ABSTRACT
Hurricanes are classified by their wind speed on a damage-potential scale developed by Herbert Saffir, a consulting engineer, and Robert Simpson, a National Weather Service (NWS) meteorologist, in the 1970s (Table 10.1). The Saffir-Simpson Hurricane Scale is divided into five categories based on the highest 1-minute average wind speed in the storm and was first used for NWS public advisories in 1975.5 A hurricane’s category typically changes as it intensifies or weakens, and all but the weakest hurricanes will have more than one category assigned to them during their lifetime. Meteorologists describe Category 3 through 5 hurricanes as major hurricanes. As a hurricane’s wind speed and, thus, its category increase, the atmospheric pressure in the storm’s center drops. Category 5 hurricanes generally have a central atmospheric pressure of less than 920 millibars (&27.17 in. of mercury measured in a baro meter). The record low pressure for an Atlantic hurricane, 882 millibars (&26.05 in.), was set by Hurricane Wilma in 2005.7
NAMING CYCLONES Only a small percentage of all cyclones are given names, either to identify where they form or to track their movement. Extratropical cyclones, especially those that become snowstorms, are sometimes named for the geographic area where they form (e.g., Alberta Clipper) (see Chapter 9). In contrast, all tropical depressions that develop into tropical storms and hurricanes are given individual names by government forecasting centers. These names are established by international agreement through the World Meteorological Organization (WMO). The standardized naming system adopted by the WMO replaced a patchwork of national practices that once included naming hurricanes in honor of the saint on whose holy day the storm came ashore, the military phonetic alphabet, and the names of weather forecasters’ girlfriends.
