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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 low central air pressure within them. The scale goes from category one (the weakest type of storm, labeled "minimal") to category five (the strongest type, considered "catastrophic"). Hurricane Gilbert was a category five storm, while Hugo and Andrew were both classified as category four.

Hobgood found that only 25 out of 904 storms in the last 107 years reached the category-four of -five intensity, based on known wind speeds. When he factored in the low atmospheric pressures within them, he added another seven, bringing the total of severe storms to 32. That's how he reached his "one severe storm every three-and-a-half years" rate.

"Clearly, if you look at the most intense storms, having three over the last five years would exceed the long-term average. However, it isn't unprecedented. There have been periods in the past when we had similar clusters of years in which there have been category-four hurricanes."

Hobgood pointed to a period between 1964 and 1967 when there were three category-four or -five storms during the 1960s, and the period between 1955 and 1958 saw three in category four. "Clearly, in the past, we have seen times when intense hurricanes have been as frequent as we have seen them in the last five years."
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Publication:USA Today (Magazine)
Date:Jun 1, 1993
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