Thursday, August 23, 2012

Update on Tropical Storm Isaac...

Tropical Storm Isaac is moving Westward across the eastern Caribbean Sea this morning. As of 7am CDT, the center of Isaac was located about 225 miles South/Southeast of San Juan, Puerto Rico.  This position is also about 315 miles East/Southeast of Isla Saona in the Dominican Republic.  The latitude/longitude position is about 15.4 North/64.8 West.  Movement is toward the West at 13 mph.

Maximum sustained winds are estimated at 40 mph, with a minimum central pressure of 29.62 inches of mercury.

As far as thunderstorm activity is concerned, Isaac is a bit less organized this morning compared to yesterday.  This is likely a short-term situation, however, as the system is expected to encounter conditions that are more favorable for organization and intensification during the next 24-36 hours.  In fact, Isaac is expected to become a hurricane during the day on Friday.

Recent Visible Satellite Image of Isaac

As you can tell by the satellite images above, there is impressive "outflow" associated with the system at the middle and upper-levels.  As soon as the lower levels become better organized over the next 24-36 hours, Isaac is likely to become a formidable storm and/or hurricane.  Those in its path for Friday into the weekend should not take this situation lightly and are encouraged to continue on with their preparations.

Recent Infrared Satellite Image of Isaac

The center of Isaac is currently passing to the South of Puerto Rico by just over 200 miles.  A recent radar image from San Juan (below) shows most of the heavier bands of precipitation offshore to the South as you would expect.  Overall, the greatest impact on Puerto Rico today is likely to be higher than normal wave action and rip currents, with occasional passing showers or thunderstorms.

During the last 24 hours, the consensus of the computer forecast model guidance has shifted toward the West with respect to the eventual track of Isaac.  The latest composite image is shown below:

The National Hurricane Center (NHC) continues to go right down the middle of the model consensus, as shown on their latest track forecast below.  This forecast calls for the center of Isaac to ultimately pass just to the West of the Tampa Bay area sometime during the pre-dawn hours of Tuesday morning (as a hurricane):

The European (ECMWF) Model, which has historically outperformed the other computer models in forecasting organized tropical systems, continues to show a track further to the West, and is calling for a landfall along the Alabama/Florida panhandle coast on Wednesday evening:

Although the ECMWF solution is still further West than the consensus of the other models, even that model has shifted quite a bit to the East over the last 12 hours.  You may recall that yesterday the same model was forecasting a landfall near New Orleans, so it does seem to be shifting Eastward and is getting closer to coming into agreement with the "middle of the road" consensus track.

In an effort to improve the computer forecast model data, NOAA is throwing additional high-tech resources at Isaac today.  In addition to the regular "Hurricane Hunter" aircraft reports, several other types of aircraft will also be investigating the system (as well as the atmosphere for several hundred miles in any direction of it).  All of the valuable data that is gathered will be uploaded into the computer forecast models this afternoon and evening.  This will shed additional light on the system and its eventual track, and we are likely to see the forecast models come into even better agreement as the next 24-36 hours pass.

While gaining a better understanding as to the future track of Isaac is one thing, forecasting the intensity of the system is another.  The additional data gathered by NOAA aircraft today will also be helpful in improving the computer model's intensity forecasts.  As I pointed out yesterday, another key element to consider will be how much interaction the center of Isaac has with land over Hispaniola and Cuba on Friday and into the weekend.  Some of the mountains in Hispaniola reach 10,000 feet, and will do a good job of "working over" the system if it passes directly overhead.  While I fully expect Isaac to weaken back down to Tropical Storm level after passing over this region, it is likely to reintensify once again after getting back out over open water.  The question much will it reintensify?

The bottom line on the intensity of Isaac prior to any U.S. impacts will come down to how much time the center is able to spend out over water prior to making landfall.  The current NHC track would give it plenty of time over some very warm waters between Cuba and Florida for it to reintensify to hurricane strength prior to having any significant impacts on the U.S.  If the further West track of the ECMWF turns out to be correct, even more time would be spent over water, which would allow for even greater intensification.

I highly encourage all those living in Florida and the southeast U.S. (from Alabama through Georgia and the Carolinas) to continue to monitor the progress of Isaac over the next few days.  If you have already started taking your preparedness actions, that's great!  If you haven't, I highly suggest that you do so now before the "rush" gets underway and supplies become harder to come by.

While we still have several days to monitor this system prior to any impacts on the U.S., and the situation will become much clearer as early as tomorrow and Saturday, I always prefer to see folks start planning and preparing ahead of time, that way you don't have to panic when the time to take final action grows near.

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