Tropical CYCLONE formed over the North Atlantic, E North Pacific, W South Pacific, and Indian oceans in which the winds attain speeds greater than 75 mph (121 km/hr). A tropical cyclone passes through two stages, tropical depression and tropical storm, before reaching hurricane force. An average of 3.5 tropical storms per year become hurricanes; one to three of these approach the U.S. coast. Hurricanes usually develop between July and October. A hurricane is nearly circular in shape, and its winds cover an area about 500 mi (800 km) in diameter. As a result of the extremely low central air pressure (around 28.35 in/72 cm of mercury), air spirals inward toward the hurricane's eye, an almost calm area about 20 mi (30 km) in diameter. Hurricanes, which may last from 1 to 30 days, usually move westward in their early stages and then curve northward toward the pole. Deriving their energy from warm tropical ocean water, hurricanes weaken after prolonged contact with colder northern ocean waters, becoming extratropical cyclones; they decay rapidly after moving over land areas. The high winds, coastal flooding, and torrential rains associated with a hurricane may cause enormous damage. Tropical cyclones that form over the E North Pacific Ocean and its seas are called typhoons; those over the Indian Ocean and its seas, cyclones.
Hurricanes.
Tropical CYCLONE formed over the North Atlantic, E North Pacific, W South Pacific, and Indian oceans in which the winds attain speeds greater than 75 mph (121 km/hr). A tropical cyclone passes through two stages, tropical depression and tropical storm, before reaching hurricane force. An average of 3.5 tropical storms per year become hurricanes; one to three of these approach the U.S. coast. Hurricanes usually develop between July and October. A hurricane is nearly circular in shape, and its winds cover an area about 500 mi (800 km) in diameter. As a result of the extremely low central air pressure (around 28.
