Max Mayfield: Isaac's intensity forecast varies

National Hurricane Center issues intensity forecast for Isaac

By Max Mayfield - Hurricane Specialist
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PEMBROKE PARK, Fla. - All reliable computer model forecasts continue to show the future track of Tropical Storm Isaac heading in the general direction of Florida. Hopefully by now, most people understand that the track forecast will not be perfect. 

Forecasters are very aware of the uncertainty involved in track forecasting and that is why the so-called "cone of uncertainty" was created. 

The latest track forecast from the National Hurricane Center has shifted the track very slightly to the west as it approaches Florida. But, this current track, if it verifies, will have direct impacts on South Florida, including the Keys.

The response to Isaac that will be recommended by local officials will depend on the exact track, the intensity, and the size. There are uncertainties with all of these parameters. 

The NHC has been issuing very consistent track forecasts so far. It is important to know that there is tremendous uncertainty in the intensity forecast as well. Based on Thursday's 11:00 am forecast, the closest point of approach of the center to South Florida will be on Monday morning when Isaac is forecast to be a Category 1 hurricane.

To deal with the uncertainty in intensity forecasts, the NHC issues an Intensity Probability Table with each forecast. 

The probabilities at various time periods are based on forecast errors during recent years in the official track and intensity forecasts issued by the NHC. The current table indicates that Isaac only has a 2 percent probability of being a major hurricane (Category 3, 4 or 5) at the time of its closest approach to South Florida. The probabilities at this time are much higher for Isaac to be a tropical storm or a Category 1 or 2 hurricane.

We still need to remember that a hurricane is still a hurricane.  Even a Category 1 hurricane can cause damage and loss of life and that is why I never refer to a Category 1 as a minimal hurricane. South Floridians need to pay close attention to the updated forecasts and be ready to heed the advice of local officials.

And remember that the winds, rains, storm surge and tornadoes can extend well out from the center. These impacts will begin well before the closest point of approach of the cyclone's center. Don't focus only on the track.

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