Hurricanes and other forms of tropical cyclones are often measured on the Beaufort Wind Force Scale. It was created in 1806 by and named after British hydrographer Admiral Sir Francis Beaufort. The scale evolved from previous theories about wind speed and conditions. The scale of 13 numbered classes (zero to 12) is based on qualitative wind conditions rather than wind speed. (The additional numbered classes 13-17 are sometimes used--primarily in China and Taiwan--for particularly strong cyclones.) It became a standard measurement for the British navy in the 1830s. The Beaufort scale has been upgraded several times; the 1946 scale is based on the empirical formula v=0.836 B 3/2 m/s (v=equivalent wind speed at 10 m above sea surface; B=Beaufort scale number).
The Saffir–Simpson Hurricane Scale is also used for some hurricanes in the Western Hemisphere, using a five category scale of 1 to 5 distinguished by the intensities of sustained winds. A Category 1 hurricane must have a minimum of 74 mph maximum sustained winds; the strongest, Category 5, must exceed winds of 155 mph. The Saffir-Simpson scale is most often used for Atlantic Ocean storms.
The Saffir-Simpson scale ranks the relative intensities of hurricanes. A rating of 5 on the scale represents the worst storm possible, a 1 is the least severe. Categorry 5 storms are rare. Only three have hit the continental U.S.
Hurricane damage is divided into 3 classes: storm surge, wind damage, and inland freshwater flooding. Storm surge is a dome of water 40-50 miles wide that hits the coast where the eye of the storm makes landfall. Wind damage affects a much larger area than storm surge. Also, tornadoes are often spawned by hurricanes. Inland flooding causes flash floods and mud slides.
The scale is called the Saffir–Simpson Hurricane Scale. It classifies hurricanes by their wind intensity. Tropical depressions and storms that have maximum sustained winds greater than 74 mph are considiered hurricanes.
There are then five classes of hurricanes, each based on the strength of their maximum sustained wind speeds. The classifications, with wind speeds measured in miles per hour, are as follows:
Category 1 74–95
Category 2 96–110
Category 3 111–130
Category 4 131–155
Category 5 equal to or greater than 156