How Do Hurricanes Form?

Sep 15, 2017

In the last couple of weeks, two big hurricanes have hit parts of the United States and Caribbean islands. In this episode we answer questions from kids who have been hearing the news and wondering: How do hurricanes form? Why do hurricanes strike Florida? Why do hurricanes have names? We speak with atmospheric scientist Shuyi Chen of the University of Washington.

Chen isn't the person you'd see on TV giving a weather forecast. She's one of the scientists who develop the computer models that predict where a storm might hit and what path it's likely to take.
 

"How do hurricanes form?" Auden, 7, New Hampshire and Charlotte, 6, Florida.

"Hurricanes form over the ocean when you have very warm water. Hurricanes take that warm water energy, that water vapor, into the atmosphere," Chen says.

But water vapor rises into the clouds every day, so why isn't there a hurricane every day? That's because there are other conditions a hurricane needs as well. It needs winds that are blowing more gently high up in the atmosphere and stronger near the earth's surface.

"You can think of a hurricane as a big cylinder. Like a big water bucket, it needs to stand up straight," Chen explains. "If the winds start to blow hard on top, they tilt and the hurricane doesn't like that. So we have warm water, we have wind that blows relatively vertically straight, and we also need a lot of water vapor in the atmosphere to form clouds."

Water vapor accumulates in the clouds and, under normal circumstances, that could cause a thunderstorm. But a hurricane is different because it needs winds that are blowing almost straight up the side of that hypothetical bucket. Then something has to kick it off to get it swirling.

"Far away in the Africa coast, we have the wind blow in a swirly way, we call a disturbance," Chen explains. "That starts the thunderstorm and the thunderstorms start to collect together and they'll move over the warm water in the Atlantic Ocean and then we have the wind that is really favorable for them to form, so when all these good conditions get together then the hurricane can form."

The end of summer is a time when all of those conditions come together to create hurricanes.

Listen to the full episode for answers to why hurricanes strike certain parts of the United States, what hurricanes in the Pacific are called and to learn about the naming system for hurricanes.

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If you want to help out the victims of hurricanes Harvey and Irma, NPR has complied some helpful lists of where to give.

Hurricane Harvey

Hurricane Irma

Auden, left, lives in New Hampshire; Charlotte, center, 7, lives in Florida; and Jordyn, right, 6, lives in New York.
Credit Courtesy of parents

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