Fort Worth, TX (WiredPRNews.com)—With Gustav and the three-year anniversary of Katrina in the news, here’s an overview of how hurricanes work and how they are classified.
Hurricanes are circular, low-pressure storm systems that spin counterclockwise in the northern hemisphere and require warm, moist ocean air to fuel their ferocious engines. Classified from one to five by their maximum sustained winds on the Saffir-Simpson scale, hurricanes can cause minimal structural damage in category one status to completely destroying buildings as category fives.
For those in the United States, hurricanes begin life as tropical depressions that form in the equatorial region of the Atlantic Ocean during the summer months. A tropical depression, according to the National Oceanic and Atmospheric Administration’s Hurricane FAQ webpage, is a closed weather system with maximum sustained circular wind of 38 miles per hour.
As the tropical depression moves west and slightly north, it pulls more and more heat from the warm sub-equatorial waters into its closed, spinning circular engine. When the tropical depression’s sustained circular winds are between 39 and 73 miles per hour, and it has distinct outer bands of rainfall, then meteorologists classify it as a tropical storm.
Once the circular winds stay between 74 and 95 miles per hour, it then reaches category one hurricane status. If the winds continue to increase in speed, and get between 96 and 110 miles per hour, the hurricane becomes a category two. Hurricanes Lili in 2002 and Isabel in 2003 were category one and two hurricanes, respectively.
Categories three, four and five, according the NOAA website, are called Major Hurricanes. Category threes, like Hurricane Katrina in 2005, have maximum sustained winds between 111 and 130 miles per hour and can cause serious loss of life and structural damage.
Wind speeds of 131 to 155 miles per hour are the sign of a category four, like 2004’s Hurricane Charley. The most powerful is a category five, with maximum sustained winds of over 156 miles per hour. 1992’s Hurricane Andrew is an example of a category five. With each increasing category level, the barometric pressure drops and the storm surge potential increases.