Proud to be a weather-obsessed weather geek! \m/ Senior meteorologist at The Weather Channel. If not a meteorologist, would be a DJ ♫
By: Stu Ostro , 12:11 AM GMT on August 26, 2012
I don't think I'm exaggerating when I say that this is one of the more interesting tropical cyclones I've observed since starting to forecast them professionally more than 30 years ago.
It's been a big complicated mess meteorologically right from the start. During the morning weather briefing I lead at TWC, a few days ago I remarked that it seemed more like a monsoon depression than a tropical storm, i.e. one of those big gyres that occur in the western Pacific and Indian Ocean in which the sphere of influence is ginormous and the center is real broad rather than tight like in a tropical cyclone. (And at the time, aircraft recon was having trouble finding tropical storm force winds, thus my reference to a depression.)
At times throughout its life, Isaac has been fighting dry air and unfavorable upper-level winds, but at other times, especially when the outflow improved, it was hard to digest exactly why it was struggling to intensify, other than that huge systems tend to not spin up as quickly as tiny ones.
Finally Friday night, it started getting a tight core of convection, but it was then disrupted by land. Since then it has maintained a tighter center of circulation than a few days ago, but a new complication arose: a system to its west already producing locally heavy rain over South Florida and the Keys, and connected to Isaac (as well as to the feature producing heavy rain from North Carolina up across the Mid-Atlantic).
Image credit: UW-Madison SSEC
And, as the National Hurricane Center noted in their discussion, it is connected to another area of vorticity to the southwest of it.
Image credit: UW-Madison SSEC/CIMSS
Despite all of these complications, it has nevertheless managed to produce significant impacts, from flash flooding in Trinidad and Tobago and in Puerto Rico, and from flooding and wind in Haiti where fatalities have unfortunately been reported.
And now, by way of Cuba and the Bahamas, its large circulation takes aim on the United States, first in the Keys and the Florida peninsula and then the east-central part of the northern Gulf Coast. (Another interesting aspect has been the model track forecasts, and in particular the way the ECMWF's and GFS's have evolved, but that's a whole other topic!) Hopefully Isaac will remain a disorganized mess and relatively weak through its trek across the Gulf, but indications are that it'll finally be able to become stronger, and between that and its size, Isaac poses a serious threat.
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