How Hurricanes Form

Hurricanes are huge!

They can be up to 600 miles across and have strong winds spiraling inward and upward at speeds of 75 to 200 miles per hour. Hurricanes last for over a week, and they move over time. They move fastest over the open ocean (as fast as 20 miles per hour). With warm air at their centers, hurricanes are different from storms that happen in the middle latitudes like the United States.

The center of a hurricane is the calmest part. It is called the eye and has only light winds and fair weather. Wind of a hurricane blow counterclockwise around the eye at the Earth's surface in the northern hemisphere (clockwise in the southern hemisphere).

There are five things that a hurricane needs.

  1. Hurricanes take energy from the warm ocean water to become stronger. While a hurricane is over warm water it will continue to grow.
  2. Winds flow towards the center of the storm low in the atmosphere and air is forced upward.
  3. High in the atmosphere the winds flow away from the storm, which allows more air from below to rise.
  4. The air that rises needs to be warm and moist so that it forms the clouds of the storm. Warm, moist air is found above warm, tropical ocean waters.
  5. A hurricane also needs the winds outside the storm to be light. These winds steer the storm, but are not strong enough to disrupt it.

 

A hurricane dies when it moves away from the tropics. When a hurricane moves into areas with cooler ocean water, it weakens. It will also weaken if it travels over land.

© 2013 UCAR