent infrared imagery shows that the eye has warmed, indicating strengthening. Some very impressive thunderstorms with high, cold tops are firing up at several points in the eyewall (Figure 1), also indicative of strengthening. These thunderstorms may be "hot towers", which are often observed when a hurricane is embarking upon a major intensification phase.

Winds at the Grand Cayman airport were 38 mph, gusting to 53 mph at 2 pm EST, and heavy rain was falling. The airport has received 2.44" of rain so far today. According to wunderground member Jennie Henning at 2 pm today: Conditions here on the island are getting worse - the wind is roaring an the rain is horizontal at times. We're busy locking up and bunkering down.


Figure 1. Visible satellite image of Paloma showing very intense thunderstorms developing at several points along the eyewall.

The intensity forecast
Wind shear is a moderate 10-15 knots, and is expected to slowly increase to 20 knots Saturday morning and above 35 knots on Saturday night. Paloma should be able to intensify until it reaches a point near 20° North Latitude (between the Cayman Islands and Cuba) Saturday morning. I expect Paloma will be at Category 2 strength with 105-110 mph winds when it passes near or over Grand Cayman Island tonight, and will briefly intensify to Category 3 strength after passing Grand Cayman. By Saturday morning, shear should rapidly weaken Paloma, and the hurricane will probably make landfall on Cuba Saturday afternoon or evening as a strong Category 1 hurricane. Passage over Cuba and continued high wind shear will further weaken Paloma before it arrives in the Bahamas Sunday night, and I expect Paloma will be a tropical storm with 45-55 mph winds as it blows through the Bahamas. The latest (12Z, 7 am EST) run of both the HWRF and GFDL models predict that Paloma will hit Grand Cayman Island between 9 pm and 1 am EST tonight. The GFDL predicts Paloma will be a Category 2 storm with 100-105 mph winds, while the HWRF predicts only 85 mph winds. The latest 18Z SHIPS model puts Paloma as a Category 2 hurricane with 105 mph winds at landfall in Grand Cayman. The GFDL and HWRF predict a landfall in Cuba Saturday afternoon as a Category 2 hurricane with 100-105 mph winds.

The track forecast
A strong trough of low pressure approaching the U.S. East Coast is pulling Paloma to the north, and this trough should continue to pull the storm northwards and then turn it northeastward by Saturday morning. It appears likely that Grand Cayman will receive hurricane force winds from Paloma, and there is a 70% chance the island will get hit with a portion of the eyewall. The HWRF model is predicting that Little Cayman and Cayman Brac should only see top sustained winds of 50 mph, but the GFDL predicts a little eastward jog that would bring Category 2 winds of 100 mph to these islands. It will be a close call. Jamaica should see winds of just 20-30 mph from Paloma.

Damage potential for Paloma
Grand Cayman Island is not that prone to large storm surges, since it lies in deep water, and a hurricane's surge tends to flow around the island rather than get pushed up onto shore. The main concern from Paloma is wind damage. A direct hit from a Category 2 hurricane would likely do about $100 million dollars in damage, a nasty blow for an island that just this year finished recovering from the devastating punch delivered by Hurricane Ivan of 2004. Ivan damaged or destroyed 85% of the islands buildings, and caused $1.85 billion in damage. Much of Grand Cayman still remained without power, water, or sewer services for several months after the hurricane. The latest H*Wind analysis of Integrated Kinetic Energy from NOAA's Hurricane Research Division puts the potential wind damage at 1.2 on a scale of 1 to 6, and the potential storm surge damage at 1.5 on a scale of 1 to 6. These numbers will increase later today, but Paloma should be nothing like Hurricane Ivan.

According to the insurance company AIR Worldwide: Insured residential properties are dominated by wood frame and confined masonry. Commercial properties tend to not exceed six stories and are constructed of reinforced concrete. However, after the destruction wrought by Hurricane Ivan in 2004, the Cayman Islands underwent a major rebuilding process. New construction is now superior to much of the rest of the Caribbean countries in terms of wind resistivity. As a result, depending on Paloma's track through the islands, properties may sustain only minor to moderate damage to roof shingles and non-structural elements.

Links to follow
Grand Cayman airport weather
Grand Cayman weather
Wundermap for the Cayman Islands

Historical November tropical cyclones
(This section is a repeat from this morning's blog entry). Historically, only about 5% of all Atlantic tropical storm activity occurs after November 1. Between 1871 and 2007, 60 tropical storms formed in November. Of these, 29 became hurricanes, and four of these, major hurricanes. There have also been two major hurricanes that formed in October and continued on into November. On average, one tropical storm forms in November every other year, and we can expect a November hurricane about one year in five.

The six major November hurricanes were Hurricane Michelle of 2001 (Cat 4, 140 mph); Hurricane Lenny of 1999 (Cat 4, 150 mph); Hurricane Kate of 1985 (Cat 3, 120 mph); Hurricane Greta of 1956 (Cat 4, 140 mph); Hurricane 10 of 1932 (Cat 4, 135 mph); and Hurricane 7 of 1912 (Cat 3, 115 mph). There have been no major hurricanes in the months December through April.

Major hurricanes in the Atlantic by month, 1851-2008
----------------------------------------------------------------------
May 1
June 3
July 9
August 80
September 149
October 60
November 6

In the list above, if a hurricane was at major hurricane strength in two separate months, it is counted as a major hurricane for both months.

November hurricanes of note
The most extraordinary November hurricane was "Wrong-Way Lenny", which hit the northern Leeward Islands as a strong Category 4 hurricane with 155 mph winds 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.

A new record for the hurricane season of 2008?
This year and 2005 are the only seasons that we've had major hurricanes in the Atlantic in four separate months--July, August, September, and October. If Paloma becomes a major hurricane, it will make 2008 the first year since record keeping began in 1851 to feature major hurricanes in five separate months.

I'll have an update Saturday morning, and possibly later tonight.

Jeff Masters

Hurricane Paloma slowly strengthing as it approaches Grand Cayman

By: JeffMasters, 3:00 PM GMT on November 07, 2008

Hurricane Paloma is slowly strengthening. Satellite estimates of Paloma's strength suggest top winds have increased to 85 mph, making it a strong Category 1 hurricane. Visible satellite images show that Paloma continues to be well organized, and it appears an eye is ready to pop out. We haven't had a Hurricane Hunter aircraft in the eye since 3:39 am EST when a NOAA Hurricane Hunter aircraft measured a 982 mb pressure and 80 mph winds, so we don't know the strength of Paloma very well. The Hurricane Hunters noticed that the eyewall had a gap in its west side (Figure 1). This lack of a complete eyewall has slowed down Paloma's intensification, and is probably due to the 10-15 knots of wind shear currently impacting the storm.

Winds at the Grand Cayman airport were 33 mph, gusting to 47 mph at 10 am EST this morning, and heavy rain was falling. Over the past four days, about 4-5 inches of rain has fallen on Grand Cayman, with about 1.5" falling between midnight and 8 am today.

From wunderground member XL this morning:
I live about 100 yards from the sea on the northwest point of Grand Cayman. It is getting quite rough here now. It's been raining non stop for hours and is pretty windy. The sea is also getting quite rough with big swells. Hubby has just driven into work and says flooding of roadways is evident already.


Figure 1. Microwave image of Paloma at 1:57 am EST Friday November 7, 2008.The eyewall has a gap on the northwest side.

The intensity forecast
Wind shear has increased to a moderate 10-15 knots, and is expected to slowly increase to 20 knots Friday night and above 30 knots on Saturday morning. Recent infrared imagery shows that the cloud tops have not cooled in recent hours, so no rapid intensification is likely in the short term. Paloma should be able to intensify until it reaches a point near 20° North Latitude (between the Cayman Islands and Cuba) Saturday morning. I expect Paloma will be at Category 2 strength with 100 mph winds when it passes near or over Grand Cayman Island tonight, and will briefly intensify to Category 3 strength after passing Grand Cayman. This intensification will be slower if Paloma is unable to form a complete eyewall today. By Saturday morning, shear should rapidly weaken Paloma, and the hurricane will probably make landfall on Cuba Saturday afternoon or evening as a strong Category 1 hurricane. Passage over Cuba and continued high wind shear will further weaken Paloma before it arrives in the Bahamas Sunday night, and I expect Paloma will be a tropical storm with 45-55 mph winds as it blows through the Bahamas. The latest (06Z, 2am EST) run of both the HWRF and GFDL models predict that Paloma will hit Grand Cayman Island at about 9 pm EST tonight as a Category 1 hurricane with 85 mph winds. The latest 12Z SHIPS model puts Paloma as a strong Category 1 hurricane with 95 mph winds at landfall in Grand Cayman.

The track forecast
A strong trough of low pressure approaching the U.S. East Coast is pulling Paloma to the north, and this trough should continue to pull the storm northwards and then turn it northeastward by Saturday morning. Several major models continue to predict that Paloma will be torn in two by the wind shear just south of Cuba, with the low level remnants getting forced westward towards the Yucatan Peninsula. This solution seems unlikely, given Paloma's current excellent organization and increasing intensity. I expect Paloma will follow the track of the GFDL, HWRF, and GFS models, which show the storm crossing Cuba and passing through the central Bahamas. It appears likely that Grand Cayman will receive hurricane force winds from Paloma, and there is a 50% chance the island will get a portion of the eyewall hitting it. Little Cayman and Cayman Brac should only see top sustained winds of 50 mph, and the west end of Jamaica should see winds of just 20-30 mph from Paloma.

Damage potential for Paloma
Grand Cayman Island is not that prone to large storm surges, since it lies in deep water, and a hurricane's surge tends to flow around the island rather than get pushed up onto shore. The main concern from Paloma is wind damage. A direct hit from a Category 2 hurricane would likely do about $100 million dollars in damage, a nasty blow for an island that just this year finished recovering from the devastating punch delivered by Hurricane Ivan of 2004. Ivan damaged or destroyed 85% of the islands buildings, and caused $1.85 billion in damage. Much of Grand Cayman still remained without power, water, or sewer services for several months after the hurricane. The latest H*Wind analysis of Integrated Kinetic Energy from NOAA's Hurricane Research Division puts the potential wind damage at 1.1 on a scale of 1 to 6, and the potential storm surge damage at 1.4 on a scale of 1 to 6. These numbers will increase later today, but Paloma should be nothing like Hurricane Ivan.

Links to follow
Grand Cayman airport weather
Grand Cayman weather
Wundermap for the Cayman Islands

Historical November tropical cyclones
Historically, only about 5% of all Atlantic tropical storm activity occurs after November 1. Between 1871 and 2007, 60 tropical storms formed in November. Of these, 29 became hurricanes, and four of these, major hurricanes. There have also been two major hurricanes that formed in October and continued on into November. On average, one tropical storm forms in November every other year, and we can expect a November hurricane about one year in five.

The six major November hurricanes were Hurricane Michelle of 2001 (Cat 4, 140 mph); Hurricane Lenny of 1999 (Cat 4, 150 mph); Hurricane Kate of 1985 (Cat 3, 120 mph); Hurricane Greta of 1956 (Cat 4, 140 mph); Hurricane 10 of 1932 (Cat 4, 135 mph); and Hurricane 7 of 1912 (Cat 3, 115 mph). There have been no major hurricanes in the months December through April.

Major hurricanes in the Atlantic by month, 1851-2008
----------------------------------------------------------------------
May 1
June 3
July 9
August 80
September 149
October 60
November 6

In the list above, if a hurricane was at major hurricane strength in two separate months, it is counted as a major hurricane for both months.

November hurricanes of note
The most extraordinary November hurricane was "Wrong-Way Lenny", which hit the northern Leeward Islands as a strong Category 4 hurricane with 155 mph winds 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.

A new record for the hurricane season of 2008?
This year and 2005 are the only seasons that we've had major hurricanes in the Atlantic in four separate months--July, August, September, and October. If Paloma becomes a major hurricane, it will make 2008 the first year since record keeping began in 1851 to feature major hurricanes in five separate months.

I'll have an update this afternoon.

Jeff Masters

Paloma nears hurricane strength

By: JeffMasters, 8:01 PM GMT on November 06, 2008

Tropical Storm Paloma continues to steadily strengthen, and is well on its way to becoming a hurricane. The latest 2:20 pm EST center fix from the Hurricane Hunters found that the pressure had fallen to 994 mb, and the surface winds had increased to 60 mph. The crew reported that Paloma has built a 20-mile diameter eyewall that is 3/4 complete, with only a gap on the southwest side. Bouy 42057 reported sustained winds of 60 mph, gusting to 74 mph, at 6:50 pm EST. Visible satellite images show that Paloma continues to grow more organized, with low level spiral bands wrapping around the center and upper level outflow expanding on all sides.


Figure 1. Microwave image of Paloma at 7:15 am EST Thursday November 6, 2008. A partial eyewall is evident on the southeast side of the center. Image credit: Navy Research Lab, Monterey.

The intensity forecast
Wind shear remains a very low 0-5 knots, and is expected to remain very low through Friday night. Wind shear will increase to 10-15 knots Friday night and Saturday, as the storm heads north, but I don't expect Paloma will stop intensifying until it crosses 20° North Latitude (between the Cayman Islands and Cuba) Saturday night, when the shear will increase to 30-50 knots. Water temperatures are warm, 29°C, and this warm water extends to great depth. These are very favorable conditions for intensification, and Paloma should be a hurricane by tonight or Friday morning. The latest (12Z, 7am EST) run of the HWRF model predicts Paloma will pass though the Cayman Islands on Saturday morning as a Category 2 hurricane. The GFDL model predicts a Category 3 hurricane, and the latest 18Z SHIPS model puts Paloma as a strong Category 1 hurricane with 95 mph winds in the Caymans. I believe Paloma will be a Category 3 hurricane by Saturday when it passes through the the Cayman Islands. Paloma will likely be a Category 1 or 2 hurricane at landfall in Cuba, and a strong tropical storm with 60-70 mph winds in the Bahamas.

The track forecast
A strong trough of low pressure approaching the U.S. East Coast is pulling Paloma to the north, and this trough should continue to pull the storm northwards and then turn it northeastward by Saturday. Several major models--the NOGAPS, UKMET, and ECMWF--continue to predict that Paloma will be torn in two by the wind shear just south of Cuba, with the low level remnants getting forced westward towards the Yucatan Peninsula. This solution seems unlikely, given the fact that Paloma is likely to grow much stronger and more resistant to wind shear than these models are predicting. I expect Paloma will follow the track of the GFDL, HWRF, and GFS models, which show the storm may pass very close to Grand Cayman Island on Saturday, then make landfall in southern Cuba on Sunday and continue on through the central Bahamas. On this track, Grand Cayman may receive a direct hit, but Little Cayman and Cayman Brac would only see top sustained winds of 50 mph. A slight deviation to the right, though, would put Little Cayman and Cayman Brac in the bulls-eye. Jamaica should see winds of just 20-30 mph from Paloma.

Links to follow
Buoy 42057
Grand Cayman airport weather
Grand Cayman weather
Wundermap for the Cayman Islands
Wundermap for 18N 83W

Historical note
This year and 2005 are the only seasons that we've had major hurricanes in the Atlantic in four separate months--July, August, September, and October. If Paloma becomes a major hurricane, it will make 2008 the first year since record keeping began in 1851 to feature major hurricanes in five separate months.

I'll have an update Friday morning.

Jeff Masters

Paloma forms and steadily intensifies

By: JeffMasters, 3:17 PM GMT on November 06, 2008

Tropical Storm Paloma formed last night, and is steadily strengthening. Visible satellite images show a significant increase in organization of the storm is occurring, with low level spiral bands beginning to wrap around the center and upper level outflow expanding on all sides except to the south. Recent microwave images (Figure 1) indicate that Paloma is already starting to build an eyewall.


Figure 1. Microwave image of Paloma at 7:15 am EST Thursday November 6, 2008. A partial eyewall is evident on the southeast side of the center. Image credit: Navy Research Lab, Monterey.

The intensity forecast
Wind shear has dropped to a very low 0-5 knots, and is expected to remain very low, 0-5 knots, over the next day. Wind shear will increase to 10-15 knots Friday and Saturday, as the storm heads north, but I don't expect Paloma will stop intensifying until it crosses 20° North Latitude (between the Cayman Islands and Cuba) Saturday night, when the shear will increase to 30-50 knots. Water temperatures are warm, 29°C, and this warm water extends to great depth. These are very favorable conditions for intensification, and Paloma should be a hurricane by Friday. I expect Paloma will be a Category 2 or 3 hurricane when it passes through the Cayman Islands on Saturday. The latest (6Z, 1am EST) of the HWRF model predicts Paloma will pass though the Cayman Islands on Saturday morning as a Category 3 hurricane. The GFDL and SHIPS intensity models are less aggressive, predicting a Category 1 hurricane. I believe a Category 3 hurricane is more likely than a Category 1 hurricane for the Cayman Islands, and Paloma has the potential to imitate Hurricane Michelle of 2001. Michelle formed in the same region at the same time of year, and took just three days to intensify from a tropical depression to a Category 4 hurricane. Michelle made landfall in central Cuba as a Category 4 hurricane, then weakened to a Category 1 hurricane as it passed through the Bahamas. Paloma will likely be a Category 1 or 2 hurricane at landfall in Cuba, and a strong tropical storm with 60-70 mph winds in the Bahamas.

The track forecast
A strong trough of low pressure approaching the U.S. East Coast is pulling Paloma to the north, and this trough should continue to pull the storm northwards and then turn it northeastward by Saturday. Several major models--the NOGAPS, GFS, and ECMWF--predict that Paloma will be torn in two by the wind shear just south of Cuba, with the low level remnants getting forced westward towards the Yucatan Peninsula. This solution seems unlikely, given the fact that Paloma is likely to grow much stronger and more resistant to wind shear than these models are predicting. I expect Paloma will follow the track of the GFDL, HWRF, and GFS models, which show the storm may pass very close to Grand Cayman Island on Saturday, then make landfall in southern Cuba on Sunday and continue on through the central Bahamas.

Links to follow
Wundermap for 16N 83W

I'll have an update this afternoon. A new Hurricane Hunter plane is on its way to Paloma, and should arrive at the center around 1 pm EST.

Jeff Masters

Tropical Depression 17 forms

By: JeffMasters, 8:33 PM GMT on November 05, 2008

An Air Force Hurricane Hunter plane has arrived in the area of disturbed weather 150 miles southeast of the northeastern tip of Nicaragua and found Tropical Depression 17 has formed. The aircraft found a broad center of low pressure with top winds at flight level (600-1000 feet) of 30 mph. The central pressure was 1004 mb, and the plane did see two squalls of 54-58 mph winds at the surface with their SFMR instrument. Visible satellite images have shown a significant increase in the intensity and areal coverage of the heavy thunderstorm activity this afternoon. An upper-level outflow channel has opened to the north, and the latest microwave image from the TRMM satellite shows that low-level spiral bands are beginning to form, though the center of the storm remains broad.


Figure 1. Current satellite image of TD 17.

The intensity forecast
Wind shear has dropped to a low 5 knots this afternoon, and is expected to remain very low, 0-5 knots, over the next two days. Water temperatures are warm, 29°C, and this warm water extends to great depth. These are very favorable conditions for intensification--if the storm avoids passing too close to land near the northeast coast of Nicaragua. The latest (12Z, 7am EST) runs of both the GFDL and HWRF models predict 93L will not interact will land enough to weaken the storm, and predict TD 17 will pass though the Cayman Islands on Saturday morning as a Category 2 hurricane, and strengthen to a Category 3 or 4 hurricane by landfall Sunday morning in central Cuba. The SHIPS intensity model is less aggressive, predicting a strong tropical storm with 70 mph winds by Saturday. I give TD 17 a 70% chance of becoming a hurricane, and a 40% chance of becoming a major hurricane. The storm has the potential to imitate Hurricane Michelle of 2001. Michelle formed in the same region at the same time of year, and took just three days to intensify from a tropical depression to a Category 4 hurricane. Michelle made landfall in central Cuba as a Category 4 hurricane, then weakened to a Category 1 hurricane as it passed through the Bahamas.

The track forecast
A slow north-northwest motion to a point just offshore the Nicaragua-Honduras border is likely for TD 17 through Thursday. At that time, a strong trough of low pressure will be approaching the U.S. East Coast. There is some uncertainty whether this trough will be strong enough to lift TD 17 northwards across Cuba. Two major models, the NOGAPS and GFS, predict that TD 17 will be too weak to "feel" the influence of this trough, and they keep the storm trapped in the Caribbean near Honduras and Nicaragua. If this solution is correct, a major rain event for northern Nicaragua and Honduras is possible, with heavy rains of 5-10 inches likely to cause life-threatening flash floods and mudslides. The storm would likely intensify to a tropical storm or Category 1 hurricane, depending upon how much interaction with land occurs. On the other hand, the GFDL, HWRF, and ECMWF models predict that TD 17 will be strong enough to feel the trough. These models predict a northward motion through the Cayman Islands on Saturday, followed by a northeast turn and a landfall in central or eastern Cuba on Sunday morning. On Sunday afternoon, TD 17 would then pass through the central Bahamas as it accelerates to the northeast. These models predict a deeper, stronger storm that is more likely to feel the influence of the trough. The UKMET model is between these two solutions, and predicts TD 17 will get stranded in the Western Caribbean near the western tip of Cuba.

Given the current increasing trend in organization, I believe TD 17 will grow deep enough and strong enough to get pulled northward by the trough. The storm should move through the Cayman Islands on Saturday and across central or eastern Cuba on Sunday, as the GFDL, HWRF, and ECMWF models are predicting. There is the potential that the storm could enter a period of rapid intensification on Saturday, bringing it to major hurricane status. Residents of the Cayman Islands, western Jamaica, and central and western Cuba should anticipate the possibility of a hurricane--possibly a major hurricane--affecting them Saturday and Sunday. If TD 17 crosses Cuba as expected and moves into the Bahamas, it will weaken due to the interaction with land and the presence of very high wind shear of 30-50 knots just north of Cuba. These effects should weaken the storm by at least 40 mph before it passes through the Bahamas. The HWRF and GFDL models predict TD 17 could be a Category 2 hurricane in the Bahamas, but I think a Category 1 hurricane is more likely.

Links to follow
Wundermap for 16N 83W

I'll have an update Thursday morning.

Jeff Masters

Caribbean disturbance 93L continues to grow more organized

By: JeffMasters, 2:42 PM GMT on November 05, 2008

An area of disturbed weather (93L), a few hundred miles east of the coast of Nicaragua, continues to slowly organize. This morning's QuikSCAT pass revealed that the circulation center is broad and ill-defined, and the satellite noted winds of about 30 mph in the heaviest thunderstorms. Visible satellite images show that heavy thunderstorm activity has shown a moderate increase in intensity and areal coverage this morning. An upper-level outflow channel has opened to the north, but there is no evidence of low-level spiral bands forming yet.


Figure 1. Current satellite image of 93L.

The forecast
Wind shear has dropped to a low 5-10 knots this morning, and is expected to remain in the low to moderate range, 5-15 knots, over the next three days. The phase of the Madden-Julian Oscillation has changed to positive over the Western Caribbean over the past few days, and this should act to reduce wind shear and enhance the storm's updrafts and instability. Nearly all of the tropical cyclones that have formed in the Atlantic this season have formed under a positive Madden-Julian phase. Water temperatures are warm, 29.5°C, and this warm water extends to great depth. These are favorable conditions for intensification, and both the GFDL and HWRF models predict 93L will become a hurricane, with the HWRF predicting a major hurricane. The SHIPS intensity model is less aggressive, predicting a strong tropical storm with 65 mph winds by Saturday. I give 93L a 50% chance of eventually becoming a hurricane, and a 20% chance of becoming a major hurricane. These odds will increase tomorrow if 93L can avoid passing close enough to the northeast coast of Nicaragua for significant weakening due to land interaction. This storm has the potential to imitate Hurricane Michelle of 2001. Michelle formed in the same region at the same time of year, and took just three days to intensify from a tropical depression to a Category 4 hurricane. Michelle made landfall in central Cuba as a Category 4 hurricane, then weakened to a Category 1 hurricane as it passed through the Bahamas.

A slow north-northwest motion to a point just offshore the Nicaragua-Honduras border is likely for 93L through Thursday. At that time, a strong trough of low pressure will be approaching the U.S. East Coast. Only one major model, the NOGAPS, predicts that this trough will be too weak to turn 93L northwards, and I am discounting this solution at present. The other five major models agree on a northward motion, bringing 93L near the Cayman Islands or western Jamaica on Saturday, followed by a northeast turn. On Sunday morning, 93L should make landfall in Western Cuba, then pass through the central or eastern Bahamas on Sunday afternoon as it accelerates to the northeast.

Given the current increasing trend in organization, I believe 93L will become a tropical depression tonight or Thursday morning. NHC is giving 93L a high (>50% chance) of developing into a tropical depression by Friday morning. There is the potential that 93L could enter a period of rapid intensification on Saturday, bringing it to hurricane status. Residents of the Cayman Islands, Jamaica, and western Cuba should anticipate the possibility of a hurricane affecting them Saturday and Sunday. If 93L crosses Cuba as expected and moves into the Bahamas, it will weaken due to the interaction with land and the presence of very high wind shear of 30-50 knots just north of Cuba. These effects should weaken the storm by at least 40 mph before it passes through the Bahamas. The HWRF model predicts 93L could be a Category 2 hurricane in the Bahamas, but I think a tropical storm is more likely.

Northeastern Nicaragua and northeastern Honduras are at risk of heavy rains from 93L today through Friday morning. Total rainfall amounts of 4-8 inches are likely. Rains of 1-2 inches fell last night in Jamaica, and heavy rains of 4-8 inches should affect Jamaica and the Cayman Islands Thursday through Saturday. The first Hurricane Hunter flight into 93L is scheduled for this afternoon.

Links to follow
Wundermap for 16N 83W

I'll have an update this afternoon when the new model runs are in and the Hurricane Hunter data is available.

Jeff Masters

Caribbean disturbance 93L growing more organized

By: JeffMasters, 3:59 PM GMT on November 04, 2008

An area of disturbed weather (93L) a few hundred miles east of the Nicaraguan coast, is growing more organized, and has the potential to develop into a tropical storm this week. This morning's QuikSCAT pass revealed that the circulation center near 12N 81W is better defined and is more circular. However, visible satellite images show that the heaviest thunderstorm activity is about 200 miles to the north of the center, and there is very little heavy thunderstorm activity near the center. It appears that the center of circulation is now attempting to relocate near the heaviest thunderstorms, somewhere near 14N 81W. This relocation will make last night's model runs a poor judge of how 93L might develop. The disturbance has been drifting west-northwest to northwest over the past 18 hours. Wind shear is a moderate 15 knots, and heavy thunderstorm activity has shown a moderate increase in intensity and areal coverage over the past few hours.


Figure 1. Current satellite image of 93L.

The forecast
Wind shear is expected to remain in the moderate range, 10-20 knots, over the southern Caribbean during the next three days. Water temperatures are warm, 29.5°C, and this warm water extends to great depth. These are favorable conditions for intensification, and both the GFDL and HWRF models predict 93L will become a hurricane, with the HWRF predicting a major hurricane. However, the SHIPS intensity model predicts only a weak tropical storm with 40 mph winds. I give 93L a 40% chance of eventually becoming a hurricane.

Steering currents are weak, but a slow northwest motion to a point just offshore the Nicaragua-Honduras border is likely through Thursday. At that time, a strong trough of low pressure will be approaching the U.S. East Coast. The models are split on whether this trough will be strong enough to pull 93L northward. The GFDL, HWRF, and ECMWF models predict the trough will turn 93L northward then northeastward, bringing the storm near the Cayman Islands by Saturday and Jamaica by Sunday. The UKMET, GFS, and NOGAPS models disagree, bringing 93L ashore over northern Nicaragua by Friday, and keeping the storm trapped near the north coast of Honduras through Monday. Given the probable center re-formation 200 miles to the north currently underway, the more northerly threat to the Cayman Islands and Jamaica appears to be the more likely scenario.

Given the current increasing trend in organization, I believe 93L will become a tropical depression on Wednesday and Tropical Storm Paloma by Thursday. NHC is giving 93L a medium (20%-50% chance) of developing into a tropical depression by Thursday morning.

Northeastern Nicaragua and northeastern Honduras are at risk of heavy rains from 93L beginning Wednesday. Total rainfall amounts of 4-8 inches are likely through Thursday in the region. These heavy rains may spread westward to the Belize border by Friday, if the storm resists being pulled northward by the trough. Panama and Costa Rica should receive only another 1-2 inches. Heavy rains will likely move into the Cayman Islands and Jamaica on Wednesday or Thursday, and may affect Cuba by Friday and Haiti by Saturday. Currently, no models are showing a threat to Florida or the Bahamas from 93L, but that could change with the next set of model runs, after the center re-formation is taken into account. The first Hurricane Hunter flight into 93L is scheduled for Wednesday afternoon.

Links to follow
Wundermap for 16N 84W

I'll have an update Wednesday morning, or later today if there's a major change to report. It's time to go vote!

Jeff Masters

Disturbance 93L in southern Caribbean may develop later this week

By: JeffMasters, 2:54 PM GMT on November 03, 2008

An area of disturbed weather (93L), associated with a broad area of low pressure that formed at the tail end of a stalled-out cold front, continues in the south-central Caribbean Sea. The disturbance has a strong potential to develop into a tropical storm by late this week. This morning's QuikSCAT pass missed 93L, but last night's QuikSCAT pass revealed an elongated circulation center near 11N 79W, about 300 miles north of the Panama Canal. Wind shear is a low to moderate 5-15 knots over the disturbance. Visible satellite images show that heavy thunderstorm activity has changed little in coverage or intensity over the past day in association with 93L, and the storm is quite disorganized at present. However, precipitable water imagery shows that the atmosphere has moistened considerably over the south-central Caribbean over the past day, and I expect a marked increase in heavy thunderstorm activity over the region by Tuesday.


Figure 1. Current satellite image of 93L.

The forecast
Wind shear is expected to remain in the moderate range, 10-20 knots, over the southern Caribbean during the remainder of the week. Water temperatures are warm, 29.5°C, and this warm water extends to great depth. These are favorable conditions for intensification, and both the GFDL and HWRF models predict 93L will become a hurricane. However, the SHIPS intensity model does not develop 93L at all.

Steering currents are weak, but a slow west-northwest to northwest motion of 93L is likely beginning on Tuesday, when an intensifying extratropical storm off the east coast of Florida should impart northwesterly steering currents over the southern Caribbean. Most of the models foresee that 93L will move to a point just offshore the Nicaragua-Honduras border by Thursday. At that time, a strong trough of low pressure will be approaching the U.S. East Coast. Most of the models predict that this trough will be strong enough to pull 93L northward towards western Cuba (GFDL and UKMET models), or even northeastwards, towards eastern Cuba and Jamaica (HWRF and ECMWF models). These two models foresee a possible threat to the Bahamas or South Florida late this week or early next week. The GFS model predicts the trough will not be strong enough to turn 93L northwards, and predicts a landfall in Nicaragua late this week. Since this is the outlier, I am discounting this solution, and predict that 93L will remain over water this week, becoming Tropical Storm Paloma Wednesday or Thursday. NHC is giving 93L a medium (20%-50% chance) of developing into a tropical storm by Wednesday morning. I give 93L a 40% chance of eventually becoming a hurricane.

Northeastern Nicaragua and northeastern Honduras are at risk of heavy rains from 93L beginning Tuesday. Total rainfall amounts of 4-8 inches are likely through Wednesday in these countries. Panama and Costa Rica will probably receive about 2-4 inches of rain through Wednesday. Heavy rains will likely move into the Cayman Islands on Wednesday.

I'll have an update Tuesday morning.

Jeff Masters

Disturbance near Panama a threat to develop

By: JeffMasters, 5:18 PM GMT on November 02, 2008

An area of disturbed weather, associated with the tail end of a stalled-out cold front, has developed in the south-central Caribbean Sea. This disturbance has a strong potential to develop into a tropical storm by late this week. This morning's QuikSCAT pass revealed an elongated circulation center near 11N 77W, about 300 miles northeast of the Panama Canal. Wind shear is a moderate 10-20 knots over the disturbance, and visible satellite images show that heavy thunderstorm activity is increasing in coverage and intensity across most of the south-central Caribbean.


Figure 1. Current visible satellite image of the Caribbean. Image credit: NOAA.

The forecast
Wind shear is expected to remain in the moderate range, 10-20 knots, over the southern Caribbean during the remainder of the week. Most of the models support additional development of this disturbance, though none of them show anything stronger than a weak tropical storm developing this week. Steering currents are weak, but a slow west-northwest to northwest motion is likely beginning on Tuesday, when an intensifying extratropical storm off the east coast of Florida should impart northwesterly steering currents over the southern Caribbean. I give a high (>50% chance) that this disturbance will develop into Tropical Storm Paloma this week, and a 40% chance that it will eventually become a hurricane. Northeastern Nicaragua and Honduras appear most at risk of heavy rains from the disturbance, although Panama and Costa Rica may also begin receiving heavy rains on Monday. The ECMWF model predicts that the disturbance will move over Jamaica on Friday, and it certainly possible that the Cayman Islands, Jamaica, eastern Cuba, and Haiti may receive heavy rains from this storm by the end of the week. It is unlikely that the disturbance will affect the U.S. this week.

I'll have an update Monday morning.

Jeff Masters


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

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About

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