Weatherdem's Weblog

Bridging climate science, citizens, and policy

Atlantic Tropical Weather Update 8/17/09 #3

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Things in the Atlantic are temporarily winding down as fast as they were wound up.  Tropical Storm Claudette made landfall over the panhandle of Florida this morning.  Tropical Depression Ana has totally decayed and is just a broad area of lower surface pressures and scattered thunderstorms over the Atlantic.

Hurricane Bill remains the only game in town for the moment.  Here are his vitals tonight:

Center located at 15N, 48.3W; moving WNW @ 17mph; maximum sustained winds of 100mph; minimum central pressure of 967mb.

The 100mph/967mb readings mean Bill is a solid Category 2 Hurricane tonight.  His pressure reading decreased throughout the day, so further strengthening is likely tomorrow – Bill should become the first major hurricane of the 2009 season.

Bill looks outstanding on satellite imagery – a classic-looking hurricane with strong outflow to all quadrants, spiral bands and a developing eye-wall visible from space.

The official track forecast calls for Bill to turn further to the NW tomorow around the subtropical ridge over the Atlantic.  That northwesterly motion should continue for a couple of days before further turning steers the storm even more northerly at the end of the week.  All the models show this behavior for Bill.  Some are a little more aggressive with the NW to N turning by the end of the 5-day forecast period.  The rate of turning will likely only make a difference with whether Bill eventually hits eastern Canada or become extra-tropical and eventually makes his way to Europe.

The official intensity forecast calls for Bill to become a Category 3 storm by tomorrow night.  Bill is riding over 27.5C waters, which will only get warmer the further west he travels.  There are no regions of damaging shear forecasted to affect the storm within the next few days, so the environment is ripe for Bill to strengthen.  I think there is a decent chance that Bill might be a Category 3 between 12p and 6P local time (Bill’s) tomorrow.

The tropical wave that exited Africa after Bill has no chance of development.  There is a wave behind the first that is just now starting to move over the Atlantic.  This wave isn’t as vigorous as the one that spawned Bill, but more impressive than the wave that generated Ana.  It’s riding close to 10N, which would give it extra time as it crosses the Atlantic to develop.  Relativey low SSTs, and cooler waters stirred to the surface by Bill will act as inhibitors of tropical development.  In fact, we might have to wait for a couple of waves to come off before conditions are really favorable again.


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