Hurricane Growth Cycle

Hurricanes don't start off as full-blown monsters. They typically follow a growth cycle.

Tropical Disturbance
A tropical disturbance is the beginning stage, and is a moving area of thunderstorms that maintains its identity for 24 hours or more.

Tropical Depression
A tropical disturbance grows into a tropical depression. This is an organized system of clouds and thunderstorms with a defined circulation and maximum sustained winds of 38 miles per hour or less.

Tropical Storm
A tropical storm is formed when a tropical depression grows into an organized system of strong thunderstorms with a defined circulation and maximum sustained winds of 39 to 73 miles per hour.

A hurricane is formed when the storm reaches its full potential. Hurricanes are giant whirlwinds in which air moves in a large tightening spiral around a center of extreme low pressure., reaching maximum velocity in a circular band extending 20 or 30 miles from the rim of the eye. Winds will reach 74 miles per hour or more and blow around the eye, which is a relatively calm center. Near the center, winds may gust to more than 200 miles per hour. The entire storm dominates the ocean surface and lower atmosphere over tens of thousands of square miles.

The Eye
The eye is unique to hurricanes. Winds will be light and skies clear or partly cloudy. The calm is very deceptive, as it is bordered by maximum force winds and torrential rains. Many people have been injured or killed after being lured out of shelter by the calm of the eye, only to be caught in maximum winds at the far side of the eye where winds blow from a direction opposite to that in the leading half of the hurricane.