NASA - National Aeronautics and Space Administration

The wind blows. The rain comes down. Hurricanes are powerful. They can rip a house apart. They can wipe out cities. But how do they start? And how do you know how big it will be? How can you tell how strong it is?

Image above: Hurricanes form in water. The orange parts show where they form. Credit: NASA

Let's figure it out.

Hurricanes start over the ocean. They need three things:

1. Warm water
2. Damp air
3. Winds that meet

When the wind blows at least 74 miles an hour, it is called a hurricane. That is very fast! It is faster than a car drives on a highway. Sometimes the winds blow faster than that.

Parts of a Hurricane

There are three main parts of a hurricane:

1. Eye -- This is the center. It is the calm part of the storm.
2. Eye Wall -- This part is around the eye. This part has the strongest winds and rains. The winds may blow 200 miles per hour.
3. Rain Bands -- These are the clouds that spin out and make the storm bigger.

Image above: There are three main parts of a hurricane. Credit: NASA

How Strong Is It?

Hurricanes can destroy what they hit. The winds can blow things down. The water can cover homes. The rains can cause floods. We can know how strong a hurricane is. There is a scale that is used to measure them. It is called the Saffir-Simpson Hurricane Scale. A hurricane can be on a scale of one to five. A level one does not destroy as much as a level five does.

CATEGORY	Click on each picture to see the movies.
One: There is not much damage.
Two: The winds blow at about 100 mph; it may break windows and destroy trees.
Three: It breaks windows and doors.
Four: There is much damage.
Five: This is the worst; winds blow at least 155 mph. It destroys buildings.

 
Adapted from Fierce Force of Nature: Hurricanes