Hurricanes In Brief
Hurricanes and typhoons are large and sometimes intensely violent storm systems. In meteorological terms, they are tropical cyclones that have maximum sustained winds of at least 120 km/h (75 mph). Atlantic and eastern Pacific storms are called hurricanes, from the West Indian huracan ("big wind"), whereas western Pacific storms are called typhoons, from the Chinese taifun, "great wind."
The primary energy source for a tropical cyclone is the latent heat released when water vapor condenses. Only extremely moist air can supply the energy necessary to spawn and maintain tropical storms, and only very warm air contains enough moisture. Tropical cyclones, therefore, form only over oceans with water temperatures of at least 27 degrees C (80 degrees F). After they have formed, such storms tend to intensify when passing over warmer water and weaken over colder water.
The rate of condensation heating that results from the intense rainfall associated with tropical cyclones is about 10 to the eleventh power kW. In one day, therefore, a storm produces 24 x 10 to the eleventh power kW h, an amount of energy that lies within the range of the yearly consumption of power by many industrialized nations.
Structure of the Storm
The mature tropical cyclone is characterized by a circular pattern of stormclouds and torrential rains, whipped by winds that may reach velocities of 160 to 300 km/h (100 to 180 miles per hour) within a radius of 10 to 100 km (6 to 60 mi) from the storm center. The winds diminish rapidly with increasing distance. At a radius of 500 km (300 mi), wind speed is usually less than 30 km/h (18 mph). (The winds rotate in a counterclockwise direction in the Northern Hemisphere and in a clockwise direction in the Southern Hemisphere.) The heaviest precipitation occurs in this region of intense convection. Thunderstorms may produce rainfall rates of 250 mm (10 in) a day. The release of latent heat...
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