Hurricanes, also known as tropical cyclones, form over warm, oceanic water. Without the aid of warm winds and water, they could not exist. When warm air rises from the ocean's surface, an area of low pressure is built below.
Hot air rises and cold air sinks, as we know. In equatorial regions, or places close to the Earth's equator, the oceans are warm so the air that is above the water is also a warm temperature. As warm air rises, it leaves less air at the ocean's surface. This causes an area of low pressure. An area of low pressure is like a vacuum, drawing high air pressure to it. When the high pressure moves in, more air is available to rise up. As the warm air rises, the atmosphere cools it off, creating moisture. The moisture becomes clouds.
As more clouds form and more warm air is pushed upwards, the clouds combine and begin spinning. The water beneath the clouds spins, too. Hence the name "tropical cyclone," as the spinning mirrors tornadic activity on land. In the Northern Hemisphere, hurricanes rotate counterclockwise, and in the Southern Hemisphere, they spin clockwise.
The continuous influx of warm air feeds the hurricane. Spinning increases and rotation of the entire system goes faster and faster, making the storm even more powerful. As the hurricane gathers strength, it develops what is called an eye. The eye is the center of the hurricane and is unlike the rest of the storm. Hurricane eyes are calm vacuums that draw high air pressure inside. If a hurricane 's eye were to pass over, you would find a clear sky with no wind. In past times as the eye crossed over, people thought the storm was finished. As the next part of the storm came, however, it was clear there was much more to come. The second part of a hurricane is even more violent and destructive, with winds blowing from the other direction.
Hurricanes have different ratings according to their wind speeds. For example, a category 3 hurricane has wind speeds of 111 to 130 mph, while a category 1 hurricane's winds are 74 to 95 mph. A category 5 hurricane is the worst kind, with wind speeds of over 155 mph. The National Oceanic and Atmospheric Administration (NOAA) has worked with NASA to place satellites above the earth to watch for storm formation. These satellites also track a hurricane's progress. Monitoring is the best way to warn people of the impending danger of a hurricane.
These magnificent and deadly storms contain strong winds, heavy rain, thunder, lightning and tornadoes. As hurricanes reach land, tides swell and a storm surge is created. Once on land, a hurricane loses its power and magnitude as there is no more warm air and water to feed it. It will drift over land, dumping large amounts of rain, but poses less and less of a problem.