Wednesday, September 30, 2015

Hurricane Joaquin: September 30, Update A

Just time for a quick update. It's no surprise that TS Joaquin got stronger as he was already stronger than the official estimate I saw before I got on a plane yesterday. It looks likes the wind shear wasn't enough to keep him in place, and that vorticity signal I saw in the upper troposphere has also intensified which makes him a hurricane.

He is currently centered at 24.9N, 72.2W, moving SW at 6mph. Winds are 75mph, central pressure is 971mb. At 75mph, he is barely a cat 1 storm (range: 74-95mph), but I think this is still an underestimate, especially if that is his central pressure. That is quite low, which means that the winds will 'rush' in faster. The other indication that this is low is the vorticity (circulation) in the upper half of the troposphere, which is much stronger and better developed today than it was yesterday. Here's the 500mb level - which is the middle of the troposphere:
You can see a lovely red distinct splodge (technical term ;-)) at that level. Looking even higher, up to 200mb (about 10km above the earth's surface):
The 'red splodge' at those heights is now distinct from that larger red region to the northwest (a low pressure region), so it is really connected to this storm and not that system. This is what I would see with a hurricane. 

He is beginning to develop into a good looking storm with those lovely outflow bands, which you can begin to see in the visible imagery: 
I can't be sure that he had an eye overnight or not from this imagery. If he did, then his winds were closer to 90mph. I would place him as a storm with winds around 85mph at the moment. 

Fortunately the strong convection is not as spread out as the visible imagery would suggest, with those outer bands to the north being just clouds (blue in the infrared imagery):

The Bahamas are getting some rain, but the worst weather is offshore. Unfortunately, Joaquin will stay in that area for a while, so it will bring a lot of rain to the islands so they will have a rough few days. Also, the winds will be pushing water onto the northern sides of the islands, so expect storm surge! 

I'll try and pop back later today and check in on him.

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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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