Wednesday, August 22, 2012

Tropical Storm Isaac Becoming Better Organized; Eventual Southeast U.S. Threat?

I've been reserving comment on what is now Tropical Storm Isaac for several days. Those of you that have e-mailed or direct messaged me on twitter or facebook have received a reply with my initial thoughts, and as I pointed out, I typically try to wait until we get a better handle on the situation before making a general post when it comes to tropical systems, as the uncertainty level is relatively high in most cases (and I try to avoid jumping on the "hype bandwagon" when possible).

With that said, Isaac is definitely "there" and is becoming better organized.  This, along with a better emerging idea as far as the eventual track and potential impacts on the U.S. warrant the initiation of coverage here on the blog...

A recent infrared satellite image of Isaac is shown above.  The system has become better organized overnight, with convection (thunderstorm activity) increasing in virtually all quadrants around the center of the storm.

As of 7am CDT, the center of Tropical Storm Isaac was located 210 miles East of Guadeloupe (15.7 North, 58.4 West), and moving West at 19 mph.  This general motion is expected to continue for the next few days.  Maximum sustained winds were 45 mph and the minimum central pressure was 29.65 inches.

Isaac is forecast to intensify over the next 48 hours, and is likely to become a hurricane sometime tomorrow.

Based on the present location and track, the center of Isaac will move through the Leeward Islands this evening and then out into the northeastern Caribbean Sea tomorrow.  The latest "official" forecast track from the National Hurricane Center (NHC) through Friday night/early Saturday is shown below:

Hurricane Watches have been issued for the areas in pink on the above image, with Tropical Storm Warnings shown in blue (including Puerto Rico, where at least Tropical Storm conditions can be expected most likely on Friday).

Beyond the 3 day forecast, the situation becomes less clear insofar as exactly what Isaac will do.  The latest composite image of the computer forecast models is shown below:

As you can see, the "average" track of the computer models calls for a turn toward the Northwest and a potential impact on Florida late this weekend or early next week and possibly other portions of the southeast U.S. coast shortly thereafter (early to midweek).  This trend is reflected by the "official" NHC forecast which currently extends out through the pre-dawn hours on Monday:

The present model consensus and NHC track forecast is supported by climatology, which shows that the majority of tropical cyclones that originate where Isaac did at this time of the year typically take a track through the Caribbean, the Bahamas and sometimes affect adjacent portions of Florida and/or the southeast U.S.  The tracks of 9 storms that are most similar to Isaac (with respect to the location and time of initiation) are shown below:

As we showed earlier on the 3-day NHC track image, the center of the system is currently forecast to move over the Dominican Republic late Friday and early Saturday.  If that forecast verifies, the rugged terrain in the region will take a toll on the system, but it could then reintensify when it moves back out over water (however this also depends on what interaction may take place shortly thereafter with Cuba).

It is noteworthy that the European Model (ECMWF) is a major outlier, and continues to forecast that the system will move into the Gulf of Mexico and then make landfall along the middle Gulf Coast toward the end of next week:

The ECMWF solution is definitely "way out there" at this point, and we'll have to monitor conditions over the next few days before we can determine whether or not such a scenario appears realistic.  At this time, conditions and climatology favor the more Eastward tracks that were shown further above.

At this point my advice would be that anyone living in Florida and the southeast U.S. (i.e., Georgia and the Carolinas) should keep at least a casual eye on the progress of Isaac over the coming days. We'll have an even better idea by Friday and into Saturday as to exactly what is likely to transpire with the system for early next week.

If you live in these areas, it wouldn't be a bad idea to go ahead and take a few minutes to review your Tropical Weather Preparedness Tips, which includes preparing a safety/survival kit and identifying the best plan for an evacuation route if that becomes necessary.

While there is certainly no need to "panic" in the southeast U.S., it is never too early to prepare just in case - that way you avoid the rush once a more clear path comes into view (which is often when everyone else decides to react, usually at the same time).

For all of the latest satellite and (where available) radar imagery concerning Isaac, be sure to check out the dedicated page on our sister site  I'll also be posting updates on the blog, facebook and twitter as the situation unfolds as well.

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