LRandyB's Tropical Weather Discussion

The obvious story this morning is Gustav but it's not the only story to talk about. Let's look at newly upgraded Tropical Storm Hanna first.

There are a number of factors that will impact the future of TS Hanna. The first and most immediate is the upper level low sitting just to the west of Hanna. Current satellite shows that the circulation around that upper low is indeed shearing Hanna from the west, dampening or outright killing outflow on the west side of Hanna. NHC indicates that the low level circulation of Hanna is on the west side of the convection as a result of this shear. So the real question is how the ULL and Hanna will interact. The models seem to indicate that the ULL low will track west-southwest away from Hanna but looking at this morning's water vapor loops, the ULL is stubbornly stationary even as Hanna moves west toward it. If that trend continues, it will undoubtedly hinder development of Hanna. Another factor in the future of Hanna is the trough on the east coast. As it moves east, it's posssible that Hanna could be picked up and pushed northeast into the open ocean. At least one model forecasts this outcome but most expect Hanna to continue northwest and become a hurricane over the next 3 days before the trough passes her by and she meanders at the end of the forecast period. At the moment I am inclined to believe that the trough will indeed pass Hanna by and allow her to continue a westward motion. So we'll have to see if the ULL to the west of Hanna starts moving out away from her.

Now for Tropical Storm Gustav. The mountains of Haiti helped to reduce Gustav to a TS over the last couple of days. I think the new, more southerly position this morning is due less to motion and more to the mountains disrupting the circulation of Gustav and allowing a new center to form further south away from the mountains. But the interpretation by the models of the southerly motion means that the models shifted their tracks in the Caribbean further south and consequently, the long range tracks moved further west. The one model that has been more consistent than any I have seen in a long time has been the GFDL. Even as the other models were moving back and forth and varying in their degree of agreement, the GFDL has remained quite stoic in it's resolve to bring Gustav right here to my doorstep. And that model is generally considered one of the better models. But even that model is only as good as it's initialization and that is difficult with a stationary or meandering system and certainly with a weak system. But if Gustav establishes a steady direction and speed trend, the models will stabilize and give us a better idea of the long range outlook. Satellite loops as of right now do show Gustav's outflow clouds surging noticeably toward the west-northwest and I would expect that trend to continue. I expect you'll see a trend in the models today and tomorrow to shift Gustav's long range track more to the east but how far east will depend on how strong the ridge is in the Gulf and how much of an impact the weakness in the ridge will have on the track.

As always, and as indicated by NHC, it's pointless to focus on the long range landfall point but rather you have to focus on the area impacted in 5 days. As I said before, if you live on the Gulf coast, you should be ready for this storm.