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Atlantic Tropical Weather Update 8/16/09 #1

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The drama in the Atlantic basin continues this weekend.  In the past few days, Tropical Depression Two reformed, then strengthened to Tropical Storm Ana.  Two days behind T.S. Ana, a vigorous tropical wave developed into Tropical Depression Three, then strengthened to Tropical Storm Bill.  Then, a tropical wave that had made its way near Florida interacted with an upper-level trough, sustaining deep convection over a couple of days’ time, developed into Tropical Depression Four overnight last night off the west coast of Florida.  The whole thing happened basically in five days time, but most of the action has taken place in ~24 hours!  So instead of appending updates throughout the day as I did yesterday, I’m going to put up separate posts.  This is Update #1 for 8/16/2009.

This morning, I’ll start with Tropical Depression Four since it is closest to U.S. interests.  Here are T.D. Four’s vitals:

Center located at 28.7N, 84.6W (76 miles SSE of Apalachicola, FL; 125 miles SE of Panama City, FL); moving NNW @ 14mph; maximum sustained winds of 35mph; minimum central pressure of 1011mb – that’s pretty high.

T.D. Four’s official track forecast has shifted considerably since I mentioned it last night.  It isn’t going to move across a good portion of the warm Gulf of Mexico, it’s going to move across a short portion of relatively cooler, shallower waters.  As such, it won’t have a lot of time to get organized before making landfall.  It is currently projected to make landfall just west of Panama City, FL tonight by 6PM.

About the only question is will it have enough time to organize/strengthen into a Tropical Storm before landfall.  The official intensity forecast is predicting that that will happen – about 2PM EDT today (~3 hours from now).  For a relatively new storm, it actually has some impressive organization to it.  I think it will be Tropical Storm Claudette by landfall tonight.  Amazing.  Post-landfall, the system will likely decay quickly Monday and Tuesday.  The threats to Florida and Alabama will be flooding and tornadoes.

Onto Tropical Storm Ana.  Here are T.S. Ana’s vitals:

Center located at 14.6N, 54.7W; moving W @ 20mph; maximum sustained winds of 40mph; minimum central pressure of 1005mb.

She’s picked up quite a bit of forward motion in the last day; the central pressure is still pretty high – no indication of rapid intensification in the next few hours.  Her location puts her 436 miles to the east of Martinique, in the middle of the Antilles.

T.S. Ana’s official track forecast has shifted significantly since last night, as I thought it might.  She is expected to shift her movement to the NNW today, pass over the Windward Islands in between Martinique and Guadeloupe, then move into the northeastern Caribbean Sea.  She is forecasted to continue over the south side of Hispanola Tuesday, then over southern Cuba Wednesday and Thursday before emerging over the Gulf of Mexico Thursday night.  In contrast, this time yesterday, the official track forecast put Ana over southern Florida by Thursday.  As such, the track forecast could certainly shift even further in the extended time period.  Most of the model solutions keep Ana on a more southerly route.  Only a couple show her moving to the north of the Caribbean islands in the 5-day forecast period.

T.S. Ana’s official intensity forecast keeps her as a Tropical Storm until moving over Hispanola, after which she should degrade to a Tropical Depression again.  Only one model intensity forecast strengthens Ana in the next few days to a strong Tropical Storm.  She’s simply battling too much dry air and wind shear to strengthen – she’s having a hard enough time maintaining herself.

Now, Tropical Storm Bill.  Here are T.S. Bill’s vitals:

Center located at 11.4N, 37.2W; moving W @ 13mph; maximum sustained winds of 45mph [update]: sustained winds @ 60mph; minimum central pressure of 1002mb.

T.S. Bill is undergoing a process of increasing organization and strengthening.  His official track forecast continues to keep him to the northeast of the Lesser Antilles in the extended forecast (4-5 days out).  I will note that that track forecast is on the southern portion of the model solution set – every model solution moves the storm more to the north in that 4- and 5-day forecast.

Bill’s intensity forecast is the interesting one for weather/hurricane fans.  Bill is forecasted to become a Hurricane by tomorrow and a Major Hurricane by Wednesday morning.  The good news is that intensification will happen far out to sea.  Combined with the favorable track forecast, Bill shouldn’t affect any landmasses with those strong winds.

Bill looks very organized this morning – a very good looking storm on satellite.  There is evidence of strong outflow in all quadrants around the storm – indicative of very healthy airflow.  I definitely think he will strengthen into a hurricane by late tonight – the sun has passed by his position already today, so he has today’s maximum ocean heat content to work with.  He is over 28C waters and will remain over that warm or warmer for a number of days from now.

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