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