Hurricane Alex, first of 2010 season, heads for Texas, Mexico
Hurricane Alex, after slamming Belize as a tropical storm Thursday, was declared a hurricane Tuesday evening. New extended hurricane warning rules are meant to give more precise, earlier warnings.
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Alex also marks the first Atlantic storm against which forecasters are giving county and city officials longer lead times for watches and warnings, notes Chris Landsea, the science and operations officer at the National Hurricane Center.Skip to next paragraph
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Until now, the National Hurricane Center issued a hurricane watch when a storm was 36 hours away and a warning when the storm was 24 hours out. Now watches are posted with 48 hours of lead time and warnings with 36 hours' lead time.
"Our definition of hurricane watches and warnings had not changed in three decades," he says. "But when you look at our predictions of where the hurricane is going to be, we've had a tremendous improvement in our skill."
Twenty years ago, a two-day track forecast had a 200-mile range of error, he says. Today, it's 100 miles. At the same time, the number of people living along vulnerable coastlines has mushroomed, a trend that keeps local emergency mangers awake at night thinking about evacuating people from popular but fragile barrier islands or other locations with limited evacuation routes.
In meetings with emergency managers, it became clear that watches and warnings under the old scheme were coming too late to be truly useful. to those officials who base their evacuation decisions on them, Dr. Landsea says.
"We didn't want them to become irrelevant," he says.
As the hurricane center gives its new approach its first application to Atlantic hurricanes, researchers are hoping to give forecasters even longer leads by allowing them to identify which "tropical waves" – seemingly haphazard assemblages of storms that can eventually evolve into tropical cyclones – are most likely to form tropical depressions, which can go on to form tropical storms and hurricanes.
The project is dubbed PREDICT – a month-and-a-half-long effort to take the measure of tropical waves as they form off the west coast of Africa.
The difference between the tropical waves that fizzle and those that grow into more-serious storm systems seems to lay in what goes on in the heart of the wave. Waves that seem to form a circle-the-wagons closed circulation at their centers seem to be the storms that most often blossom into tropical depressions, the immediate precursor to tropical storms and hurricanes. That closed circulation appears to stave off storm-stiffling dry air that can come in from outside the system. That circulation also appears to concentrate the warm, moist tropical air on which tropical cyclones feed toward the heart of the storm system.
The challenge, Dr. Davis says, is to make sure that's the mechanism, then try to identify the drivers behind it. If researchers are successful, it may eventually be possible to begin providing tropical cyclone forecasts perhaps as far as seven days in advance.
The project also has a short-term payback, Landsea adds. The research aircraft flying through the tropical waves to gather measurements will give scientists and forecasters at the hurricane center a rare look at conditions inside these waves. The waves tend to form too far at sea for hurricane-hunter aircraft to reach on a routine basis.
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