Friday, August 24, 2012

Tropical Storm Isaac Slow to Organize So Far; Will Be Much Stronger by U.S. Landfall...


Above is a recent visible satellite image of Tropical Storm Isaac. As of 7am CDT, the center of Isaac was located about 175 miles South/Southwest of Santo Domingo in the Dominican Republic.  This is also about 220 miles Southeast of Port Au Prince, Haiti. During the last 6-12 hours, Isaac has been  moving toward the West at about 15 mph.

The minimum central barometric pressure is 29.53 inches, and the maximum sustained winds are estimated at 50 mph.  The pressure took a healthy drop late yesterday evening, and as is usually the case, the increase in wind speed followed within 6-12 hours.

Although Isaac has been slow to organize thus far, the system should not be taken lightly.  Rapid intensification will be hard to come by as the system interacts with the rugged terrain of Hispaniola and Cuba this weekend, but a potentially dangerous increase in organization and intensity is likely when the system emerges over the very warm, undisturbed waters of the Gulf of Mexico late this weekend and early next week.  Unfortunately, this will allow plenty of time for the system to organize prior to reaching the U.S.



As mentioned in yesterday morning's post, NOAA threw a lot of hardware at Isaac yesterday in the form of numerous specialized aircraft missions into and all around the system.  All of this valuable data was fed into the computer forecast model runs at 7pm CDT yesterday and 1am CDT today.  As a result, the models are all coming into excellent  agreement insofar as the likely future path of Isaac, and the Westward trend has continued:

Computer model forecast tracks; Version 7pm CDT 8/23/12


Computer model forecast tracks; Version 1am CDT 8/24/12

The preliminary runs that just initialized at 7am CDT this morning also continue the same message of a northeast or northcentral Gulf Coast landfall: 


The National Hurricane Center (NHC) continues to forecast a landfall right down the middle of the model consensus, as shown in the latest advisory below:


Based on the present forecast, the center of Isaac would make landfall, as a hurricane, during the pre-dawn hours of Wednesday morning, somewhere along the Mississippi/Alabama/Florida coasts.  I agree with this general idea at this time, and we will be able to become even more precise over the weekend.

As I always stress in these situations, its important to remember that the affects of Isaac will be felt well away from the center (especially along the Eastern and Northeastern sides of the system).  For this reason, it is important not to focus solely on where that center will make landfall.

The issue of greatest concern to me at this point is that Isaac hasn't been very well organized so far, and I fear that folks may be taking the situation too lightly.  The waters over the eastern Gulf of Mexico are very warm and have been undisturbed since Tropical Storm Debby moved across the region in late June:


As I mentioned toward the top of the post, the very warm waters over the Gulf will allow for rapid intensification of Isaac once the center leaves Cuba early Sunday morning.  The center will then remain out over these waters all day Sunday, Monday and Tuesday, allowing for the expected organization and intensification.

Right now the "official" NHC forecast calls for Isaac to contain maximum winds of 85 mph at landfall.  I feel that this is a very conservative forecast based on the reasoning that I've described above.  In my opinion, folks along the Gulf Coast from southeast Louisiana to western and northwestern Florida should prepare as if Isaac will be a "major" hurricane at landfall, that way no stone will be left unturned in their preparedness measures.

Very heavy rainfall will be widespread in association with Isaac, with amounts in excess of 6 inches likely within the orange and yellow shaded areas on the following image: 


For the latest imagery and updates on Isaac, please refer to this dedicated webpage at our sister site, WeatherGuidance.com.  I'll also be posting updates here on the blog, facebook and twitter throughout the coming days as well.

For more information from the Original Weather Blog, including "live blogging" during rapidly changing weather events, please be sure to follow me on facebook and/or twitter:
 

1 comment:

Anonymous said...

thanks for share.