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Forecasting Hurricanes: A Very Uncertain Business

FOR meteorologists, hurricane Emily provides an example of both the effectiveness and the limitations of the modern hurricane-forecasting system.

Meteorologists can spot such storms early and track their development for days. They can give timely warnings that allow possibly threatened coastal regions to prepare for a storm. Yet, as the American Meteorological Society warns, it would be a mistake to become complacent with this degree of effectiveness.

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In spite of radars, satellites, spotter aircraft, and computers, forecasters still cannot accurately anticipate a hurricane's changes in intensity, speed, or direction. Forecasting, the society says, ``remains rather subjective,'' and as coastal development continues, the society adds, this situation is not satisfactory. For one thing, it results in overwarning, causing costly and sometimes needless evacuations and other disruption. Yet, for now, such extensive warnings are the only safe course.

Weather scientists in the society are concerned enough about the state of hurricane forecasting to formally state these limitations. At the same time, they see ways to significantly improve their forecasting ability in this decade. In brief, they need both a better scientific understanding of hurricanes and a better ability to measure the characteristics of any storm they are tracking.

Hurricanes are the greatest storms on Earth. Because of this, they attract public attention. Yet, meteorologically, they are rare. Only a few of the many seasonal tropical disturbances ever reach hurricane strength. This year, forecaster William Gray of Colorado State University at Fort Collins predicts that there will be six Atlantic hurricanes. He expects two of them to be major storms. However, there will be many more tropical disturbances during the hurricane season, which runs from June through November.

The watchful eye of a weather satellite can spot an incipient hurricane early and track it long before it becomes a threat to land. Yet, the American Meteorological Society points out that satellite measurents can misjudge a storm's position by tens of miles and mismeasure its speed by tens of knots. Reconnaissance aircraft can improve the tracking data. Radar also helps when a storm is near land. But meteorologists still lack the full three-dimensional picture of a storm and the larger atmospheric environment they need for accurate track forecasting.

Computer simulations also greatly aid forecasting. Yet, they too, can let forecasters down. This is especially true of their occasional failure to anticipate sudden major changes in a storm's intensity. The society says: ``The inability to anticipate these changes for a storm that is less than 24 hours from landfall is of great concern.''

Weather science now is at a point where it can begin to overcome such limitations. Better computer forecasts using new powerful computers now are possible, and a new radar network already is being installed.

``The hurricane problem is complex and difficult, but it is not insurmountable,'' the society observes.