Hurricanes are tropical cyclones that typically occur in the warm waters of the Atlantic and Pacific oceans. When ocean waters heat up during the summer and fall, water evaporates into the lower atmosphere.
According to Wikipedia, hurricanes “…feed on heat released when moist air rises, resulting in condensation of water vapor contained in the moist air.” The released heat is called “heat of condensation”. The released heat is “distributed vertically around the center of the storm. Thus, at any given altitude (except close to the surface, where water temperature dictates air temperature) the environment inside the cyclone is warmer than its outer surroundings.”
In an ordinary thunderstorm, the released heat of condensation is carried away by surrounding strong winds (called “wind sheer”). But when the winds are calmer, the heat can continue to build in the vicinity; this heat build up creates an intense low-pressure system — leading to the formation of a hurricane.
Because of a phenomenon called coriolis force, hurricanes have counterclockwise rotation in the Northern Hemisphere and clockwise rotation in the Southern Hemisphere.
For more information on what causes hurricanes and how hurricanes form, visit the following Wikipedia reference: http://en.wikipedia.org/wiki/Tropical_cyclone
The animated hurricane image in this post is from the National Oceanic and Atmospheric Administration (NOAA)