In recent years satellite imagery has dramatically improved the ability of weather-watchers to detect hurricanes and to track their movements, thus extending the time that mariners and shore dwellers have to prepare for possible onslaughts. Technology for predicting landfalls also has improved. Anticipating the paths of these megastorms, however, is a famously inexact science. There are only probabilities, not guarantees.

The best tactic for coping with a hurricane is not to be there in the first place. But mass evacuations of coastal and low-lying inland areas pose their own dilemmas. Road capacity is limited in many heavily populated coastal and low-lying areas, creating the prospect of massive traffic jams. In 1999 residents of coastal Georgia driving north on I-95 to get away from Hurricane Floyd found themselves stuck behind northbound motorists in South Carolina who were stalled behind North Carolinians fleeing into Virginia.

Officials are reluctant to disrupt the lives of hundreds of thousands of people without assurance that they are in real danger; and because of the uncertainty of predictions, timely decisions may be hard to make.