Bracing for Disaster

23 January 2012

Where do hurricanes come from and how are they formed? Read on to learn more about these swirling storms...

A hurricane is one name for a tropical cyclone. In order to be called a hurricane, it must occur within the North Atlantic Ocean, the Northeast Pacific Ocean (east of the dateline) or the South Pacific Ocean east of 160E. Tropical cyclones in other areas of the world are known as typhoons or cyclones.

Did You Know?
Hurricanes are typically about 480 km wide and travel at speeds of 24-32 km/hr. A hurricane begins to form when warm moist air rapidly evaporates from the ocean's surface up into the atmosphere. The ocean must be at least 26.5ºC for this to occur on hurricane scale. As the moist air rises it cools and condenses to form large storm clouds. The cooling water also causes a large amount of heat to be released into the air. The heat released by the cooling water powers large winds that start to absorb the extra heat in this new weather system.

At the same time, winds near the ocean surface converge at the bottom of the storm and help to push even more warm air upwards. The storm begins to feed itself, sucking up more and more warm, moist air as new wind currents sweep in towards it. All this rapidly moving air creates an area of low pressure at the centre of the hurricane, known as they eye of the storm. This area is usually very calm, but the walls of the eye contain the most violent winds.

Did You Know?
The amount of heat energy released by an average hurricane is equivalent to the amount of electric energy produced by the U.S. in an entire year (American Red Cross 2001). The circular twisting motion of a hurricane is caused by the Coriolis Effect. The rotation of the Earth causes tropical cyclones to rotate counterclockwise in the Northern hemisphere and clockwise in the Southern hemisphere. Because tropical cyclones can only be called hurricanes if they occur in the Northern hemisphere, all hurricanes spin counterclockwise.

A tropical cyclone will first become a tropical depression and then grow into a tropical storm. If the storm occurs within the correct region and reaches sustained wind speed of over 118 km/hr, it becomes a hurricane.

There are five classes of hurricanes, which are designated using the Saffir-Simpson Scale. Since the power of a hurricane comes from the warm, moist waters beneath it, these storms tend to degenerate quickly once they reach land. However, they often cause plenty of damage before they completely die out.

For more detailed information about the Saffir-Simpson hurricane designations visit The National Hurricane Centre website listed below.

Did You Know?
The most powerful hurricane ever recorded over the Atlantic was Hurricane Wilma in 2005, with sustained wind speeds of over 280 km/hr When a tropical cyclone reaches the stage of tropical storm it receives a name. The names come from one of several pre-selected lists. The names alternate between masculine and feminine. If a storm or hurricane causes significant damage, any country affected by the storm can request to have the hurricane name retired, just like retiring jersey numbers in sports.

Hurricanes can cause millions and even billions of dollars in damage to cities and other places of human residence. Destruction of property through wind damage and flooding can be extensive.

The stagnant and contaminated water left behind by hurricanes can lead to increased spread of disease. Natural environments can also be affected by hurricanes. Coral reefs are one example of a habitat that can be damaged by the storm surges that generally accompany hurricanes.

There are however some benefits of these massive storms. They can bring welcome relief to areas suffering from drought. They also move large masses of very warm air northward and out of tropical regions, helping to moderate temperature in the areas they form.

Hurricanes are fascinating weather systems. Many scientists are currently working to better understand their formation and predict their path. If you are interested in learning more about hurricanes visit any one of the following websites:

The National Hurricanes Centre (USA)

The American Red Cross

How Stuff Works

National Oceanic and Atmospheric Administration

Robyn Auld is a doctoral student at Memorial University of Newfoundland, where she is studying Entomology (the study of insects). She has a degree in Environmental Science from the University of Ottawa. Outside of studying bugs, Robyn loves playing Ultimate Frisbee!


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