Tuesday, September 22, 2015

Tropical Storm Ida: September 21, Update A

Distressingly little time for sloth or idleness today, alas! TS Ida has slowed down, and is now officially at 21.7N, 49.5W, moving NNW at 5mph. It is a bit difficult to see her center at the moment because it's night time (obviously! ;-)), and also because she appears to be a a bit disheveled. I think the center may be slightly to the south and east of the official location.

The NHC did increase her wind speed today, but have brought it back down to a very weak 45mph (Tropical Storm range: 39-73mph). I continue to think this is a bit of an underestimate (British understatement strikes again). There are a few clues that lead me to believe she is stronger than they think:

1. The vorticity (circulation) is stronger in the lower half of the troposphere than it was yesterday. For example... 

Yesterday's 500mb vorticity field: 
Today's 500mb vorticity field: 
See how much better formed (rounder and redder) she is? You too can look at the evolution of the circulation if you go to the University of Wisconsin page - at the top left are buttons that allow you to move back in time in 3 hour increments. (By the way, if you have forgotten how to get to this page, check out the <Science Alert!> here).

2. They claim strong wind shear. The wind shear is somewhere between 10-20 knots. Her winds are 45mph, which translates to about 40 knots. If this is really her wind speed, this means she is experiencing wind shear that is half as strong as she is. That would be really strong relatively speaking and she should have fallen to bits already!  

3. Oh, and then there's the convective activity. Does this really look like a system that is barely eking a living as a Tropical Storm to you? 
And looking at her on the larger Atlantic stage:
Yes, ladies and gentlemen, that big red blob that could swallow most of Florida is, supposedly, a very very weak Tropical Storm. Really?


So, to sum up: I agree with the NHC that she's slowed down and her name is still Ida. 

Until 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.

1 comment:

Mitch Roffer said...

What about the circulation just NE of Puerto Rico? Supportive or unsupportive of Ida's development?