The Saffir-Simpson Hurricane Wind Scale

The summer months bring the best and the worst of tropical weather. Between the months of June and November, there are sunny skies and beaches and at times, history making storms and hurricanes. As a way of classing tropical cyclones, the National Hurricane Center has used the Saffir-Simpson Wind (Hurricane) Scale and has saved millions of lives and billions in property.

What is the Saffir Simpson Wind Scale?

The Saffir-Simpson Wind Scale is a classification system, similar in concept to the Richter Scale, used primarily in the Western Hemisphere. The system divides hurricanes, tropical cyclones with sustained wind speeds greater than 74 miles per hour (119 kilometers per hour), into five set categories. The categories are distinguishable by wind speeds, storm surge, and potential flooding.

Origin of the Scale

The Saffir-Simpson Wind Scale has been in use since 1973 by the National Hurricane Center. It is named for two men, the late Herbert Saffir and Robert Simpson. Each man made great contributions to the development of this useful system.

Herbert Saffir was educated at Georgia Institute of Technology and received a Bachelors in Civil Engineering in 1940. Soon thereafter, he began working for Dade County Florida Government. Over time, he became a county engineering and helped to develop building codes in the hurricane prone area. By 1965, Saffir was working on a study for a UN commission studying windstorm damage. It was during this time his findings lead him to developa scale to categorize the more intense hurricanes.

Dr. Robert Simpson's life had always been connected to hurricanes. Raised in Corpus Christi, Texas, he almost drowned during a hurricane at almost seven years of age. He received his bachelors and masters in physics from Southwestern University and Emory University, respectively. While a guest of the Air Force, he flew into his first hurricane. Over time, he would become a meterologist and ultimately, the Director of the National Hurricane Center, where he would meet Herbert Saffir.

Simpson and Saffir met and became friends. After Saffir's work with the United Nations, in 1969, Simpson added more information to Saffir's categories. His contribution offered impact of storm surge and central pressure ranges. After this, the scale became known as the Saffir-Simpson Hurricane Scale.

The Scale's first version was used by the United Nations in 1971 and more widely used in 1974 after Simpson had left the National Hurricane Center.

The Saffir-Simpson Categories

Category One is the first class on the scale and is used for those tropical cycles with wind speeds of 74 to 95 miles per hour. This class of Hurricane, which includes the recent Hurricane Hanna, causes minimal damage.

Category Two is the second class on the scales and denotes those storms with minimal wind speeds of 96 miles per hour and maximum wind speeds of 110 miles per hour. This class of storm can cause damage to poorly constructed buildings. Recent Hurricane Alma falls into this class.

Category Three is the mid range class and storms with wind speeds between 111 to 130 miles per hour. Storms of this intensity can cause serious damage and destroy small buildings and cause flooding. Hurricane Bertha and Hurricane Katrina are examples of a tropical cyclone in this category.

Category Four is one the more intense classes on the scale. With winds ranging from 131 to 155 miles per hour, these tropical storms cause incredible devastation and have destroyed homes and flooded towns.

Category Five is the last class on the scale and is used for those storms with sustained winds of more than 156 miles per hour. Flooding, property damage and death are all risks with this class of storm. Hurricane Andrew which made the news in the early 1990s is an example of this class storm.

Other Considerations

The Saffir Simpson Wind Scale is considered a disaster-potential tool for forecasters. While useful, it have come under criticism.

Some think that the Scale does not consider other important variables such as location of the storm or rainfall. The scale also does not consider the impact of tornadoes or rainfall related floods. Considering these variables, could have helped forecasters evaluate the true destructive power of storms such as Katrina.

There have been changes to the scale since 1973. In 2009, the National Hurricane Center eliminated the storm surge and pressure ranges from the categories- which makes the scale simply a wind scale. In 2010, the scale will undergo additional modifications and use a scale which also excludes flood ranges.

Since the 1971, the Saffir-Simpson (Hurricane) Wind Scale has helped meteorologists forecast the impact of intense tropical cyclones. Over the 4 decades the Scale has been in use, communities have learned to better prepare for the summer's most inclement weather.

For those interested in more information about the Saffir-Simpson Hurricane Wind Scale, check out the following resources:

http://www.nhc.noaa.gov/sshws.shtml

http://www.usatoday.com/weather/whurdmg.htm

http://www.weather.gov/infoservicechanges/sshws.pdf