Hurricanes are a type of tropical cyclone. Tropical cyclones are massive tropical storms with extremely strong winds that spiral around a center of low air pressure. These storms form over warm ocean waters around the world. Because warm water fuels them, they typically form in tropical waters within 5 to 25 degrees latitude north or south of the equator. Prevailing winds can then steer them to latitudes farther north or south of the equator. Tropical cyclones are variously named in different parts of the world. Those that form in the western Pacific Ocean are called typhoons. Those that form in the Indian Ocean and the South Pacific Ocean are called cyclones. Those that form in the Atlantic Ocean and eastern Pacific are called hurricanes.

 

In the Northern Hemisphere tropical cyclones spiral counterclockwise, whereas in the Southern Hemisphere they spiral in a clockwise direction. The spiraling of the winds is produced by Earth’s rotation. The phenomenon is known as the Coriolis Effect. Generally, the farther from the equator a storm is positioned, the more this phenomenon affects the storm.

 

A hurricane typically has a circular shape and an average diameter of about 480 km (300 mi). The storms are made up of many bands of thunderstorms that spiral outward in a counterclockwise direction from a central “eye.”

 

The eye of the hurricane is a circular region with few clouds and very light winds at the center of the storm. This is the calmest part of the storm. Not every hurricane has an eye; but, if one develops, its diameter usually ranges from about 8 km (5 mi) to over 200 km (120 mi). A hurricane’s eye has the lowest surface air pressure in the storm. Scientists measure the air pressure in the eye to understand and forecast how strong the storm will be. Air in the center of the eye slowly sinks from above, becoming warmer and drier as it sinks. For this reason, a hurricane’s eye has few clouds.

 

The region surrounding a hurricane’s eye is called the eyewall. The eyewall is a wall of clouds and is usually considered the most deadly part of the hurricane. Moist air rises through the spiraling winds of the eyewall, releasing heat as an energy source for the hurricane. As the air rises, water vapor condenses and tall thunderstorms form. Heavy rain and extreme wind characterize the eyewall.

 

Many rainbands exist beyond the eyewall. Rainbands are regions of heavy thunderstorms that spiral outward from the center of the hurricane. The strongest rainbands usually occur 90 degrees clockwise to the track of the storm. The thunderstorms form where moist air rises. Areas of lighter precipitation separate the rainbands. In these areas, air does not rise as much or may even sink.

 

Tropical cyclones, which include hurricanes, typhoons, and cyclones, have a complex structure of clouds, rain, and winds.