Saturday, August 29, 2015

Tropical Storm Erika: August 28, Update A

Even in California I am prepared for a Tropical Storm... having a sip of wine and thinking about the Cappuccino gelato in the freezer. ;-)

Tropical Storm Erika is looking a bit worse for wear this evening. They did shift her center, and she did stay on a more westward path today, so the entire forecast track shifted to the west and mostly outside the cone from yesterday. She is currently at 18.5N, 72.9W and is now heading WNW at 20mph. Here's the latest forecast track: 
This seems far more reasonable to me today as tracks go. Although difficult to see, I also think the location of her center seems to be more on target: 

They did also increase her winds to 50mph, but have brought her back to 45mph (central pressure 1008mb). I agree with the increased winds (possibly an underestimate), and also with the subsequent decrease in winds ... although I think her winds may be less than 45mph now. She is barely a Tropical Storm - mostly a bunch of rain clouds and strong thunderstorms (Keith L., I agree with you!): 

The reason she still looks like she's packing a punch is because she is interacting with the warm waters of the Caribbean - sea surface temperatures are 29-30 deg C, with the upper 150-175 m(!!!) warmer than 26 deg C just south of Hispaniola! There's the real source of convection and all that rain she is dumping over the Dominican Republic and Haiti. Haiti is, unfortunately, a tough place for this much rain by the way, because they are prone to mudslides. At the very least, I would expect the convection and thunderstorms to remain strong until she gets to Cuba.

I received a note from our intrepid on-the-ground reporter, Tom, on St. Thomas yesterday about the 'buckets' of rain she dumped there... "Here in north side of St. Thomas Not enough rain to fill a child's beach bucket." So, not quite as rainy as it looked like it might be and definitely not too windy.

There is a bit of wind shear and she is interacting with land, which will help to reduce her intensity. What will really help though is crossing Cuba along the length of the island (more or less) - like the path shown in the forecast track above. I am not sure if she will survive in any real form after that crossing, so she may not be too much of a problem for Florida. The thing to watch out for is how she fares as she crosses from Hispaniola to Cuba. As I said, there is some very warm water lurking in this part of the world. 

(ok, that's enough 'thinking' about the gelato in the freezer, it's time for some action... ;-)).

Looking at her circulation and the vorticity maps (see yesterday's post for a description) you can see that she is much weaker in the lower half of the troposphere now compared to the images I showed you yesterday. Here are her maps from 850mb and 700mb today: 

And here is her map from 500mb (the middle of the troposphere):

The bright red, well developed round 'splodge' from yesterday's map is not there now. Instead, at 500mb she is a longer 'swash' of yellow. A sure sign that she is structurally weaker - primarily due to interaction with land. 

I'll be back tomorrow, the anniversary of landfall for Hurricane Katrina, who was, 10 years ago today, an amazingly strong category 5 storm that dominated the Gulf of Mexico. 

Adieu until then,

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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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