Isaac organizing, TD10 develops - 8/22/12
Good afternoon and welcome to my tropical weather update for Wednesday, August 22nd, 2012. We are now dealing with organizing Tropical Storm Isaac entering the Caribbean and Tropical Depression 10 which is very likely to become Tropical Storm Joyce sometime within the next 24 hours. I am very impressed to be up to our 10th tropical depression by August 22nd. What is more impressive is the fact that it is an El Nino year. I'd have been less impressed if all these where from like cut off lows off the US East Coast like they where last year, or non-tropical in general. But every storm this month that has developed has done so from a tropical wave off Africa. That's usually a good signal for an active season.
Figure 1. Current satellite image of the two cyclones.
Forecast for Isaac
Looks can be deceiving, and Isaac is certainly a prime example of what I would call just that. From satellite, if this where out in the middle of the Atlantic this would be approaching hurricane status, however it appears according to recon that pressures are at a high 1006mb, and winds are only 45mph. This is exactly, once again what happened with Hurricane Ernesto, and it feels like we're talking about Ernesto all over again like we where a few weeks ago.
Figure 2. My personal satellite interpretation of the current situation.
I believe this a combination of the fact that Isaac is moving at 21mph, and there is dry air penetrating Isaac to the north. However, Ernesto was a very small system when it entered the Caribbean with minimal spiral bandings, Isaac is massive with impressive spiral bandings, this will defiantly help fend off any dry air in the Caribbean like Ernesto had to deal with. Once we begin to see deep spiral banding on the north side, that will be our hint for strengthening. Another factor is that Isaac's Upper Level Anticyclone (ULAC) is misplaced and that is allowing for some shear to becoming in on the northeast side. Unlike Ernesto which had issues with spiral bandings on the more critical West side, this will seal off as Isaac enters the Caribbean and become less of an issue.
Figure 3. Current CIMSS wind shear analysis.
The track is a difficult issue, I will be honest with you I have little idea where it will go after Haiti. A lot of storms that exit Haiti tend to experience a 'bump' westward that causes a shift west that could very well increase the threat to Florida and the Gulf Coast. The NHC is thinking along the lines of the models that this will impact Haiti as a Category 1 hurricane and weaken, then strengthening as it heads towards Florida, strengthening back into a hurricane. It's not hard to image what would happen if Isaac got into the Gulf as a hurricane as shear is low and there is SST's and TCHP that haven't been touched by a cyclone in peak season for many years.
Figure 4. Current forecast track for Isaac.
Tropical Depression 10 likely to strengthen
Our next area of interest is organizing Tropical Depression 10 off the coast of Africa, continuing the string of tropical cyclones developing the last few weeks. TD10 is no threat to land but does bare watching over the next few days. I suspect hat this will become Joyce and perhaps even approach hurricane status as the NHC is predicting it might do towards the end of the run. A lot of this depends on how large Isaac gets and how much that will have an influence on track and intensity. Right now, it is unlikely TD10 will approach the Caribbean as Isaac did.
Figure 5. Current satellite image of TD10.