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Claudette hits Florida; Ana approaches Puerto RIco; Bill becomes our first hurricane

By: Dr. Jeff Masters, 2:10 PM GMT on August 17, 2009

Tropical Storm Claudette made landfall at about 1:15 am EDT near the eastern end of Santa Rosa Island, just southeast of Fort Walton Beach in Florida. Claudette's top winds were around 50 mph. A Personal Weather Station in Eastpoint, FL recorded sustained winds of 49 mph, gusting to 66 mph last night. So far, the rain from Claudette has had a tough time penetrating inland (Figure 2). Heavy rains of 3 - 4 inches have been confined to a narrow strip of coast, and Claudette is unlikely to cause any major flooding. Apalachicola received just over 4 inches of rain so far from Claudette. Radar animations out of the Florida Panhandle show that heavy rains continue along the coast in association with a main spiral band of Claudette, and these rains will gradually subside today.

Figure 1. Radar reflectivity image of Tropical Storm Claudette as it approached landfall just southeast of Fort Walton Beach shortly after midnight on 8/17/09.

The tropics featured a rare triple threat the past two days--simultaneous named storms beginning with the letters A, B, and C. The last time this occurred was in the slow-starting 1984 hurricane season, when Tropical Storms Arthur, Bertha, and Cesar were all active on September 1. This year's A, B, and C storms all got their names in just a 33 hour span. This is not a record, since in 1995, three tropical storms--Humberto, Iris, and Jerry--got their names in a 27-hour span (thanks to NOAA's Ryan Sharp for looking up this stat).

Figure 2. Total precipitation estimated by radar for Claudette, as of 3:28pm EDT 8/17/09.

Ana not dead yet
Tropical Depression Ana continues to cling to life, and is now approaching landfall in Puerto Rico. Radar animations from the San Juan, Puerto Rico radar show a surface circulation just southeast of the island, with some low-level spiral banding trying to develop to the south. Recent satellite images also show a rejuvenation of the heavy thunderstorm activity near Ana's center, as the storm regroups from being nearly torn apart yesterday. Ana has already dumped up to 4 inches of rain along the north coast of Puerto Rico, according to radar-estimates.

It is unlikely that Ana will survive past today, however, since the storm will move over both Puerto Rico and the rugged terrain of Hispaniola. The high mountains of these islands should act to disrupt the relatively small and fragile circulation of Ana. None of the computer models foresee that Ana will survive passage over Hispaniola. The Dominican Republic can expect 3 - 6 inches of rain from Ana, and Haiti can expect 1 - 3 inches.

Figure 3. Total precipitation estimated by radar from Ana for Puerto Rico.

Bill becomes the first Atlantic hurricane of 2009
Hurricane Bill continues to gather strength, and is now the first hurricane of the 2009 Atlantic hurricane season. An eye has appeared on visible and infrared satellite imagery, and Bill is displaying an impressive symmetry, with plenty of low-level spiral banding.

Wind shear is low, 5 - 10 knots, and is forecast to be in the low range through Wednesday. With Sea Surface Temperatures only 27°C today, substantial intensification may not occur until Tuesday and Wednesday, when SSTs warm to 28 - 29°C and ocean heat content sharply increases. By Thursday, Bill is expected to leave the favorable upper-level wind environment it currently finds itself in, and moderate shear of 15 - 20 knots may limit further intensification.

Water vapor satellite imagery shows that there is a modest trough of low pressure in the upper atmosphere near 50°W longitude, that Bill is currently approaching. All of the computer models except the UKMET predict that this trough will be strong enough to turn Bill more to the northwest so that the hurricane misses the Lesser Antilles Islands. The UKMET predicts the trough will not affect Bill much, and that the hurricane will pass through or just north of the islands on Thursday. For now, the UKMET solution is being discounted, since the trough at 50W appears substantial enough on satellite imagery to be able to turn Bill more to the northwest.

A much larger trough of low pressure is expected to develop along the U.S. East Coast late this week, turning Bill even more to the northwest. Most of the models predict Bill will pass very close to Bermuda on Saturday as a result. The HWRF model predicts Bermuda will receive a direct hit at Category 4 strength. Until Bill interacts with the small trough at 50°W, it is too early to be confident of the potential threat to Bermuda. By Tuesday, we should have a much better idea of the threat. Likewise, I would like to see the UKMET model come around in line with the other models before dismissing the possible threat to the U.S. East Coast. It currently appears that Bill will miss the U.S. East Coast, but that a strike on the Canadian provinces of Newfoundland or Nova Scotia is possible.

I'll have an update Tuesday morning, or possibly this afternoon.

Jeff Masters


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