Hurricanes can be unpredictable beasts with the power to deliver a blow ranging from relatively minimal to catastrophic to any landmass in its way. The damage is dependent upon several factors.

Not only is the intensity of the storm important, but geophysical factors such as the size of the storm and its associated windfield, surrounding synoptic weather situation, coastal geological features, and the astronomical tide situation play an important part.

The second major portion of this equation for disaster is the extent of economic, industrial, and residential development of the area affected. Following numerous on-site investigations of hurricane damage, especially that from Hurricane Camille, civil engineer Herbert Saffir devised a five-category damage scale in the early 1970’s.

The scale had the advantage of relating ranges of sustained winds to effects on vegetation and structures. Wind speed is the determining factor in the scale, as storm surge values are highly dependent on the slope of the continental shelf and the shape of the coastline, in the landfall region.

At the same time Robert Simpson, a former director of the National Hurricane Center, added additional reference to expected storm surge (the rise of a body of water above astronomical tide due to a tropical cyclone). And in 1972, the Tropical Prediction Center (then known as the National Hurricane Center) adopted the Saffir/Simpson Hurricane Scale to relate hurricane intensity and damage potential.

This scale uses the storm surge, central pressure, and/or the maximum sustained winds to classify Atlantic hurricanes into one of five categories.

In this way it is possible to give an estimate of the potential property damage and flooding expected along the coast from a hurricane landfall.

[bul]A Category One Hurricane has winds measuring between 74 to 95 mph and causes damage to unanchored mobile homes, shrubbery, trees and poorly constructed signs.

[bul]A Category Two Hurricane has winds measuring between 96 and 110 mph and causes the breaking of roofs, doors, windows, small trees are blown down and flooding two to four hours before the arrival of the hurricane centre.

[bul]A Category Three Hurricane has winds measuring between 110 to 130 mph and leads to the destruction of mobile homes, large trees are blown down and flooding takes place three to five hours before the arrival of the hurricane centre.

[bul]A Category Four Hurricane has winds measuring between 131 and 155 mph and causes curtain wall (building facade) failures in small residences, 10 foot flooding and necessitates evacuation as far inland as six miles.

[bul]A Category Five Hurricane has winds in excess of 155 mph and leads to complete roof failure, escape routes will be cut off by 15 foot flooding and necessitates evacuation as far inland as ten miles.

Had Katrina remained a Category Five storm, it would have been a rare event as only three other Category Five Hurricanes have torn through the US since record-keeping began: The Labour Day Hurricane of 1935, Hurricane Camille in 1969 and Hurricane Andrew in 1992.