Dictionary Definition

A severe tropical cyclone involving heavy rains and originating in the equatorial regions of the Atlantic Ocean or the Caribbean Sea.

Anatomy

All hurricanes are built with a basic structure. Below is a description of the parts, working from the center outward.

• Eye: The small hole at the center of the hurricane. This part is the calmest part of the hurricane, and has the least amount of pressure. However, some winds and light rain can occur in this area. When the eye comes over the land, it brings a blue sky or scattered clouds, making it look like the storm is over. However, the eye moves on and the second half follows with winds blowing from the opposite direction.
• Eye Wall: A bright ring of clouds directly outside of the eye, which has the heaviest activity of the hurricane.
• Squall Bands: A series of bands that makes up the hurricane. Each area has violently gusting winds, heavy rain, and thunderstorm activity. The clouds of each squall band merge across the top, so the hurricane appears as an unbroken swirl of clouds when viewed from a satellite. The winds within the squall bands grow stronger the closer they are to the eye, so that is why the eye wall is the strongest.
• Feeder Bands: These bands extend from outside the hurricane into the outer edges of the storm to feed energy into the storm.
• Tail: The end of the storm where the winds spiral outward.

Formation

Hurricanes develop in tropical oceans on both sides of the equator, and are born as tropical depressions where the surface temperature of the sea is at least eighty degrees Fahrenheit. They must be fairly close to the equator for the heat, but they can't get too close or else they won't build the necessary spin. Tropical cyclones are more common in summer and autumn, when the sun can heat the sea well to the north or south of the equator. A hurricane uses the heat energy from the warm water to power itself. The eye of the hurricane draws in warm air, which rises, cools, and spreads out to make the storm grow. The path of the wind on the way up the eye is a spiral, due to the rotation of the earth's surface. In the Northern Hemisphere, the winds spiral counterclockwise, and in the Southern Hemisphere they travel clockwise. Only one out of ten tropical depressions grow into full-blown tropical cyclones, and they last from a couple days to as long as four or five weeks. The formed hurricanes normally head westward, guided by the trade winds; therefore the countries in the western portions of the oceans are at the greatest risk. If a hurricane curves away from the equator, and enters the cold water, it will die from being deprived of its energy source. A typical hurricane is 300 to 400 miles in diameter, with the winds circling at over seventy-five miles per hour. The eye ranges from five to twenty-five miles in diameter. The largest eye ever measured was the forty-by-eighty-mile elliptical eye of 1955's Hurricane Diane, which was centered over Chesapeake Bay. The average forward speed of a hurricane is about fifteen miles per hour, but can get to forty miles per hour when the storm reaches higher latitudes.

Dangers

Hurricanes can be very dangerous, especially when wind speeds exceed 100 miles (160 kilometers) per hour. Winds like that can snap and uproot trees, hurl debris through the air, rip roofs from sturdy buildings, flatten flimsy structures, and more. To escape from the wrath of the hurricane, people must seek shelter in strong building with boarded windows. After the hurricane comes through, the flooding that follows can be just as devastating. High water levels will rise onto the coast and devastate the homes, especially if water is blown shoreward along a gradually sloping or flat coastline. The rainfall that accompanies hurricanes makes the flooding even worse, and can produce flash flooding, urban flooding, and major river flooding. Another hazard that hurricanes bring is the tornadoes that frequently develop in the hurricane, which develop 50 to 150 miles from the eye of the hurricane.

Erratic Behavior

Hurricanes often change their course throughout their lifespan, and Hurricane Elena is a good example. On August 22, 1985, Elena was born off the western coast of Africa. The next week she moved rapidly westward across the Atlantic at thirty miles per hour with circular winds of about twenty-five miles per hour. When she reached Cuba on August 27, she was classified as a tropical storm as she sustained circular winds of about fifty miles per hour. Two days later, with circular winds at seventy-five miles per hour, Hurricane Elena was considered a hurricane. She then moved through the Gulf of Mexico toward New Orleans. Then suddenly she veered eastward toward Florida, and then changed course once again for the coast of Mississippi. She finally struck the Gulfport-Biloxi are on September 2, with winds at 130 miles per hour. During her indecisive five days, nearly half of the Gulf coastline was put under hurricane warning at one time or another, and 1.5 million people were evacuated. Causing half a billion dollars worth of property damages, Hurricane Elena was the forth costliest hurricane on record.

Forecasting

The fast hurricanes, that move at least 12 miles (19 kilometers) per hour, are the easiest to predict because they storms usually stay on the same course, without any drastic change. The slow moving hurricanes often change course dramatically throughout their run, making it harder to predict which way they will go. Observing the upper-level winds over the ocean is helpful in predicting the movement of the hurricanes, but the data is hard to get unless there is an island to place a station at. Therefore, forecasting relies more on computer models and analysis of past hurricane patterns. Satellites are also very helpful for forecasting hurricanes because they constantly survey the seas and coasts, warning forecasters of a hurricane before it gets to the coast.

Naming

Hurricanes are given names to make it easier to refer to several storms occurring at the same time. Also, it is easier to remember significant past storms by name than by the exact dates of the storm. When it reaches tropical-storm status, the storm is given a name. Meteorologists began giving names to individual hurricanes and tropical storms in the 1940s. In the beginning, the storms were named using old military designators, such as Able, Baker, Charlie, Dog, Easy, and Fox. So,each year had its own Hurricane Abel, Hurricane Baker, and on through the alphabet. Then in 1947, a list of alphabetized female names was compiled. Today the hurricane names are alternating male and female names, and are also alphabetized. One set of names is used for the storms east of North America, another for those west of North America, and a third for those in the western North Pacific Ocean. If a storm is particularly violent, it may be taken off the list. Camille, whichswept the Mississippi Delta in 1969 is no longer used. Neither is Hugo, which battered the Islands, Puerto Rico, and Charleston, South Carolina, in 1989. Andrew of 1992, Diana of 1990, and Gilbert of 1998 are some other hurricanes that were retired.

World

Hurricanes have many names, depending on where you are in the world.