Fast Facts on Hurricanes

Hurricane researchers have developed their own lingo for understanding these monster storms. The following information describes different types of storms, how they affect homes and communities, and how they are named.

The four basic categories of tropical weather events are tropical disturbance, tropical depression, tropical storm and hurricane.

A tropical disturbance is an organized tropical weather system that maintains its identity for more than 24 hours.

Tropical depressions have maximum sustained wind speeds of 38 mph or less -- stronger tropical storms have maximum sustained wind speeds from 39 to 73 mph.

When wind speeds reach 74 mph or more, the storm is upgraded to a hurricane.

Hurricanes are further categorized on a scale of increasing intensity known as the Saffir-Simpson Hurricane Scale, which ranks hurricane strength in Categories 1 to 5.

A Category 1 hurricane (winds from 74 to 95 mph) will mainly cause damage to trees and unanchored structures like mobile homes. Low-lying coastal roads can become flooded and some boats may be torn from moorings.

In a Category 2 hurricane (winds from 96 to 110 mph), some trees will be blown down. Mobile homes, roofs, piers and signs may sustain considerable damage, but no major damage to buildings will be experienced. Marinas and coastal roads will be flooded.

Hurricane Ivan, which struck coastal Alabama in 2004, was a Category 3 storm (winds from 111 to 130 mph). In these hurricanes, mobile homes and buildings near the coast can be destroyed by winds or battering waves. Serious flooding can block roads up to eight miles inland or more. Evacuation may be required near shorelines.

In a Category 4 hurricane, like August's Hurricane Katrina, wind speeds range from 131 to 155 mph. Large trees are blown down, beaches suffer major erosion, and roofs, windows and doors are often blown off structures. Escape routes can be cut by floodwaters three to five hours before the hurricane center arrives. Massive evacuations of residences within two miles of shore may be required.

The most extreme category of hurricane is Category 5, where winds exceed 156 mph. Hurricane Andrew, which destroyed large swaths of Miami and south Florida in 1992, was a Category 5 hurricane.

In a Category 5 storm, large trees, signs, residential and industrial buildings can be completely demolished. Some buildings are overturned or blown away. Glass is shattered in buildings over a wide area. The lower floors of buildings less than 15 feet above sea level sustain major damage from battering waves and debris. Because escape routes can be cut off by floodwater, massive evacuations of residences five to 10 miles from shore are often required.

The wind speeds noted here are for winds measured or estimated as the top speed sustained for one minute. Peak gusts, however, can be 10 percent to 25 percent stronger.

Hurricanes are given names to help speed communication among forecasters and the general public.

An Australian forecaster is credited with providing the first-known hurricane names -- he named storms after unpopular political figures.

In World War II, hurricanes were named after military meteorologists' girlfriends or wives. In 1979, men's names were included.

Storms from the Northwest Pacific basin have a different naming convention. The majority are names of flowers, animals, birds, trees or foods, and names are not allotted in alphabetical order, but are arranged by contributing nation.

Source: National Oceanographic and Atmospheric Adminstration, National Hurricane Center.

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