Saturday, August 17, 2013

Tropical Storm Erin and the Gulf of Mexico Blob: August 17, Update A

Friday night. Wine. Cheese. Wine. Dinner. Wine. Friends. Wine. Wine. More Food. Ice Cream (Pineapple Upside Down Cake Ice Cream!!)  Wine. Result: a rather entertaining evening and quick(ish) update. J


Tropical Storm Erin

The NHC decreased her to a Tropical Depression earlier today with winds of 30mph, but she's back up to being a weak Tropical Storm with winds of 40mph (TS range: 39-73mph), central pressure estimated to be 1006mb. I agree with her TS status. She is officially at 18.5N, 34.5N (it looks like both I and the NHC were a bit off in her track forecast yesterday). It looks like she is tracking a little east of the current center of cone estimate (maybe around 18.5N, 33.5N), so I wouldn't be surprised if her forecast track is moved slightly northward.


Her convection did take a bit of a hit today, but it has been on the increase over the last few hours. The NHC forecast keeps her as a weak storm with winds of 40mph, and by this time tomorrow they think she will be a Tropical Depression and deteriorate from there. This is quite possible. Although she is currently moving over waters of about 25-26 deg C (too cold to sustain her in the manner she is accustomed to), it looks like she will shortly move over warmer waters with surface temperatures of 26-27 deg C, and that water will be warmer than 26.5 deg C in the upper 50-75m of the water column. This warmer water will help keep her going. However, the atmosphere holds two potentially inhibiting factors in her future:  there is dry air to her west and the wind shear will increase quite a bit - both good reasons for her to weaken tomorrow.


Gulf of Mexico Blob

This little blob looked like he was going to fizzle out fairly quickly but there may be a bit of a hiccup in the making. Instead of zipping across the southern Gulf and into Mexico, he is currently stuck. There is some circulation throughout all levels of the troposphere, however there is also some wind shear from the southwest, so his center is in two different places depending on how high you look in the troposphere: It is either at 20.9N, 91.6W (low level) or at 22.5N, 90.5W (upper level). Another big inhibiting factor is the dry air to his west:



Sea surface temperatures are 29-31 deg C, which is definitely warm enough for him, with waters warmer than 26.5C in the upper ~50m. Officially the NHC give him a 40% chance of development, but they may increase this a bit tomorrow if he doesn't get his skates on! Stationary storms are always a little trickier to forecast than the usual tricky storms because while they are sitting there enjoying the view, the pressure fields around them are changing which means their track may not be as forecast. Hopefully this sitting around business is just for a handful of hours.  


That's it for tonight. I'll be awake and back tomorrow.




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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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