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Hurricane advice from an expert

Storm track predictions are better, but there’s still a margin of error, and intensity can change quickly

Storm track predictions are better, but there’s still a margin of error, and intensity can change quickly

When talking about hurricanes, meteorologist Steve Letro is fond of quoting the Heisenberg principle, which in quantum mechanics leaves no room for certitude.

“Uncertainty is always going to be there,” said Werner Heisenberg, an early 20th century physicist, about predicting the motion of subatomic particles. The same could be said for predicting hurricanes, says Letro, head meteorologist at the National Weather Service in Jacksonville, Fla., and a liaison for the National Hurricane Center in Miami. “Errors are inherent in it,” he says.

The average error in the 24-hour hurricane forecast track was about 88 miles in 2003. That means the track veered on average 88 miles from the one that was forecast 24 hours earlier. Today that average error is 70 to 75 miles.

Forecasters have cut track error in half over the last 15 years, and they continue to improve on that at a rate of about a mile a year. “Which means in 70 or 80 years we’ll be really good at it,” says Letro, who spoke to 160 participants at the Marine Hurricane Preparation Symposium in Orlando in March. Sponsored by BoatU.S. and Florida’s marine industries, the symposium gave boatyards, marinas, yacht clubs and boaters information on how to prepare for a hurricane.

Letro says forecasters actually are getting pretty good at forecasting hurricane tracks. However, they are not nearly so good at predicting a storm’s intensity. “They can measure strength, but they can’t predict it 24 to 48 hours out,” he says.

Forecasters understand pretty well the internal structure of hurricanes, but they don’t have a handle on the so-called “eyewall replacement cycle” — how eyewalls contract, dissipate and form new eyewalls. That represents a big unknown because hurricanes reach peak intensity when their eyewalls contract.

The difference between a Category 2 hurricane (96 to 110 mph) and a Category 4 (131 to 155 mph) is huge, as folks in Punta Gorda, Fla., learned Aug. 13, 2004, when Hurricane Charley did just that in three hours, reaching peak intensity (150 mph) only two hours before landfall. The strength of the storm was a surprise, Letro says, but its strike in Punta Gorda should not have been.

The forecast track showed Charley hitting the Tampa area, but the hurricane was paralleling Florida’s west coast, and when a storm does that a potential track error of 75 miles extends the range of landfalls some 600 to 700 miles along the coast. Coastal Florida, from the Keys to north of Tampa-St. Petersburg, had been under a hurricane warning for 36 hours before Charley went ashore at Cayo Costa Island — about 75 miles south of Tampa — and went on to tear through Punta Gorda.

Many in Punta Gorda and surrounding areas were unprepared for Charley, let alone a Category 4 Charley. Letro reminded his audience that the forecasters aren’t that good at predicting intensity, but they were on the money with the warning they issued for Charley. Everyone from the Keys to Tampa was vulnerable to that storm and should have been on high alert.

Letro’s account of the Charley experience brought his sternest warning of the day. “Concentrate on the warnings, not on the forecast track,” he says. “I don’t like the tracks being out there. I wouldn’t give an electric skill saw to a 2-year-old. I wouldn’t give these track forecasts to the public.”

Letro says coastal residents should base their preparations on the hurricane warnings that the National Hurricane Center issues and the coastal areas those warnings encompass, not on the tracks, because the tracks can be wrong. He warns, too, that the graphic depictions of wind fields in weather reports are at best rough approximations of how strong the winds are and how far from the center they extend, because the winds come in bands that are constantly changing and evolving with the eyewall. Wind bands may come much earlier or later than the time frame suggested by the wind-field graphics, and may be stronger or weaker than those forecast.

“These programs are designed to give you an idea,” Letro says. “They are not to be taken literally. They are dependent on the [actual] track and the evolution of the eyewall bands.”

Finally, Letro advises boaters and marina, boatyard and yacht club operators to be discerning about seasonal forecasts. Colorado State University’s early 2008 forecast for the June 1 to Nov. 30 Atlantic hurricane season calls for 13 named storms, seven of them hurricanes and three of the hurricanes Category 3 or stronger. According to the forecast, the probability of at least one major hurricane hitting the U.S. coast this season is 60 percent (compared to the average for the last century of 52 percent) and 37 percent for the U.S. East Coast, including peninsular Florida (compared to 31 percent for the last century).

Letro says actual landfalls will depend on where the steering currents that influence hurricane tracks happen to be when the storms form. Last season, 15 storms were predicted, and while it was a bad hurricane season for Central Americans, it was a quiet one for U.S. coastal residents. The steering currents sent the storms into the western Caribbean.

“The thing about these seasonal forecasts is they make you think we know something about steering patterns in hurricane season, but we don’t,” Letro says.

Don’t take the seasonal forecasts as gospel. Don’t base your planning on forecast tracks. Do take hurricane warnings seriously, and execute your hurricane plan when forecasters issue them for your area. Hurricane warnings give the forecasters’ best estimate of where the hurricane is likely to hit, taking into account potential error in the forecast track.

That’s the word from one of Florida’s top meteorologists.