The deep convection has really blossomed over the center of Isaac in recent hours. This is a sign that the stronger upper level winds are relaxing and that the dry mid-level air is being eroded away. Now, a much more unstable air mass is being tapped and Isaac is poised to strengthen, possibly to hurricane intensity.
As I mentioned in my last post, if we saw a burst of sustained deep convection, this could mean a rather rough day for the islands as Isaac passes through. The intense rain squalls that occur underneath such strong convection drag the winds down to the surface quite efficiently. I know from experience and the only good news here is that Isaac is not doing this as a major hurricane right now. So the next 24 hours or so will be quite tumultuous for portions of the Lesser Antilles and I hope people there are prepared and take it seriously. There is nothing quite like an intensifying tropical cyclone, no matter its initial strength. You can keep track of Issac’s progression through the region via Meteo France radar out of Guadeloupe by clicking here.
Once Isaac passes in to the eastern Caribbean, it is forecast to strengthen in to a hurricane. Just how strong it gets is up for debate. So many factors can shape the intensity of these systems that it is impossible to know for sure just how strong Issac will get. It would seem that with increasing ocean heat content and an apparently very favorable environment, that Isaac has the potential to become a strong hurricane before reaching Hispaniola. And that is a key milestone for the system and what eventually happens along the U.S. coastline.
The latest forecast from the NHC shows a track that would take Isaac over a good deal of the islands of Hispaniola and then eastern Cuba. If this does in fact happen, I would have to think that the rugged terrain would do quite a number on the circulation of Isaac and weaken it substantially. There are times when hurricanes have hit these land masses and never had time to fully recover. While this is great for interests further along in the forecast track, it would be terrible news for people on those islands. The threat of heavy rains and mudslides alone is enough to cause great concern. However, the geography is just right so that often times, the Greater Antilles have been the saving grace for many potentially deadly U.S. hurricane landfalls. Will that be the case again? I wish I knew. Let’s look at two models for some compare and contrast info.
First, the GFS. It has been doing pretty well this season and seems to have a good run to run handle on Isaac. It shows the system moving towards a break in the large high pressure area situated over the western Atlantic. This break or weakness would turn Isaac WNW and then NW at a point that would take it over the islands and possibly disrupt the circulation quite a bit. Obviously, the less land Isaac encounters, the less this disruption will impact the would-be hurricane.
On the other hand, the often praised for its superior forecast skill ECMWF model or Euro shows a weaker Isaac moving more west with time. It misses the big islands and turns Isaac in to the Gulf of Mexico as a formidable hurricane. In fact, the most recent run of the Euro was the western most forecast for Isaac yet, putting in to Louisiana in 10 days. I think we will have to watch and see one key element here. Does Isaac remain weak and get pushed along more by the lower level flow than it would if it were a deeper, larger storm in the atmosphere? Right now, it’s definitely growing in size in all directions. So unless it has issues getting stronger and extending up in to the atmosphere, I think the Euro can be discounted for now. Thus a threat to Florida, after Isaac passes over Hispaniola and Cuba, is a real possibility.
The other scenario would be that the turn NW happens even sooner and Isaac crosses Hispaniola rather quickly with no land interaction in Cuba after that. This would pose a threat farther up the coast of Florida and possibly even the Carolinas. This cannot be ruled out – remember Irene last year?
Today will be about the Lesser Antilles and what impact Isaac has there. Once it clears the islands, we can focus more on possible landfall solutions down the road. There is a considerable amount of time still left for Isaac to track in a number of directions and be at a variety of intensities. The best course of action for people in Florida is to just be on alert, check your generators, make sure you can put your hurricane plan in to action if needed. Just do the things now that can help make things a little less stressful should Isaac come your way. It has been seven years since any hurricane has hit Florida. A lot of people have no hurricane experience at all. Isaac might break the drought but it might not, we will just have to wait and see as hard as that may seem.
Meanwhile, invest area 96L out in the eastern Atlantic continues to become better organized. It should become a tropical depression later today and eventually TS Joyce as it moves westward across the deep tropics. There is no cause for alarm with this system just yet. Let’s deal with Isaac right now before worrying too much about a future storm. The east Pacific is nice and quiet.