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Storm Prediction Improving but Not Perfect

Small Shifts Can Have Big Consequences, as Punta Gorda Residents Learned

By Rob Stein
Washington Post Staff Writer
Sunday, August 15, 2004; Page A12

Hurricane Charley's sudden increase in intensity and unexpected path illustrate how difficult it remains for scientists to predict the track of the massive storms and precisely forecast their often inscrutable behavior, experts said yesterday.

"Predicting the overall track of a storm, we've gotten a lot better at that," said Richard Pasch, a hurricane specialist at the National Hurricane Center in Miami. "But when you have a big coastline, and it's a very strong storm, even the most subtle changes can have a big impact."

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Because Charley was expected to hit land closer to Tampa, many residents around Punta Gorda, Fla., were caught unprepared, prompting criticism from some local officials.

Improvements in computer models, a more sophisticated understanding of the internal dynamics of hurricanes and the winds and other forces that steer them, and better data from satellites and hurricane-hunting aircraft, have enabled forecasters to significantly improve their predictions in recent decades, experts said.

"Over the past 10 to 15 years, the improvement in predicting the track has been quite tremendous," said Hans Graber, a professor of applied marine physics at the University of Miami. "In the old days, the uncertainties were on the order of 100 to 200 nautical miles. We wouldn't even have known if Charley was going to hit on the west coast or east coast of Florida. Now we're less than 50 nautical miles."

Despite such advances, however, the magnitude and complexity of hurricanes and the multitude of factors that influence their behavior continue to vex forecasters.

"Mother Nature is very fickle," said Christopher Velden, an atmospheric scientist at the University of Wisconsin at Madison. "There's so much out there that remains beyond human prediction."

Hurricanes can, for example, careen off a predicted course because of relatively small alterations in the atmospheric winds that guide them.

"You can think of a hurricane as a piece of wood in a river," Velden said. "The hurricane is embedded in a steering current, which controls its direction, like a current in a river controls which way a piece of wood goes. Small eddies in the current can change the course."

At the same time, other weather systems also influence the storm's direction.

"There could be a high pressure system that would block it so it wouldn't turn to the north, for example," Graber said. "Depending on where these systems are placed, they can help pull a hurricane in a direction or block movement of a hurricane."

Events occurring inside the storm, which often elude satellites or tracking planes, can also affect the path.

"Subtle changes in tracking can be controlled by processes that can occur in the inner core of the hurricane, such as changes in thunderstorm activity inside the storm, and those can't be measured," Pasch said. "There's lots of interactions that occur there."

Predicting a hurricane's intensity is even more difficult than predicting its path, experts said, and sudden changes in intensity can alter a storm's direction. For example, higher ocean temperatures can cause hurricanes to suddenly intensify, as Charley did. A sudden intensification can, in turn, affect the winds around the storm -- and the smaller storms within the hurricane -- all of which can change the path, just as change in a piece of wood floating down the river can affect the currents and eddies around it.

"You imagine a hurricane being embedded in a river. As it grows it modifies the particular circulation in that river. That can make it difficult to predict," said Charles Konrad, an associate professor who studies hurricanes at the University of North Carolina at Chapel Hill.

One of the biggest shortcomings of modern prediction is often the inability to gather enough data quickly about a storm in real time since there are only a handful of planes available to fly close to storms.

"The hurricane hunters don't fly 24 hours a day around the globe -- there aren't that many planes available," Graber said. "You don't have continuous measurements. You may just miss key moments when something changes."

In addition to getting better data from planes, scientists are also trying to gather better information from satellites, perhaps by using different types of instruments.

"Most of the satellites gather measurements in the infrared. But they can't see below clouds," Velden said. "We've been using new tools in the microwave that we can see structure underneath like thunderstorms."

The National Hurricane Center's Pasch acknowledged that techniques need to improve.

"We still have to get better -- 90 percent isn't good enough. We have to get to 95 or 98 percent accuracy," he said.


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