What is a hurricane? A hurricane is a tropical cyclone that has a maximum sustained wind of at least 75 mph. The primary energy source for tropical cyclones 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 80 deg F. After they have formed, such storms tend to intensify when passing over warmer water and weaken when passing over colder water. The rate of condensation heating resulting from the intense rainfall associated with hurricanes is about 100 billion kW. In one day, therefore, a hurricane produces 24 X 100 billion kW h, an amount of energy that lies within the range of the yearly consumption of power by many industrialized nations. The mature hurricane is characterized by an eye--a cloud-free circular region of relatively light winds in the center of the storm. The sinking motion in the eye, which causes the clearing, also produces adiabatic warming and drying. Temperatures at 3 mi above sea level are typically 18 deg F warmer than the hurricane's environment. Surrounding the eye, which has a diameter of 6 to 60 mi, the winds in the eyewall rotate counterclockwise at maximum velocity, which may exceed 180 mph in the most severe storms. These winds are maintained by the large differences in horizontal pressure between the eye and the outer region of the storm. Although the winds themselves are responsible for much of the storm damage, the waves and tides generated by the wind often cause most of the damage to coastal areas. In hurricane Camille (1969), for example, the storm surge produced a tide 25 ft above normal as it made landfall near Pass Christian, Miss. Because much of human activity near the coast is concentrated within a few meters above mean sea level, storm sur...
