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How Do Hurricanes Form?

2017-09-09

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[00:00.00]
  • Three powerful ocean storms threaten the Caribbean, the coast of the southeastern United States and southeastern Mexico.
  • [00:10.49]
  • Hurricane Irma has struck Cuba and now threatens the state of Florida with strong winds and rain.
  • [00:19.34]
  • The storm has caused deaths and widespread destruction on several Caribbean islands.
  • [00:27.34]
  • Hurricane Katia is in the southern Gulf of Mexico.
  • [00:31.85]
  • It is nearing Mexico’s eastern coast.
  • [00:35.68]
  • And Hurricane Jose is gaining strength in the Atlantic Ocean.
  • [00:41.43]
  • The three hurricanes come as the state of Texas recovers from Hurricane Harvey.
  • [00:47.94]
  • The huge storm caused severe flooding and billions of dollars in damage in Houston, the country’s fourth-largest city.
  • [00:58.83]
  • Hurricane season in the Atlantic Ocean goes from June 1 to November 30.
  • [01:06.06]
  • And the month of September is the peak of storm activity.
  • [01:11.50]
  • Hurricanes are the most powerful storms in the Earth’s atmosphere.
  • [01:18.05]
  • The storms have different names depending on where they take place.
  • [01:24.62]
  • Scientists call all these storms tropical cyclones.
  • [01:29.45]
  • If the storms form over the Atlantic Ocean or eastern Pacific Ocean, they are called hurricanes.
  • [01:38.69]
  • Storms that form in the western Pacific Ocean are known as typhoons.
  • [01:45.71]
  • In the Indian Ocean, they are called cyclones.
  • [01:50.31]
  • Although they have different names, all these storms form in the same way.
  • [01:57.92]
  • Scientists at the American space agency NASA describe tropical cyclones as huge weather “engines” that use warm, moist air as fuel.
  • [02:14.48]
  • They can only form over warm, tropical waters near the equator.
  • [02:21.25]
  • A tropical cyclone develops when warm moist air near the surface of the ocean rises.
  • [02:30.69]
  • This creates an area of unusually low air pressure.
  • [02:35.62]
  • Higher-pressure air from surrounding areas pushes in to take the place of the warm, rising air.
  • [02:44.80]
  • It becomes warmer and moister and rises, too.
  • [02:49.47]
  • The rising, moist air goes high into the atmosphere, where temperatures are low.
  • [02:57.32]
  • This creates wind. The moisture forms clouds.
  • [03:03.32]
  • The developing weather system begins to spin because of the Earth’s rotation.
  • [03:10.01]
  • As the storm spins faster and faster, what is called an “eye” of the storm develops at its center.
  • [03:19.85]
  • This is a calm area of very low pressure. Higher pressure air from above flows down into the eye.
  • [03:31.63]
  • When wind speeds reach about 63 kilometers per hour, meteorologists say a tropical storm has formed.
  • [03:42.89]
  • When winds in the storm are measured at 119 kilometers per hour or above, a tropical storm officially becomes a category one “tropical cyclone,” or in the Western Hemisphere, a hurricane.
  • [04:02.95]
  • Meteorologists use measurements of wind speed to place tropical cyclones in categories.
  • [04:12.17]
  • When a hurricane’s wind speed reaches 155 kilometers an hour, it is called category two.
  • [04:21.94]
  • The categories go up to category five, the most dangerous and catastrophic storm.
  • [04:31.04]
  • A category-five storm has wind speeds measured at over 250 kilometers per hour.
  • [04:40.55]
  • They can cause a storm surge, or a rise in water levels of more than five meters.
  • [04:49.93]
  • The National Oceanic and Atmospheric Administration, or NOAA, operates two satellites that track weather and storms in the eastern Pacific and Atlantic Oceans.
  • [05:05.44]
  • NOAA provides maps from the (GOES) satellites online.
  • [05:11.39]
  • I’m Mario Ritter.
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