Saturday, August 02, 2014

Tropical Storm Bertha: August 2, Update A

Itsy bitsy Bertha is barely a Tropical Storm. She could be downgraded to Blobette Bertha and hardly anyone would notice, but officially the NHC have kept her as a Tropical Storm with winds of 45mph, central pressure at 1010mb as a precautionary measure. They said they couldn't find a center of circulation (or closed circulation actually)... and neither can I - can you?:
(Sorry about the satellite video loop - can't be helped!)

She does have a bit of convection though, with maybe the odd thunderstorm or two (shown as dark orange patches), as you can see in this infrared satellite image:

I received an on-the-ground report from our intrepid reporter, Tom, in St. Thomas:

"Short update from St. Thomas...first drop of rain at 6:41am with expectations of 6" by days end. Newly cleaned empty cistern awaiting the incoming...gusty wind but nothing like St. Croix to our south must be getting. Cats are in their hurricane beds behind hurricane shutters dreaming of gold fish and swooping birds...Bertha is a breeze!"

Bertha is currently officially centered at 18.9N, 69.1W, heading WNW at 22mph. This is somewhat speculative because, as I said, no-one actually knows the center. She is weak for three reasons:
1. She is interacting with the Dominican Republic, Puerto Rico etc. as shown in the satellite images, and this interaction will weaken her a bit more.
2. She is also in that area of dry, dusty Saharan Air Layer that I showed you yesterday.
3. There is quite a bit'o'wind shear.

The convection is because the water is rather warm - sea surface temperatures are 28-30 deg C, and the upper 100-125 m is warmer than 26 deg C.

Her future intensity depends on how much she weakens as she crosses out of the Caribbean. It is possible that she will begin to strengthen again as some of those inhibiting factors go away... you can see that she is almost out of the dry SAL layer and is moving towards a low-pressure area which has already got convective activity (over the Bahamas) in this IR satellite image:

Wind shear also looks like it will weaken once she is in the Atlantic, and the water temperatures are as warm as those in the Caribbean. All things that will allow her to intensify. The track keeps her away from the US, but it looks like she will roll over the Bahamas (who are already getting a coat of water).

I'll be back with more on Itsy Bitsy Bertha 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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