Thursday, August 23, 2012

Tropical Storm Isaac and Tropical Storm Joyce: August 23, Update A

It’s one of those days. “Distressingly little time for sloth or idleness” as Oscar Wilde might write.

Tropical Storm Isaac
The NHC continued to shift his center southwards, which is a relief to me. I don’t need new glasses after all. J And maybe we’ll get a better handle on the forecast track by the end of the day now.

He is currently officially at 15.6N, 65.4W, heading W at 15mph. Winds are officially 40mph, central pressure is 1003mb. Apparently he is barely a Tropical Storm at the moment with winds that low. However, his convection is still impressive, as is his girth. Here is the latest infra-red (convection) satellite image:

No surprise, but I disagree with the NHC. I think his winds are stronger than 40mph. His circulation is very good in the lower half of the troposphere and it looks like it is improving in the upper half of the troposphere as well. There is very little wind shear near his center, although you can see that there is some because the clouds continue to stream off to the east. There is also good ‘outflow’ (ooh, jargon! ;-) ) – this is that wispy/jagged  toothsaw blade sort of pattern in the clouds that you can see in the image. This is another indication that his structure is improving.  

I am also not convinced by the 15.6N, 65.4W center location. I know they have the planes, satellites, radars etc to look at, but I think it is still south of this, and possibly also a little west of this location. Maybe closer to 15N, 66W. The NHC do say that there are multiple areas of circulation (vorticity), and if I squint I can see what they are talking about. But I have seen that in other storms (and this one has had them for the past few days), so I don’t know why they have not been able to follow his center for the past few days. He is reaching the longitude of Puerto Rico, which was my guiding point for his future track. From the pressure fields I’m looking at, it looks like he will continue westward for longer than the forecast track currently shows, which means he won’t be as near to Hispaniola as thought and they probably won’t have hurricane force winds. I think this almost eliminates one of the three scenarios I had yesterday – I don’t think he will make that northward turn in time to cross Hispaniola and onto the Atlantic side of Florida, but more on this later (when I have time). If he’s not going to interact with Hispaniola as forecast, it also changes his intensity forecast by the way.

Tropical Storm Joyce
She’s been named. Currently officially at 15.2N, 42.2W, heading WNW at 17mph. Winds are a weak 40mph, central pressure is 1006mb. The track currently looks like it is going to be near Bermuda. I’ll look into this one more later, but at a first glance it looks like they have the forecast track wrong for this one. It looks like she’ll be north/east of the current track, passing well to the east of Bermuda. This may change in a day or so as she begins to interact with the outer areas of Isaac, but I’ll have to figure that out more carefully.

More later!

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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.

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