Tropical cyclones, known as hurricanes in the Atlantic and eastern and central Pacific, typhoons in the western North Pacific, and simply tropical cyclones elsewhere, are some of the most potentially destructive storms of our atmosphere. They are the strongest of sequence of rotating tropical stroms of progressively increasing wind strength. A tropical depression is the weakest, and defined as a low pressure system with a closed surface wind circulation with speeds less than 27 konts (50kph). With mean wind sppeeds above 27 konts (50kph) the system becomes known as a tropical cyclone. A tropical storm is a cyclone with mean wind speed between 34 konts (63kph) and 63 knots (117kph)whilst the hurricane or typhoon is a tropical cyclone with speeds of 64 konts and above (118kph).
In recent years hurricanes such as Gloria (1985), Hugo (1989) and Andrew (1992) have caused tremendous damage along the eastern seaboard of the United States but with relatively little loss of life. However, storms of similar intensivity such as david (1979) and Jooan (1988), caused major loss of life in the Dominican respublic and Nicaragua. This differential impact on developed and developing countries in a clear reflection of variations in vulnerability.
Although storms are most obviously associated with high wind speed and even to
Major cyclones are not new. Theyare a characteristic feature of certain areas of the tropics where suitable conditions of hiigh seasurface temperature, high atmospheric humidity and atmospheric wind structure allow their development (Fig. 1). Most cyclones form during the period late sping through to late autumn for each hemisphere. Not all formation areas are equally productive in spawning storms. The western North Pacific produces the greatest number of cyclones,with about 30 per cent of the global total. The Indian ocean is also important, with the Atlantic and East Pacific storms being slighty less frequent. Interestingly, no storms develop in the tropical So
This does not mean the number of storms in any years or decade is constant. The long- term average (1885-1990) for tropical storms and hurricanes in the Atlantic region is about 8 per year.
Research in the United States has indicated a strong relationship between tropical cyclone fr
Although tropical storms affect many parts of world, knowledge of their impact varies. In developed countries, such as the united states, Japan and Australia, loss of life and estimated direct and indirect costs of a storms are soon known. In developing countries, however, the national infrastructure is such that similar information either cannot be produced or takes takes much longer to be determined. Many damaged properties will not have been insured and even the number of people living in an area may nor be known precisely. The amount of the damage for any given storm will be influenced by its severity and by the number of people living along its track. Equally important are the living standarts of
With data from geostationary satellites, the formative stages of major hurricanes can be followed. Improved computer- modeling techniques of hurricane development have allowed more precision as to the areas likely to be affected. With improved communications, such forecasts can be convertes into broadcast warnings and the affected population evacuated.