TD 9 forms…new hurricane threat to the USA, Caribbean

Over the last few weeks i’ve been watching a disturbance roll across Africa, get invested, and continue to develop in the eastern Atlantic. Today, it was upgraded to a Tropical Depression…the ninth of the season.  In the heat of the Cape Verde season, this is a classical and climatologically normal system coming at a rather bad time for Floridians and politicians alike.

First, I want to talk about the facts and the warnings that are currently out, but I want to stress this is not a time to jump of your couch and go running out the front door that a hurricane is coming. TD 9 is currently located at 15.3N 53.2W or 580 miles E of Guadeloupe and is moving due west at 18 mph. TD 9 has a pressure of 1008 millibars and winds of 35 mph. Tropical storm watches and warnings have been posted, and are summarized in the graphic below:


Remember that a tropical storm warning means that winds of 40 mph or greater are expected within the next 36 hours. These conditions are also possible in the areas outlines in yellow and those areas may see an upgrade at any time as forecasts are refined and the cyclone moves westward. Hurricane watches may need to be issued tomorrow afternoon for areas from the USVI to points westward.

According to the NHC, steady organization and strengthening should occur throughout to-be Isaac’s lifetime until landfall somewhere in the Greater Antilles later this week. For those of you in the lesser antilles, you should be preparing for a weak category 1 hurricane, but at this time I think it will be a moderate to strong TS during the rendezvous with the islands. This is very well depicted by the global models and their consensus at this time. The hurricane models (GFDL and HWRF) keep this system weak throughout it’s lifespan, but I think they are having trouble latching onto the weak system. The hurricane model camp is very distinguished from the global models in that the difference is a clear 40 mph difference in intensity. All in all this is a pretty high confidence forecast. Tropical storm conditions will likely first be felt in Guadeloupe and Dominica early Wednesday morning with rain bands moving in much sooner. Moisture is already visible in the form of summertime thunderstorms on the Puerto Rican radar. I think bursts of thunderstorm activity will be persistant over the next few days, but there will be lulls in activity at times.

The upper level structure of TD 9 is very well formed with a clear anticyclone on top, which will enhance outflow later today. TD9 has plenty of moisture to work with and the dry air to the north should be kept out by the lack to shear. Strong shear is in place across the Caribbean, but with a well formed anticyclone aloft (shear sweeper so to speak) i’m not all that worried about it. In fact, the ships guidance from this afternoon shows a drop to nil shear in a couple days. I think that by the time TD9 gets to the graveyard that it should be well enough formed to escape any effects of dry air from south america. Td9 will be traveling over some of the warmest waters on this side of the globe as it moves across the Caribbean this week. Over the next few days I think the two faults for TD9 will be a warm upper level air temp (which limits thunderstorms) and early friction effects from Hispaniola in a few days.

I think in the long term, what will be Isaac will stay south of the DR and may flirt with Haiti before crashing into Cuba over the weekend as a category 1 or 2 hurricane.  In terms of CONUS landfall I think there will be landfall or at least a scrape in Florida early next week during the Republican National Convention, which will be held in Tampa/St. Petersburg next week. I’ll look at these possibilities later this week, but for now everyone across the Caribbean needs to be preparing for a strong tropical storm or hurricane.

There are currently seven hurricane reconnaissance flights scheduled aloft and at the surface for the next 48 hours, and I suspect more will be added as time allows. You’ll probably see an increase in US weather balloon launches and possibly an unmanned recon flight as well. If you have any flights down to the Caribbean this week, expect travel to be rough going this week.

Also, if you have any pictures of to-be -Isaac, send them to be @JonathanBelles on twitter so that I can share them with everyone.

Climatology Note: Since 2000, seven “I” storms have been retired…more than any other letter. And 7 of the last 11 “I” Storms were retired. Storm names are retired when enough damage or life is lost to change history of a certain location. Those retired storms were Iris, Isidore, Isabel, Ivan, Ike(which replaced Isidore), Igor (which replaced Ivan), and Irene. “I” just might stand for intense or infamous. Be aware of the I’s!

Personal Note: I’m now moved in upstate to Tallahassee to start my Master’s Degree in meteorology next week. I should have more time to update especially since I will be studying what I am talking about here.


I will likely update later tonight or tomorrow morning with information on the other two invests in the Atlantic right now, but the concern is with TD9 for now. If recon finds anything interesting i’ll update on twitter until then.  See you all soon!


Posted on Tuesday, August 21st, 2012, in Florida Weather, Tropical Weather. Bookmark the permalink. 2 Comments.

  1. jonathan…like your blog…im retired navy weather guy.4 years as hurricane weather man..fully retired live 8 months in fla and 4 months in upstate n.y.good luck in future endavors…..


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