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Three powerful ocean storms hit the Caribbean, the coast of the southeastern United States and southeastern Mexico. They come as the state of Texas recovers from Hurricane Harvey (飓风哈维). The huge storm caused serious flooding and billions of dollars in damage in Houston, the country's fourth-largest city.
Hurricane season in the Atlantic Ocean goes from June 1 to November 30. And most storm activities happen in me month of September.
Hurricanes are the most powerful storms in the Earth's atmosphere. The storms have different names depending on where they take place. Scientists call all these storm tropical cyclones (热带气旋).
If the storms form over the Atlantic Ocean or eastern Pacific Ocean, they are called hurricanes. Storms that form in the western Pacific Ocean are known as typhoons. In the Indian Ocean, they are called cyclones. Although they have different names, all these storms form in the same way.
Scientists at the American space agency NASA describe tropical cyclones as huge weather "engines" that use warm, moist (潮湿的) air as fuel.
Theycan only form over warm, tropical waters near the equator (赤道).
A tropical cyclone develops when warm moist air near the surface of me ocean rises. This creates an area of unusually low air pressure.
Higher-pressure air from surrounding areas pushes in to take the place of the warm, rising air. It becomes warmer and moister and rises, too.
The rising, moist air goes high into the atmosphere, where temperatures are low. This creates wind. The moisture forms clouds. The developing weather system begins to spin because of the Earth's rotation (旋转).
As the storm spins faster and faster, an "eye" of the storm develops at its centre. This is a calm area of very low pressure. Higher pressure air from above flows down into the eye.
