A hurricane is a type of storm called a tropical cyclone, which forms over tropical or subtropical waters.

image of Hurricane Sandy

Hurricane Sandy as seen from NOAA's GOES-13 satellite on October 28, 2012. NOAA's National Ocean Service helps coastal communities prepare for and recover from major coastal storms such as hurricanes.

A tropical cyclone is a rotating low-pressure weather system that has organized thunderstorms but no fronts (a boundary separating two air masses of different densities). Tropical cyclones with maximum sustained surface winds of less than 39 miles per hour (mph) are called tropical depressions. Those with maximum sustained winds of 39 mph or higher are called tropical storms.

When a storm's maximum sustained winds reach 74 mph, it is called a hurricane. The Saffir-Simpson Hurricane Wind Scale is a 1 to 5 rating, or category, based on a hurricane's maximum sustained winds. The higher the category, the greater the hurricane's potential for property damage.

Hurricanes originate in the Atlantic basin, which includes the Atlantic Ocean, Caribbean Sea, and Gulf of Mexico, the eastern North Pacific Ocean, and, less frequently, the central North Pacific Ocean. A six-year rotating list of names, updated and maintained by the World Meteorological Organization, is used to identify these storms.

"Hurricane Season" begins on June 1 and ends on November 30, although hurricanes can, and have, occurred outside of this time frame. NOAA's National Hurricane Center predicts and tracks these massive storm systems, which occur, on average, 12 times a year in the Atlantic basin.

As a world leader in hurricane research, NOAA strives to understand the mechanics of these complex storms in order to protect people, property, commerce, and natural resources.

For more information:
What is the difference between a hurricane watch and a warning?
Why do we name tropical storms?
What's the difference between a hurricane, a cyclone, and a typhoon?
National Hurricane Center