What is a Hurricane?

A hurricane is a type of tropical cyclone.  Tropical cyclones have a collection of thunderstorms and clouds that spiral counterclockwise (in the Northern Hemisphere) around a center of low pressure.  These powerful forces of nature bring flooding rain, strong winds, damaging storm surge (ocean waters pushed onshore), and sometimes tornadoes.

Hurricane Isaac (2012) before making landfall in Louisiana. Image courtesy of NASA.

How do we classify hurricanes?

Hurricanes are classified by the Saffir-Simpson hurricane wind scale. The Saffir-Simpson hurricane wind scale classifies hurricanes based on their potential to cause damage. The scale goes from Category 1 to 5 based on maximum sustained wind speed (the average wind speed near the surface over a 1-minute period). Any hurricane classified as a Category 3 or above is considered a "major" hurricane.

Category Wind Speed Potential Damage
1 74-95 mph
119-153 km/h
Very dangerous winds will produce some damage.
2 96-110 mph
154-177 km/h
Extremely dangerous winds will cause extensive damage.
3 111-129 mph
178-208 km/h
Devastating damage will occur.
4 130-156 mph
209-251 km/h
Catastrophic damage will occur.
5 157 mph or higher
252 km/h or higher
Catastrophic damage will occur.

For weaker tropical cyclones, there are two additional classifications.

  • Tropical Storms have a wind speed of 39-73 mph (63-118 km/h). This is when a storm receives a name.

  • Tropical Depressions have a wind speed of less than 39 mph (63 km/h) and are the weakest tropical cyclones.
  • Where do hurricanes occur?

    All tropical cyclone tracks from 1985-2005.

    Hurricanes form in many different parts of the world, wherever the conditions are right, though sometimes they are known by a different name. In the Western North Pacific, they are called typhoons. In the Southern Hemisphere and Indian Ocean, they are called cyclones.

    For more information, please visit:

    National Hurricane Center – About Tropical Cyclones

    Hurricane Research Division - FAQ About Tropical Cyclones

    The Weather Channel – Hurricane Central

    About Cyclones in Australia