Hurricanes, cyclones, and typhoons are a major hazard in the Tropics. Every year, some 80 occurrences claim, on average, 20 000 lives and cause immense damage to property, natural vegetation, and shipping.
             A hurricane is a large rotating storm around a centre of very low pressure with values of 950mb or lower. Most systems have a diameter of about 650km, less than half that of a mid-latitude depression. Wind speeds often exceed 33m per second (119km per hour) and, in the most intense hurricanes like Andrew, may reach 50m per second (1 8Okm per hour). The huge amount of heat required to create and maintain the hurricane is reflected in the height of the clouds near its centre, often up to ]2km above the Earth.
             A number of trigger mechanisms, which rely on intensive rising convection currents, are required to transform a tropical disturbance into a more destructive hurricane. The development of a hurricane is dependent on combinations of particular.mechanisms.
              An extensive ocean area with surface temperatures greater than 27 "C for a significant period of time.
              Sufficient spin from the Earth's rotation to trigger the vicious spiral in the centre of the hurricane, usually between latitudes 50 and 30cl north and south of the Equator.
              A lack of strong horizontal air movement or wind shear, near a jet stream for example, which causes the break-up of the spiralling winds.
              Where upper-air winds in the troposphere cause a rapid ascent of air to be sucked in at the sea surface to replace that lost above. This causes a rapid upward draught of moisture-laden air, which in turn produces huge volumes of condensation to form massive clouds.
             As trade winds rush into the centre of the storm, they spiral inwards and upwards, releasing heat and moisture. Earth's rotation twists the rising columns of air into a whirling cylinder around an eye of still, cloud-free descendi
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