This is the official blog for Bryan Norcross, Hurricane Specialist at The Weather Channel.
By: Bryan Norcross , 3:01 AM GMT on August 25, 2012
This evening 20 years ago the sun set on the horrendous first day after Hurricane Andrew. I was in downtown Miami at the studios of the NBC station. We knew that there was "total" destruction in South Dade County, but even that didn't describe it. Here's to the people that went through it... and held their families together in a situation that most people can't imagine.
And now there's Isaac. A number of developments today. It's organizing and intensifying... which would likely continue steadily and significantly if it weren't interacting with the landmass of Hispaniola. The system has a tropical-looking core for the first time, and the upper air pattern on the satellite imagery looks quite favorable. The intensifying trend will likely slow or stop, depending on how much land the core moves over.
Forecasting the exact track of the core and the intensity of Isaac is tricky. If the core of the system only passes over the narrow western Haiti peninsula and the eastern tip of Cuba, it will have more time over water and could be stronger than the NHC is forecasting. This is a case where the intensity is tremendously dependent on the exact track the core takes. We aren't able to forecast the minor difference in track that could result in a stronger storm when it approaches South Florida and the Keys. The NHC has issued a Hurricane Watch for the Keys for that possibility.
And then there's the forward speed. Isaac stalled today and is moving a bit more slowly tonight than it had been. Everybody in peninsula Florida needs to be ready for an extended period of heavy rain and strong winds - two days or more. In South Florida this begins late tomorrow (Saturday). Power outages and flooding in low-lying, flood-prone area are expected.
Another complicated issue, looking ahead, is the possibility of storm-surge flooding on the west coast of Florida. If the storm stays near the coast, after the center moves north of a given location and the winds come in from the southwest and west, the water will pile up along the coast and push storm surge into the rivers and bays, including Tampa Bay.
If the storm moves north farther offshore, like Hurricane Dennis in 2005, an effect called a "Kelvin wave" can set up in the relatively shallow water over the coastal shelf, which make the surge higher than it would be without that shelf effect. Just the right factors have to come together to get this enhancing effect, but it can't be ruled out. Whether Isaac is strong enough at that point so the storm surge is disruptive to the Republican Convention in Tampa remains to be seen... but based on what we know, it's going to be close.
All indications are for landfall on the northern Gulf coast as a Cat 1 or 2 hurricane, but there are too many moving parts to know exactly where that will occur.
See you tomorrow on the Weather Channel.
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