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Fine art of hurricane tracking: Push is on for the 7-day forecast

NOAA currently forecasts the paths of storms five days ahead. But scientists hope to identify storm systems sooner and better predict when one is poised to intensify – thereby improving hurricane preparedness.

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From a storm "genesis" standpoint, data from Karl may be a gold mine, says Ed Zipser, a researcher at the University of Utah. He notes that scientists were able to fly through the system for four days before it strengthened enough to reach tropical-storm status.

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But those first four days present a puzzle. During that period, the stormy region that would become Karl had all of the conditions necessary for a system to organize and strengthen: warm seawater at the surface; a vigorous preexisting weather disturbance; weak changes in wind speed and direction with altitude; lots of moisture in the air; and lots of towering, thunderheadlike clouds dumping heavy rain.

Yet only on the fifth day did the storm cross the tropical-storm-to-cyclone threshold. Before that, the storm alternated between day-long flare-ups and day-long interludes, says Dr. Zipser. The data that tracked this phenomenon, he says, may hold clues to subtler factors that must be present for a storm to earn a name.

To continue looking for these clues, NASA is funding scientists to deploy two of its Global Hawks – which can reach altitudes of 55,000 feet and stay airborne for some 30 hours, gathering key information on a storm for far longer and far more frequently than satellites or piloted aircraft. The three-year program begins next year.

A key piece of information the drones are likely to hunt for: the status of ice crystals in the thunderheads near a storm's center. Changes in the concentration of ice crystals high in these clouds could signal the coming of a rapid increase in intensity, recent research suggests.

Why ice crystals?

The more ice high in these clouds, the stronger the updrafts pulling warm, moist air from lower altitudes to feed the storm. From a bird's-eye view, this ice buildup looks like a bright ring around storm centers just before rapid intensification.

University of Illinois atmospheric scientist Stephen Nesbitt and graduate student Daniel Harnos conducted a systematic search of microwave data from satellites from 1987 through 2008 and found many more examples. A ring formed about six hours before a storm underwent rapid intensification. Then, as a storm continued to intensify, the ring tightened.

They also found that this signal in the ice crystals came in two forms, depending on the broader atmospheric conditions a storm was encountering.

The data could lead to a new tool for predicting rapid intensity changes within the next two years, Mr. Nesbitt says.


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