Irma before even making landfall is at 155 mph for sustained winds. Let's say that the interaction of Irma with Cuba leads to a weakening down to 135 mph, which I don't think will happen, but let's assume. If that happens, Irma will still move back over the very warm waters in the Florida straights, we are talking about 85 to 89 degree waters that this storm will be moving over with little if any shear and still a very well developed core. With this being the case, Irma will have an excellent chance to rapidly intensify while up towards the west coast of Florida. As we saw with Hurricane Harvey just a few weeks ago, hurricane can rapidly intensify in just a few hours. As such, I would not be surprised if Irma jumps right back to category 5 status very quickly once back over the open waters on Saturday evening.
Look, let me address the previous ideas first. The forecast question has been and still is, when does that shortwave in the Mississippi River Valley tonight finally force Irma to start to turn? My concern the past few days had been and still is, when does this feature turn Irma northward. The models, yes even the ECMWF, was all over the place so it was important to give a heads up from the eastern Gulf Coast to Maine. Would I do that again? Absolutely. The key here is that you see the observations and adjust as quickly as the data supports the change.
So why still go with a turn to the north with such a large storm? Well, take a look at what is happening on the north side of Irma and over Florida. See how that stream of moisture is backing from a southwest to south-southwest component? What you are seeing is a developing steering current finally showing up, too late for that turn up the east coast of Florida, but not too late for the west coast. This developing steering current is due to that short wave in the Mississippi River Valley. The influence of this short wave will only increase. Now, due to the large size of Irma, the storm will not just move north on a whim, but will gradually turn from the current westerly direction to northwest and then finally north, being drawn right into western Florida and Georgia.
After Irma makes landfall, Irma will push into northern Florida and then Georgia where the storm will steadily weaken. The good news is that unlike Harvey, Irma and it's remnants won't be sticking around for long. The very dry air in place over the Tennessee River Valley and Southern Mid Atlantic will basically fall apart. While heavy rainfall is expected on up to the Tennessee River Valley, none of the heavy rainfall amounts seen in Harvey is expected at all.
Then we look at the next storms out there. We'll watch to see how Hurricane Jose lingers over the western Atlantic. There is a good chance that Jose will eventually be kick out over the northern Atlantic but that's not certain yet. Plus there is a potential for a strong Hurricane Lee developing over the next 15 days as well. The beat goes on.