Hurricane Facts

Hurricanes usually start in the tropics as a low pressure system accompanied by powerful thunderstorms. A hurricane is a type of tropical cyclone, the general term for all circulating weather systems over tropical waters (counterclockwise in the Northern Hemisphere). Tropical cyclones are classified as follows:

Tropical Depression
An organized system of clouds and thunderstorms with a defined circulation and maximum sustained winds of 38 mph (33 knots) or less.

Tropical Storm
An organized system of strong thunderstorms with a defined circulation and maximum sustained winds of 39 to 73 mph (34-63 knots).

Hurricane
An intense tropical weather system with a well defined circulation and maximum sustained winds of 74 mph (64 knots) or higher.

In the western Pacific, hurricanes are called "typhoons," and similar storms in the Indian Ocean are called cyclones.

Hurricanes are products of a tropical ocean and atmosphere. Powered by heat from the sea, they are steered by the easterly trade winds and the temperate westerlies as well as by their own ferocious energy. Around their core, winds grow with great velocity, generating violent seas.

Moving ashore, hurricanes sweep the ocean inward while spawning tornadoes and producing torrential rains and floods. Each year, on average, 10 tropical storms, of which six become hurricanes, develop over the Atlantic Ocean, Caribbean Sea, or Gulf of Mexico. Many of these remain over the ocean; however, about five hurricanes strike the United States coastline every three years. Of these five, two will be major hurricanes, category 3 or greater on the Saffir-Simpson Hurricane Scale

Hurricanes can be as much as 200 miles wide and eight miles high with winds from 74 mph to more than 155 mph. The storm surge itself can be as high as 18 feet above the ocean's tide.

Hurricanes typically move at a forward speed of eight to 25 miles per hour. While this may seem quite slow, such movement can advance an approaching storm up to 200 miles during the course of a normal workday.

« this page last modified 05/11/06 »