01 October 2004

Hurricane season

Forrest M. Mims III

The 2004 hurricane season has disrupted the lives of millions of people. Several killer hurricanes have caused billions of dollars in property damage as they swept across the Caribbean and the southern United States.

The arrival of three major storms in quick succession is unusual but not unprecedented. What’s unusual is the reduced frequency of hurricanes in recent years.

From 1900 to 1996, 158 hurricanes struck the United States. Sixty-four of these storms were classified as major.

Florida was struck by 57 of these hurricanes, making it the number one hurricane target during this period. Twenty-four of these storms were major.

Texas was struck by 36 hurricanes during this period. Fifteen storms were classified as major. This is an average of around one hurricane every two and a half years.

This suggests that Texas is overdue for a hurricane.

Hurricanes begin life as clusters of thunderstorms over warm ocean water. Hurricanes that strike North and South America can originate in the Atlantic Ocean, Pacific Ocean or the Gulf of Mexico.

The largest and most powerful hurricanes usually originate off the west coast of Africa near the Cape Verde Islands. These storms may take up to two weeks to cross the Atlantic, which provides plenty of time for them to intensify.

Hurricanes are ranked in five intensity levels by the Saffir-Simpson Scale. A category one hurricane has winds of 74-95 mph that can damage Unanchored mobile homes and trees.

A category two hurricane has winds of 96 to 110 mph, and a category three storm has winds of 111 to 130 mph. These storms can cause severe damage to roofs, windows, doors and signs. They can destroy mobile homes and blow down trees.

Category four hurricanes have winds of from 131 to 155 mph and cause extensive damage to property and trees. Category five storms are rare events with winds greater than 156 mph that cause catastrophic devastation.

Hurricane Gilbert of 1988 was a record category five hurricane. Gilbert killed 318 people on its track of destruction across Yucatan, Mexico and Texas.

Now Ivan has joined the record books as one of the most powerful hurricanes ever observed.

Forrest M. Mims III and his science are featured online at http://www.forrestmims.org/.

This feature was originally published in Forrest Mims's weekly science column in the Seguin Gazette-Enterprise, Seguin, Texas. The column is written for a general audience.