Killer hurricanes: are they becoming more frequent?

After three devastating hurricanes mauled the North American continent in the last five years, some experts have suggested this is the last five years, some experts have suggested this is the start of a cycle of killer storms. Jay Hobgood, assistant professor of geography, Ohio State University, argues that it's too soon to reach such conclusions, however. To find a true cyclical pattern - if it does exist - would take another 50 years worth of data, he says.

Hobgood indicates that he has found several clusters of major hurricane events in the last half-century, but that is a far cry from finding a true pattern of severe storms. He was looking for periods when the rate of major hurricanes exceeded the expected long-term average of one every three-and-a-half years.

Concern about a possible huricane pattern arose after Hurricane Andrew ravaged southern Florida in 1992. Before Andrew, Hurricane Hugo had devasted the Carolina coastline in 1989 and Hurricane Gilbert had assaulted the Caribbean the year before.

Three major storms in five years was way above average and some officials, including Robert Sheets, the director of the National Hurricane Center, wondered aloud if we were experiencing a repeat of the 1940s, when seven major storms struck Florida.

To try answer the question, Hobgood turned to the national Climate Data Center for available information on major hurricanes. Generally, hurricanes are ranked by the Saffir/Simpson Scale of Intensity, which classifies the storms based on maximum sustained wind speed and the...