Tropical Depression 9 has been reclassified as Tropical Storm Isaac this evening by the National Hurricane Center. Hurricane Hunters found 44-knot (50.6-mph) winds at flight level just to the northeast of the center of circulation, according to the NHC’s 5 PM discussion. Satellite estimates also had the surface wind at nearly 35 knots (40.3 mph). The minimum central pressure was at 1005 mb as it moved westward at nearly 17 mph.
Isaac’s circulation looks good on the last visible satellite loops available. Convection looked pretty good earlier, but has seemed to die down and now looks a little less organized in the last few frames on the infrared satellite loop. The water vapor loop shows drier air ahead of and to the north of the TS, but dry air doesn’t seem to be intruding as much as it was last night. The GFS has shear to the northeast of Isaac in about 24 hours, so the shear Isaac has been experiencing should die slightly down over time.
Isaac will move into the Lesser Antilles on Wednesday and move west and west-northwest away from the islands on Thursday. What happens after nearing Puerto Rico and the Virgin Islands, and affecting Hispaniola and possibly Cuba? Well, there’s been a lot of hype on social media on that.
For the last day or so, the GFS (and its ensembles) have been eyeing The Sunshine State. The European model was leaning with the GFS last night. Today, more models are pointing towards the state. Now, does it make the forecast etched in stone? Absolutely not. The media have been flooding social networks with headlines along the lines of “storm will hit Florida.” Even some have been saying it will impact Tampa and possibly affect the Republican National Convention. Let’s keep in mind that these are guidance models, hence the word “guidance.” Meteorologists use models to help determine a forecast, not solely base their forecasts off of them. There are many factors that could change this forecast and I will briefly discuss a few…
- The latest model runs likely don’t have the Hurricane Hunter data ingested yet. The big problem with tropical systems is that surface and upper-air data are scarse. This leaves little data to be plugged into the models and help create accurate forecasts. We’ll see if the forecast tracks change in a couple of runs.
- Any rapid changes in intensity, slow intensity increase, or even if the storm’s intensity stagnant, this could alter a forecast. If a tropical cyclone (TC) is weak, then the storm will be directed more by low-level flow. If the TC is very potent, then the storm will be directed more by upper-level patterns.
- Strength is also dependent on where it goes. If Isaac goes over the island of Hispaniola, for instance, the mountainous terrain could weaken it. Even if it still makes a b-line for Florida, it might not be as strong as some models are hinting at.
- The storm is roughly six days away. I have seen models for TCs remain consistant on a track and then everything flips on its head in the end.
I am not downplaying the risk of Isaac at all – it needs to be watched carefully. But having the media and even a few meteorologists hype it up and already calling the shots six days out is, in my opinion, irresponsible.
Everyone from the Carolinas to the gulf coast should check in periodically for the latest info on Isaac.
11 PM EDT Update: Tropical Storm warnings are in effect for Puerto Rico, the US and British Virgin Islands. The governor of Puerto Rico has already declared a state of emergency for the island.