Hurricanes

Hurricanes

Hurricane Alex

Hurricane Alex, a category 3 storm at its strongest, traveled north along the east coast of North America in August 2004 causing flooding, strong waves, and rip tides along the coast.
Credit: NOAA

As a strong hurricane heads towards the coast, people prepare - boarding up houses, packing the car, and evacuating. These storms can spell disaster for people in hurricane prone areas. They are the most powerful of all weather systems. They are also huge storms – the average hurricane spreads across 340 miles.

Hurricanes form from disturbances in the atmosphere over warm, tropical ocean water. They die down when they move over land or out of the tropics and into cooler latitudes. These storms are called hurricanes in the Atlantic and typhoons or tropical cyclones in other areas of the world. Because of the Coriolis effect, the storms rotate counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. At the center of the rotating storm is a small area of calm weather and clear skies called the eye of the storm. Surrounding the calm of the eye are the most intense winds of the storm and thick clouds of the eyewall.

When a hurricane approaches land, strong waves and wind batter coastal towns. Hurricanes also cause a tremendous amount of rain in a short amount of time, which can cause rivers to flood their banks and flood areas that are both near the coast and further inland. But most coastal hurricane damage is typically flooding caused by storm surge – the temporary rise in sea level that happens as winds of the storm push water towards the coast. The low pressure of the storm also causes some storm surge. If storm surge happens at the same time as a high tide, the effect is more intense and more areas are flooded.

Not all storms are the same. Large and strong storms cause much more damage than small storms. In the Atlantic and Eastern Pacific, the Saffir-Simpson Hurricane Scale is used to describe the size of a hurricane.

As a hurricane moves across an ocean, scientists try to forecast where and when the storm will reach land. Their forecasts allow warnings to be issued in areas that the storm is likely to hit, giving people time to get out of the way. Watching hurricanes with weather satellites and using computer models to develop forecasts, scientists are able to predict the likely path of the storm. The models take into account what we know about the specific storm and what we know about the atmosphere. Since 1953 each hurricane has been given a name to help warn people that a new storm was on its way.

The window of the year when hurricanes are most likely is called hurricane season. This window of time is different in different regions of the world. In the North Atlantic, hurricane season is from June 1st to November 30th each year.

© 2011 NESTA with modifications by UCAR