Intro to Meterology: What Is a Hurricane?

A hurricane is an intense, rotating oceanic weather system that possesses maximum sustained winds exceeding 74 mph. In North America, we call this storm a hurricane. In other parts of the world, a hurricane is known by other names. In the Western North Pacific they are known as a typhoon and in the Indian Ocean and the Western South Pacific as a tropical cyclone. It forms over tropical oceanic regions. Hurricanes are generally smaller storms in mid-latitudes, typically about 500 km in diameter. In the Northern Hemisphere, the air spins inward and in a counterclockwise direction. Hurricanes depend on six conditions to form.

1. A pre-existing disturbance providing some initial spin and flow into the system.

2. Warm ocean temperatures (at least 80 degrees Fahrenheit) to a depth of about 150 ft.

3. Relatively light winds that do not change much in direction and speed up through the atmosphere.

4. A location at least 300 miles from the equator. Tropical cyclones require some of the spin provided by the Coriolis Effect.

5. An atmosphere that cools enough with height to allow thunderstorms to develop.

6. An atmosphere that is moist enough to fuel the thunderstorm.

Tropical cyclones are classified into four types, based on their wind speeds. These are the terms commonly used by forecasters:

· Tropical Depression: Maximum sustained winds of 38 mph or 33 knots

· Tropical Storm: Maximum sustained winds of 39-73 mph (34-63 kt)

· Hurricane: Maximum sustained winds of 74 mph (64 kt) higher

· Major Hurricane: Maximum sustained winds of 111 mph (96 kt) or higher

Hurricanes are categorized according to the strength of their winds using the Saffir-Simpson Hurricane Wind Scale. A Category 1 storm has the lowest winds speeds, while a Category 5 hurricane has the strongest.

· Category 1: Winds of 74-95 mph; Very dangerous winds will produce some damage

· Category 2: Winds of 96-110 mph; Extremely dangerous winds will cause extensive damage

· Category 3: Winds of 111-130 mph; Devastating damage will occur

· Category 4: Winds of 131-155 mph; Catastrophic damage will occur

· Category 5: Winds of 155+ mph; Catastrophic damage will occur