Hurricanes Typhoons and Cyclones

What causes hurricanes?


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The term "hurricane" is just another word for a tropical cyclone which forms in the Atlantic Ocean or the eastern Pacific Ocean north of the equator.

Tropical cyclones (including typhoons and hurricanes) are caused by warm tropical moisture bearing clouds developing in open oceans or seas. Tropical cyclones such as hurricanes can only form over warm waters in the tropical regions of the oceans where the sea temperatures are 26.5 degrees Celsius (80 degrees Fahrenheit) or higher. They occur in areas of very low pressure when air that is heated by the sun rises rapidly, and becomes saturated with moisture which then condenses into high thunderclouds. As the atmosphere becomes favorable for development (no wind shearing in the higher parts of the atmosphere), normal thunderstorms clump together.

When the hot air rises, more warm air rushes in to fill the area left vacant by the hot air. The Coriolis effect of the Earth spinning on its axis causes the air to spiral inwards with considerable force. This in turn causes the winds to rotate faster, causing the tropical low to deepen in intensity into a tropical depression, and eventually a cyclone/ hurricane which is anywhere between hundreds of kilometres to thousands of kilometres wide.

Strong tropical cyclones such as hurricanes are also characterized by strong winds, yet in their center is a clear, calm region called the 'eye'. When the storm continues its course, and the winds return from the other direction, they may seem to be more violent. The winds are not just rotating; there is also the effect of the warmer air continually rising. Not only are the winds moving at high speed horizontally, but they are simultaneously moving at relatively high speeds vertically. That is why the winds are so strong, and seem to move in all directions.