The Most Powerful Storms

But even if Ivan's wind speeds at ground level drop 10 m.p.h., it will remain a Category 5 hurricane, which doesn't leave much in its path. Forget stop signs and light poles; facing 150 m.p.h. winds, small buildings will crumple.

The last two hurricanes to hit Florida - Charley and Frances - were Category 4 and 2 storms, respectively.

In 1969, an engineer named Herbert Saffir and Bob Simpson, then director of the National Hurricane Center, developed a wind-to-damage ratio chart.

A Category 1 storm, with winds of 74 to 95 m.p.h., uproots trees and damages mobile homes.

A Category 2 such as Frances, with winds of 96 to 110 m.p.h., causes door, roof and window damage.

A Category 3 hurricane, with winds of 111 to 130 m.p.h., can destroy mobile homes and wreck piers.

Category 4 storms will bring 131-to-155 m.p.h. winds to rip roofs off small houses and cause major beach erosion.

And once you get to a Category 5 storm, with winds above 155 m.p.h., Saffir and Simpson say, the damage is "catastrophic."