Saturday, September 26, 2015

Tropical Depression Ida, the Caribbean Blob, and the Atlantic Blobette: September 26, Update A

Just popping in to check on how Ida and her friends are doing in the Atlantic and Caribbean. I see that she's still trying her best to hang on, but is now a Tropical Depression. 

Officially her winds are 35mph, central pressure is 1006mb. She does still have a closed circulation in the lower half of the troposphere, but she is not as well developed in the middle and upper parts of the troposphere, so a Tropical Depression seems about right to me. You can see her location and the closed circulation in the visible satellite imagery:

She is centered at around 24.3N, 47.4W, and is heading WNW at 5mph. You can also see that her convection is off to the east of the center and is struggling to get a foothold (it's been on a pattern of getting stronger/weaker/stronger/weaker):

It's to one side because of wind shear of course, and it's a bit wimpy because there is a spectacular amount of dry air all around her, as you see in this lovely water vapor imagery of the Atlantic:

So even if the wind shear drops (which it is expected to do), the dry air will stop her from growing too much. In fact, I think this will be my last update on Ida (unless something unexpected happens - and really, how often does that happen? ;-)).

Now, a quick note about a Caribbean Blob and it's friend, the Atlantic Blobette. You can see them in the water vapor satellite image above. 

One is in the region of Nicaragua, with quite a lot of convection just off the coast there, in the western Caribbean. The reason for the strong convection is because the sea surface water is over 30 deg C (phew... definitely balmy!), and the upper 100 - 150m of the water column is warmer than 26 deg C. We always see a lot of convection in this area for this reason. There is some circulation in the lower half of the troposphere, but it is interacting with land which is inhibiting the development of this system. It does look like it will move over water though (it's moving very slowly north-eastward) and away from land, which will give it a chance to get a bit stronger.

The second one is just north of the Bahamas. This one doesn't have much convection at the moment but again, there is weak circulation in the lower parts of the troposphere. 

The next name up is Joaquin. 

I'll keep an eye on both of these and if they look like they are going to misbehave, I'll be back. 

Ciao for now!

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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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