What Is a Hurricane?

[wind blowing] Hurricanes need very specific ingredients to form, and the most important ingredient is warm ocean water.

[waves crashing] Hurricanes usually start over tropical oceans, where the water is at least about 80 degrees Fahrenheit.

The warmer the water, the faster the water molecules are bouncing.

[molecules bouncing] And you know another word for fast, bouncing molecules? We call it energy.

[lightning striking] [upbeat music] The warm water is full of energy, and guess what loves energy? Hurricanes.

[lightning striking] So it usually begins with a group of thunderstorms forming over the ocean.

[thunder clapping] Warm air near the surface of the water starts to rise, because warm air is lighter than cool air, and as that warm, moist air rises, it leaves behind an area of low air pressure near the ocean surface.

So nearby air rushes in to fill that space, but then that air warms up, and it rises, too, which creates more low air pressure near the ocean, so then [laughs] more air pulls in, and that air warms up, and then it starts to rise, so then more air comes in, and it warms up and starts to rise.

Y- you see how, you see how this thing gets started? [upbeat music] As the air rises higher into the sky, it cools down and forms clouds and rain.

[rain falling] When this happens, heat is released into the storm.

That extra heat gives the storm even more energy, helping it grow stronger.

The more warm water the storm sits over, the more energy it can steal from the ocean.

Here's where things get really interesting: because the Earth is spinning, moving air doesn't travel in straight lines.

Instead, it starts to curve.

This makes the storm begin to spin, [thunder clapping] forming a giant swirling system.

That spinning motion helps organize the storm and pull in even more air and moisture.

Do you see how everything that is happening is creating more power, more spinning, more, more, more? [lightning striking] [upbeat music] Well, except for one spot.

[gentle music] See, as the storm grows stronger, it can form a calm center, called the eye.

The eye is quiet, with lighter winds, and sometimes even clear skies.

Around the eye is the eye wall.

[lightning striking]Which is the most dangerous part of the hurricane.

That's where the strongest winds and the heaviest rains are found.

Further out are bands of rain and storms that spiral around the center.

Now, a storm officially becomes a hurricane when its winds reach 74 miles per hour or faster.

That's about as fast as your car drives when it's on the interstate.