Dec 02 2010

Hurricane Formation

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Hurricanes can cause a lot of damage to the area where it hits, such as the case with Hurricane Katrina. But what makes a hurricane so destructive? How does it go from being a storm off the coast to a mass killer on land? Using high wind speeds and convection, hurricanes become some of the deadliest storms to the hit the coast.

Hurricanes use convection, the movement of hot and cold air, to create monstrous storms. They begin formation by using hot humid air that rises to the top of the storm. As the air moves closer to the top, it also cools and condenses. When the water vapor condenses, it generates rain as well as heat. (Svarney 1999) This cooling makes the air fall back down to towards the bottom of the storm, where it warms and the cycle starts again. The rising warm air creates pressure at the top of the hurricane. As the now-cooled air falls down, air from near the ocean’s surface quickly fills the space. This creates a low-pressure zone close to the ocean’s surface. The cycle is in motion.

The hurricane has three main parts, the eye, the eye wall, and rain bands. The hot air rises out of the hurricane’s “eye”. The eye is very calm compared to the rest of the storm. (Mogil 2007) As the cool air moves outward, it forms the eye wall. This part of the hurricane is the biggest and is the source of the heavy rainfall, also called the rain bands, that accompanies the storm. As the air rises and falls, more and more clouds are created and the natural movement of the wind causes the hurricane to start spinning. Before it can be officially classified as a hurricane, the storm must reach wind speeds of 74 miles per hour. Hurricanes can have wind speeds up to 150 miles per hour and wind gusts up to 190 miles per hour. (Svareny 1999) The hurricane is unique from other types of storms because it is created solely by warm air. (Mogil 2007)

Hurricanes can’t form anywhere due to the need for hot and humid air. They typically form close to the equator and move west or northwest. In the US, land that is far out into the water or peninsulas are the most prone to being hit by hurricanes. Hurricanes are most common July through October and have a peak season during August and September. This is because the temperature is hotter therefore there is more water vapor in the air to start a hurricane. “Hurricane Alley” is a stretch of warm water through the Atlantic Ocean from the west coast of North Africa to the coast of Central America. This is where many of the hurricanes form.

The strength and direction of a storm determines how dangerous it is. Hurricanes are ranked from Category One to Category Five using the Saffir-Simpson scale. Category Five hurricanes are the largest and most destructive. These hurricanes have wind speeds of over 130 miles per hour and a surge of more than 5.5 meters above normal water levels. Hurricane Katrina was a Category Five storm. This scale also takes the amount of probable damage into consideration. It allows for the public to understand how dangerous the particular hurricane is. Storms that are larger than the average thunderstorm are also given names. This is to distinguish between storms if there is more than one. If a hurricane is particularly destructive the name is retired and will not be used again. To alert the public of an imminent danger, The US National Weather Service announces any “watches” or “warnings” necessary. If a hurricane is not planned to cause immediate danger, then a watch is called. If the hurricane is supposed to come through the town and evacuation might be necessary, then a warning is issued. (Reynolds 2000)

Hurricane Katrina was a Category 5 storm that hit the Gulf of Mexico and destroyed the town of New Orleans, Louisiana. First the devastating hurricane hit Brazil; it was one of the first hurricanes to ever go to Brazil and the first hurricane to even be spotted in the south Atlantic ocean. Hurricane Katrina was estimated to be a Category One storm and Brazilian meteorologists didn’t even place in the hurricane category, saying that the wind speeds were only 50 to 60 miles per hour. Hurricane Katrina took a week to evolve into the Category Five storm after the mid-latitude low-pressure system became separated from the jet stream and just stayed off the east coast of Brazil. As it sat over the warm waters, it began to gain strength and moved onto New Orleans. (Mogil 2007) Hurricane Katrina was one of the biggest storms to hit the US in 2006.

One of the most dangerous storms is hurricanes. Using hot moist air, they turn wind into a destructive device that kills and ruins mass amounts of land. Hurricane Katrina was no exception. It used simple warm air and convection to become one of the most destructive hurricanes in history.

By: Sarah Benton

Works Cited

Angelle A. 2010. Hurricane. Discover. (31)8: 18.

Gray W, Klotzbach P. 2006. Causes of the Unusually Destructive 2004 Atlantic Basin Hurricane Season.                     American Meteorological Society. (87)10: 1325-1333.

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McTaggart-Cowan R, Bosart L, Davis C, et al. 2006. Analysis of Hurricane Catarina. Monthly Weather                      Review. (134)11: 3029-3053.

Mogil M. 2007. Extreme Weather. New York (NY): Black Dog & Leventhal. 304.

Reynolds R. 2000. Cambridge Guide to the Weather. Cambridge:  Cambridge University Press. 192.

Svarney T, Barnes-Svarney P. 1999. Skies of Fury. New York (NY): Touchstone. 224.

Tropical Cyclone Climatology [Internet]. Miami (FL): National Hurricane Center; c. 2010 [cited 2010 Jul 14]. Available from:

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