hurricanes

Hurricanes are tropical storms with winds over 74 miles per hour and lots of rainfall. They start over warm, tropical oceans. Hurricanes get their heat and energy from the warm ocean waters. As the water evaporates, the hurricane gets stronger. They can last longer, and sometimes move much further, over water than over land. The combination of heat and moisture, along with the right wind conditions, can create a new hurricane.

When a hurricane hits land, it tends to weaken because it has lost its source of energy, the warm ocean waters.

Hurricanes are known as ‘typhoons’ in the western Pacific, ‘cyclones’ in the Indian Ocean, and ‘baguios’ in the Philippines.

Each storm usually lasts for an average of nine days. The ocean water temperature has to be above 79 degrees in order for a hurricane to be formed, so they normally appear in late summer and early fall when the conditions are right.

Hurricanes have two main parts. The first is the eye of the hurricane, which is a calm area in the center of the storm. Usually, the eye of a hurricane measures about 20 miles in diameter, and has very few clouds. The second part is the wall of clouds that surrounds the calm eye, called the eyewall. The eyewall is the area inside the hurricane where the winds and rain are the worst. Winds can be up to 186 mph!

When the eye of a hurricane passes over a region, the winds decrease to just a gentle breeze, and the rain stops. You may even be able to see the sun during the day or the stars at night. Then the rest of the storm passes and the wind suddenly changes directions and becomes strong again. In the northern hemisphere hurricanes usually rotate counter-clockwise.

Hurricanes can be very dangerous. The strong winds and heavy rains can raise sea levels and cause flooding. Hurricanes can create tornadoes. Often the right side of a hurricane causes the worst damage.

Meteorologists give hurricanes names, which are reused unless the storm is particularly destructive. The names used to be all women's names, but since 1979, men's names have been used, too. Six lists are used in rotation. Thus, the 2004 list will be used again in 2010.

Is your name going to be used for a hurricane? Check here! A name is retired if that hurricane caused a lot of damage or many deaths.

There are three types of damage caused by hurricanes:

Wind Damage: Hurricane-force winds, 74 mph or more, can destroy poorly constructed buildings and mobile homes. Debris, such as signs, roofing material, siding, and small items left outside, become flying missiles in hurricanes. Winds can often stay strong well over land.
Storm Surge Damage: Heavy ocean waves caused by a hurricane is a storm surge. They are very dangerous, and a major reason why you must stay away from the ocean during a hurricane warning or hurricane. It can often be 50 to 100 miles wide. It sweeps across the coastline near where a hurricane makes landfall. The surge of high water topped by waves is devastating. The stronger the hurricane and the shallower the offshore water, the higher the surge will be. Along the immediate coast, storm surge is the greatest threat to life and property.
Flood Damage: Widespread torrential rains often in excess of 6 inches can produce deadly and destructive floods. This is the major threat to areas well inland.

Storm Surge

Photo from NOAA

In less than a 4 week period in 1992, two major hurricanes hit the United States leaving an unprecedented amount of destruction. First Hurricane Andrew pounded Florida and Louisiana to become the most expensive natural disaster in U.S. history, with damage estimates in the range of $15 billion to $30 billion. Then 3 weeks later, Hurricane Iniki affected three Hawaiian islands resulting in over $1 billion in damage, particularly in Kauai.

Hurricanes and their potential for destruction are rated using a scale from 1 to 5 called the Saffir-Simpson Scale. A Category 1 hurricane is the least dangerous and a Category 5 hurricane is the most dangerous.

Saffir-Simpson Hurricane Scale

Category	Damage	Wind Speed	Storm Surge
1	Minimal	74-95 mph	4-5 feet
2	Moderate	96-110 mph	6-8 feet
3	Extensive	111-130 mph	9-12 feet
4	Extreme	131-155 mph	13-18 feet
5	Catastrophic	155+ mph	18+ feet