What Is A Hurricane?


A hurricane is a tropical storm that has winds of 74 miles per hour or more. The winds can sometimes reach up to 155 miles per hour. Another characteristic of hurricanes is their massive size that measures from 200 to 300 miles in diameter. In the center of each storm there is what is called the eye of the storm (Image to Right). The eye of the storm is usaually between 20-30 miles and is the calmest part of the storm. Winds here may only be 74 miles per hour. Some hurricanes can last for two weeks or more over open water and can run a path across the entire Eastern Seaboard.
A picture of the eye of the hurricane.
Hurricanes that develop in the Northern Hemisphere rotate in a counterclockwise motion and in the Southern Hemisphere they rotate in a clockwise motion. The direction of rotation all has to do with the rotation of the earth. Hurricanes only develop in the Atlantic Ocean, Gulf of Mexico, Indian Ocean, Caribbean Sea, and the Pacific Ocean. The major factors that effect the development of a storm, in the Atlantic Ocean, are ocean temperature, atmospheric pressure, the Gulf Stream, and wind currents. The first stage in storm development begins in a long, narrow region of low pressure that occurs in ocean winds. These areas are called the trade winds. This area of low pressure eventually grows into a tropical depression . Winds there can reach up to 31 miles per hour. The next stage in hurricane development is when the tropical depression grows into a full fledged tropical storm with winds up to 74 miles per hour. The last stage is when it finally becomes a hurricane. There is also a specific season, called Hurricane Season, when hurricanes are most likely to develop, between June 1 and Novenber 30. About 6 hurricanes each year occur during the hurricane season. Some hurricanes can even develop in the winter time, but that rarely happens, only three have been recorded since 1886.

Hurricanes are not only very violent storms but they are also very dangerous. The primary dangers of the storm are the rain/flooding, high winds, the occasional tornado, flying debris from buildings and nature (i.e. trees), and the storm surges . Storm surges can be between 50 to 100 miles high. These surges may be even more dangerous than any of the other hazards because they can wipe out an entire community near the ocean. Nine out of ten deaths are caused by such surges and annually 17 people die from hurricanes in the United States alone. The deadliest hurricane in United States history was at Galveston Island, called the Texas Storm of 1900. It was a Category 4 hurricane and there was more than 6,000 deaths occured with this storm.

(Image courtesy of NASA.)






Hurricane Andrew



A picture of Earth.
Vitals:
Hurricane Andrew cost the United States more than $25 billion dollars. Andrew also claimed 26 lives and left more than 250,000 people homeless. It lasted eleven days from August 16-27, 1992 and hit land in the Bahamas, southern Florida, and southcentral Louisiana. This particular hurricane originated off the West Coast of Africa in early August, 1992. On August 17, 1992 it became a tropical depression halfway between Africa and the eastern islands of the Carribean. Later on that day thunderstorms began to form within it and shortly after, the storm reached tropical storm status. The storm then began to move very quickly and it's strength fluctuated for the next few days. On August 21 it gathered more strength and at 5AM on August 22 it reached hurricane status. At 12:48PM on August 23 the hurricane reached Category 4 status. Later on that evening the eye of the storm passed over the Bahamas and the maximum wind gust was measured to be 120 mph. However, when it passed over the Bahamas it began to weaken. Finally, on the morning of August 24 it struck southern Florida. The winds were reported to be up to 140 mph. Eventually, on August 25 Andrew entered the Gulf of Mexico. The hurricane was severly weakened and later on that day it curved northward and struck land in south-central Louisianna. While over Louisiana it was down graded from a Category 4 hurricane to a Catergory 3. While making it's destructive path through Louisianna, it spawned a tornado that had a damage path 9 miles long and 150 yards wide. Finally it was downgraded to a tropical storm near Bayton Rouge and Layfayette, Louisianna.

(Image courtesy of NASA.)




An over view of the damage caused by Hurricane Andrew.
Damage, Costs, and Deaths:
Hurricane Andrew was the third strongest hurricane to hit the United States in the 20th century and the largest to hit Florida in 30 years. Andrew was also the most expensive natural disaster to ever hit the United States. It cost over $25 billion dollars to repair the damages. On it's rampage through the Bahamas, Florida, and Louisiana it killed 26 people, 15 in Dade County, Florida, and left another 250,000 homeless. In southern Dade county the hurricane destroyed 25,524 homes and damaged 101,241 others. In total, there were approximately 600,000 homes and businesses destroyed or severly damaged by the waves, winds, and rain from Andrew. Over 1.4 million people were left without power and some went with out it for up to six months. It was also estimated that ninety percent of all the mobile homes in South Dade County were totally destroyed and in Homestead, Florida 1167 mobile homes out of the 1176 were destroyed completely. It could have been worse, however, if Hurricane Andrew would have struck 20 miles North in Miami, Florida, a city of 1.9 million people. This would have surely raised the death toll and cost tremendously.

Another picture of the damage caused by Hurricane Andrew.

(Images courtesy of NOAA.)




Ecological Effects: Hurricane Andrew not only hurt the human stuctures, but it hurt Mother Nature too. Florida is the home of the wetlands and Andrew managed to pass right through the center of them. The most obvious damage caused there, like everywhere else, was the structural damage (i.e. uprooting trees). The most damage to trees was done in Biscayne National Park and Everglades National Park. In those parks many of the Mangrove trees, on approximately 70,000 acres, were severly damaged or knocked down. All in all, almost any large tree in the storm's path was badly damaged. Andrew did not have much effect on the wildlife, however. Most of the animals survived through the storm and the regrowth of vegetation. The Northern Florida Keys did not escape do as well as the Wetlands. The Northern Keys were completly stripped of vegetation.

On the coast of Louisiana 70 kilometers of sand was stripped off the barrier islands exposing old coastal marsh. Also, over 80 percent of the oyster reefs off the Louisiana coast had between 0.3-0.9 meters of sediment taken away. Finally, more than 70 percent of the dunes used to protect the wetlands and coastal population were also swept away. This just shows that not only were people's homes, communities, and businesses effected by this storm, but many other things were too.



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Nicole Dix/ldix@email.arizona.edu/Revised December 2, 2001