Wednesday, August 22, 2012

Tropical Storm Isaac and Tropical Depression 10: August 22, Update B

I just drove back from Tallahassee with almost nary a raindrop despite the clouds, unlike the Lesser Antilles. I sure hope no-one went to the Caribbean for a holiday in the sun this week!

Tropical Storm Isaac
The NHC ‘relocated’ his center southward and it is now officially at 15.8N, 63.0W, heading W at 20 mph. Consequently the track has been shifted farther south so it won’t pass quite as close to Puerto Rico as they previously thought. I still think the official forecast track is a little too far north.At the moment I continue to think that his path will be more westward/southern compared to the official track until early Friday, keeping him around the 15-16 N latitude.

After that it is still a tricky call. You can see the low pressure front that is causing all the ruckus in this satellite image of the Atlantic:

It is still over Florida… it’s been there for two days now! The dilemma is whether or not that front will have moved southeastward enough to meet him when he is in the area of Hispaniola/Cuba (in which case he will be whisked across Hispaniola/Cuba and on the Atlantic side of Florida), or will he be south enough to sneak across the Caribbean (westward) and avoid it either entirely (in which case he’s heading to Mexico) or until he is closer to the Gulf (in which case he may be making a visit to the Gulf side of Florida). (I’m beginning to feel like Vizzini from the Princess Bride! “Now, a clever man would put the poison into his own goblet because he would know that only a great fool would reach or what he is given. I am not a great fool, so I can clearly not choose the wine in front of you. But you must have known that I am not a great fool, so I can clearly not choose the wine in front of me.” etc…)

I will be watching his forward speed tomorrow as well as looking for some sign that the front has decided to take a Caribbean vacation!

The storm took a bit of a beating earlier as it crossed the islands, so although the convection is quite impressive and is improving in the Caribbean, his circulation is still a bit messy because he is still interacting with the islands and there is wind shear. The convection has improved because he has moved away from the dry Saharan air and sea surface temperatures are around 28 deg C, with the upper 75-100m of the water warmer than 26 deg C. The center continues to be broad and the circulation (vorticity) in the lower half of the troposphere decreased a bit. Interestingly, the plane found that the winds are actually less than 45mph, but the NHC have decided to keep that for now which is a good move in my opinion. I think he is on track to become a hurricane by Friday morning at the latest (possibly overnight Thurs/Fri). With official winds of 45mph and central pressure of 1003mb, he is a weak Tropical Storm at the moment (range: 39-73mph). BUT … he is a big boy! Attached is the latest satellite image of the Atlantic showing the areas of convection… he stretches across the entire length of the Lesser Antilles! (you can see the wind shear with the clouds streaming off to the east). So all the islands are experiencing something from Isaac. I heard from Tom on St. Thomas at around noon today: “we are finishing up closing shutters today and putting plants in pots under cover...very windy last night and today it is picking up”.

Tropical Depression 10
The-storm-yet-to-be-named-Joyce is officially at 13.8N, 39.5W, heading WNW at 17mph. Winds are 35mph and it has a central pressure of 1007mb. Not much change here really because it is still interacting with dry air and it is also being influenced a little by Isaac. The official track keeps it as a storm in the Atlantic – possibly heading towards Bermuda. I am not convinced that this will be the track yet, but I can’t really identify a good center because she is so poorly formed so I can’t assess this at the moment but I think there’s a good possibility that it will remain on a more westward track than they think. They also forecast it will become a Tropical Storm tomorrow. Despite the little convection it has (as you can see in the satellite image of the Atlantic), it’s circulation has improved in the lower troposphere and it is moving into an area where the upper tropospheric conditions are ‘storm friendly’ too. I suppose it is possible that it will be strong enough to be named tomorrow, but with the poor formation and convection, it’s pretty borderline.

I think I’ll have to watch The Princes Bride again. In my spare time. In December. After this hurricane season.


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DISCLAIMER: These remarks are just what I think/see regarding tropical storms - not the opinion of any organization I represent. If you are making an evacuation decision, please heed your local emergency management and the National Hurricane Center's official forecast and the National Weather Service announcements. This is not an official forecast. If I "run away, run away" (Monty Python), I'll let you know.


Anonymous said...

Please stop sending your spent storms this way (Dorset UK)We have a Bank Holiday this weekend.
Also have you forgotten how to spell cheque!

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