Cyclone

Tropical cyclones don’t form near the equator or cross it. The western North Pacific is the most active and the largest number of cyclones that reach to very high latitudes. Storms that occur after usually undergo extratropical transition. The eastern North Pacific is bounded by cold water to the north, and so this environmental feature limit the lifetimes of storms in these regions. The Bay of Bengal has about five times as many tropical cyclones as the Arabian Sea. The high mountain ranges and low-lying coastal plains and river deltas make this region extremely vulnerable to tropical cyclones. Southern Hemisphere tropical cyclones are generally weaker than storms in the North Pacific and Atlantic basins; Rarely systems resembling tropical cyclones can occur in the South Atlantic Ocean and off the subtropical east coasts of Australia and southern Africa. Countries that are impacted by cyclones use a monitoring system, and so the World Meteorological Organization (WMO) has chosen official forecasting centers that are responsible to inform people if there is a threat. In the late 1960’s Herb Saffir and Robert Simpson created a classification convention which consisted of relating the observed damage to a North Atlantic cyclone with the peak surface winds or minimum surface pressure and storm surge in vulnerable coastal locations. This convention is known as the Saffir-Simpson Scale, and was used widely around the world. During the 1970’s and 1980’s the central pressure was used as a proxy for wind speed as accurate wind speed measurements from aircraft reconnaissance were not routinely available until 1990. The storm surge scale has been shown to be invalid, as the surge is strongly affected by other parameters such as storm size, local bathymetry, topography, and the storm’s past motion. The Saffir-Simpson scale was updated by the National Hurricane Center (NHC) in early 2010. Tropical cyclones are tropical storms with wind speeds exceeding 17ms-1 and can be located anywhere. The averaging time used to measure the peak winds differs around the globe and so it is difficult to classify them. A tropical cyclone with rotating winds between 17 m s-1 and 32 m s-1 (gale force) is referred to as a tropical storm in the North Atlantic and North Pacific. In the Caribbean and the eastern Pacific, the strongest of these storms are also referred to as hurricanes who have peak wind speeds exceeding 33 m s-1. In the western North Pacific storms of the same intensity are called typhoons. In the Australian region tropical cyclones with peak surface winds exceeding 33 m s-1 are known as severe tropical cyclones. Typhoons in the western North Pacific with peak 1-minute average surface wind speeds in excess of 65 m s-1 are given the designation super typhoon by the US Joint Typhoon Warning Center. In the Atlantic and eastern Pacific, Category 3-5 hurricanes on the Saffir-Simpson scale (peak winds ≥ 50 m s-1) are labeled an intense hurricane. Clement Wragge, an Australian meteorologist was the person who introduced the assigning of names to tropical cyclones in the late 19th century. The Greek alphabet, names of politicians and later the military alphabet were used; until the 1960’s the WMO developed a consistent regionally-applicable naming convention, while the early lists had only women’s names, in the 1970’s both male and female names were used in the language of the countries affected. People’s names are no longer used for storms in the western North Pacific: storm names for this region are drawn from a list of generic words. If a tropical cyclone moves from one region to another, it is typically renamed to the next name on the list in the new region. Tropical cyclones in the western North Pacific are generally known as typhoons (English). Maximum wind speed is used to determine the category of a hurricane, so where a conflict arises between the choice of category for an observed storm, wind speed should be used.