Sep 1, 2010

"What Is...?" Wednesday

What do they mean by "category" when speaking about hurricanes?

When categorizing hurricanes, cyclones, and typhoons scientists had to find a way to identify the different Categorys of intensity in regards to damage and severity. Based upon
the maximum wind speeds and storm surge, a hurricane scale was created, which ranges from Category One to Category Five. The Saffir-Simpson Hurricane Scale was created to monitor and categorize the intensities of hurricanes, cyclones, and typhoons.

When analyzing the intensity of these storms, meteorologists review their maximum wind speeds and the storm surge. A storm surge is the rush of water that comes onshore from a low-pressure storm, like those in a tropical cyclone. Usually, it is the high winds of the storm that push the water further onshore. The Saffir-Simpson Hurricane Scale is used to categorize hurricanes affecting the United States, but other places in the world use other means of rating their storms. The scale does not take into consideration the amount of rainfall or location, which means that a Category 2 hurricane that hits a major city will likely do more damage than a Category 5 hurricane that hits a rural area.

Category One storm’s are considered to be pretty weak and tend to create the least amount of damage to trees, shrubs, and mobile residences. Storms within the Category One category will reach wind speeds between 74-95 miles per hour and their storm surge will reach 4 to 5 feet. Category Two is considered to be a moderate storm and causes noticeable damage to trees and mobile residences, as well as piers. This type of storm has been known to rip the shingles from roofs and cause further damage to the tops of houses. The wind speeds in a Category Two storm can reach between 96-110 miles per hour and their storm surge reaches 6-8 feet.

Category Three is considered strong and is known for blowing down trees or stripping the leaves from the branches. Mobile residences are more likely to be destroyed within these types of storms and damage to other types of buildings is also likely. Category Three storms reach wind speeds of up to 111-130 miles per hour and the storm surge reaches 9-12 feet. Category Four storms are considered to be very strong with the ability to create extensive damage to houses, including the windows, doors, and roofs. When living close to the shore, the damage will be much more devastating. The chances of flooding are high when this type of storm hits. Category Four storms reach wind speeds of up to 131-155 miles per hour and the storm surge reaches 13-18 feet.

Category Five is considered to be the worst Category of hurricanes, cyclones, and typhoons. Small buildings will be overturned or blown away with the winds from a Category Five storm. The structural damage received by this category hurricane or storm is very severe, with wind speeds reaching 156 plus miles per hour. The storm surge in a Category Five storm is 19 plus feet. It is within this category that Hurricane Katrina was placed with maximum wind speeds of over 175 miles per hour.

The Saffir-Simpson scale is used to give an estimate of the potential property damage and flooding expected along the cost from a hurricane landfall. Wind speed is the determining factor in the scale, as storm surge values are highly dependent on the slope of the continental shelf in the landfall region. A category five, or “catastrophic” hurricane has wind speeds greater than 155 miles per hour and will cause complete failure on roofs of residences and industrial buildings and major damage to structures less than 15 feet above sea Category within 1,500 feet of shore. A category five storm requires evacuation of all residential areas on low-lying ground within 5 to 10 miles of shore.


Witchy Godmother said...

Thank you for sharing. You know I always did wonder.

Anonymous said...

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