99L improves slightly

During the 8 o’clock hour on the east coast of the US, the NHC issued an increased outlook on 99L, saying that with marginally favorable conditions the area of low pressure now has a 50% chance of developing into a tropical cyclone. 99L has winds of 25 mph and a pressure of 1009 millibars with movement to the west at 15 mph.

A look at any satellite image this evening would yield a preliminary appearance of improvement from yesterday, however as you can see below the center of circulation is to the east of most of the stronger thunderstorms, which is due to mid level winds blowing out of the east toward the west at 30-35 mph. Conditions took just a small notch backward today, but it does seem that overall organization at the surface did improve. Earlier scatterometer passes showed meagerly better cyclonic spin at the surface and surface temperatures continue to creep up. Saharan air seems to be staying out of 99L with the entire basin clearing of the dry air. You can see that drier air, or what is left of it, in the darker grays to the NE of the center, which is encircled in black.

Each of the model runs today have adjusted to the slightly less favorable conditions lowering their day 2-5 intensity forecasts and nudging their respective forecast tracks a bit farther south. Looking first at intensity, which will guide track, the forecast remains generally the same as yesterday.  With the slight step back from yesterday, i’ll slightly push back my forecast for an upgrade to tropical depression to sometime on Thursday with tropical storm status being attained Friday. The next name on the list is Ernesto. I believe Ernesto will reach a maximum near the islands of 40-45 mph before getting into the eastern Caribbean on Saturday. Less favorable conditions in the eastern Caribbean will greet Ernesto, which if the models are correct will slow any intensification.

Going back to track forecasting, the models have pushed a bit farther south with almost every model moving 99L into the Caribbean. My early forecast would put the system between Tobago and Antigua on Saturday morning. I’m leaning toward the southern two-thirds of that zone, but if the system intensifies beyond 45 mph (which is possible) it will track to the north. I am forecasting a Caribbean Cruiser from there with only modest intensification at best. The Bermuda High will keep 99L/Ernesto on a just north of W to WNW track through the western Atlantic and Caribbean. Below is the early cycle 00Z spaghetti model plots:

I’ll start talking about impacts tomorrow, but readers in the Lesser Antilles should be preparing for a strong tropical wave/weak tropical storm. You should not wait for this system to be named to prepare. The first likely recon flight will occur on either Friday or Saturday, and I’ll be watching that.

I will be updating on twitter @JonathanBelles over the next few days on both Florida weather and this system.

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Posted on Tuesday, July 31st, 2012, in Florida Weather, Severe Weather and tagged , , , , . Bookmark the permalink. Leave a comment.

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