Saturday, 16 June 2007

Natural disasters: Hurricanes

Hurricanes are severe tropical storms that form in the southern Atlantic Ocean, Caribbean Sea, Gulf of Mexico, and in the eastern Pacific Ocean. Hurricanes gather heat and energy through contact with warm ocean waters, which must be at least 27° on the surface which allows the seawater to evaporate and increased the power of the hurricane. As soon as hurricanes move over land they lose the source of power and gradually weaken as no more water is being evaporated. Hurricanes rotate in a counter clockwise direction in the northern hemisphere and clockwise in the southern hemisphere.

Hurricane-like storms are called by different names in the different regions of the world. For example, the name "hurricane" is given to systems that develop over the Atlantic or the eastern Pacific Oceans. In the western North Pacific and Philippines, these systems are called "typhoons" while in the Indian and South Pacific Ocean, they are called "cyclones".

Hurricanes are part of a family of weather systems known as "tropical cyclones." Hurricanes are classified as "hurricanes" if there wind speed reaches 75mph. A hurricane begins its life as a disorganized storm system which forms over warm, tropical waters in the Atlantic. When the storm system become more organized, it is classified as a "tropical depression," and given a number by the National Hurricane Center. If the winds in a tropical depression grow in intensity to 40mph, it is re- classified as a "tropical storm," and it receives a name.

The winds of a hurricane are structured around a central "eye", which is an area that is free of clouds and relatively calm. Around this "eye" area, storm clouds wrap in a counter-clockwise motion. This "eyewall" of clouds, wind and rain, is the most destructive part of the storm. In fact, it is the eyewall that creates the eye, since the rapid spinning clouds in the wall reduce the pressure in the eye and suck out any clouds that may be there. Hurricanes are usually compact storms, with maximum wind velocities extending out 10 to 100km from the eye. Of course, one can still experience gale-force winds as much as 300 miles out from the eye.

Hurricanes are classified into five categories, based on their wind speeds and potential to cause damage.
Category One -- Winds 74-95 miles per hour
Category Two -- Winds 96-110 miles per hour
Category Three -- Winds 111-130 miles per hour
Category Four -- Winds 131-155 miles per hour
Category Five -- Winds greater than 155 miles per hour

Hurricane can also spawn tornadoes as well which can cause further damage.

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