Hurricanes, name applied to migratory tropical cyclones that originate over oceans in certain regions near the equator, and particularly to those arising in the West Indian region, including the Caribbean Sea and the Gulf of Mexico. Hurricane-type cyclones in the western Pacific are known as typhoons.

Most hurricanes originate within the doldrums, a narrow equatorial belt characterized by intermittent calms, light variable breezes, and frequent squalls, and lying between the northeast and southeast trade winds. As the doldrums of the Atlantic are situated largely to the north of the equator, hurricanes do not occur in the South Atlantic Ocean. The Pacific doldrums extend north and south of the equator; thus hurricanes occur in the South and North Pacific oceans.

Hurricanes consist of high-velocity winds blowing circularly around a low-pressure center, known as the eye of the storm. The low-pressure center develops when the warm, saturated air prevalent in the doldrums is underrun and forced upward by denser, cooler air. From the edge of the storm toward its center, the atmospheric pressure drops sharply and the wind velocity rises. The winds attain maximum force close to the point of lowest pressure (about 724 torr, or about 28.5 in. of mercury). The diameter of the area affected by winds of destructive force may exceed 240 km (150 mi). Gale winds prevail over a larger area, averaging 480 km (300 mi) in diameter. The strength of a hurricane is rated from 1 to 5. The mildest, Category 1, has winds of at least 120 km/h (74 mph). The strongest (and rarest), Category 5, has winds that exceed 250 km/h (155 mph). Within the eye of the storm, which averages 24 km (15 mi) in diameter, the winds stop and the clouds lift, but the seas remain very violent.

Hurricanes generally move in a path resembling the curve of a parabola. In the northern hemisphere the storms usually travel first in a northwesterly direction and in the higher latitudes turn toward the northeast. In the southern hemisphere the usual path of the hurricane is initially to the southwest and subsequently to the southeast. Hurricanes travel at varying rates. In the lower latitudes the rate ranges from 8 to 32 km/h (5 to 20 mph) and in the higher latitudes it may increase to as much as 80 km/h (50 mph). Those areas in which the hurricane winds blow in the same direction as the general movement of the storm are subjected to the maximum destructive violence of the hurricane.

Since 1943 U.S. military aircraft have been flying into hurricanes to measure wind velocities and directions, the location and size of the eye, the pressures within the storms, and their thermal structure. A coordinated system of tracking hurricanes was developed in the mid-1950s, and periodic improvements have been made over the years. Radar, sea-based recording devices, geosynchronous weather satellites (since 1966), and other devices now supply data to the National Hurricane Center in Florida, which follows each storm virtually from the beginning. Improved systems of prediction and communication have been able to help minimize loss of life in hurricanes, but property damage is still heavy, especially in coastal regions. The strongest hurricane to hit the western hemisphere in the 20th century, Gilbert, devastated Jamaica and parts of Mexico in 1988 with winds that gusted up to 350 km/h (218 mph). Destructive hurricanes in recent U.S. history include Hugo (1989), with $4.2 billion in damage and more than 50 deaths, and Andrew (1992), with $15.5 billion in damage, more than 50 dead, and thousands left homeless.

Florida Keys

Florida Keys
Florida Keys, chain of islands, islets, and reefs, southern Florida, between the Straits of Florida and Florida Bay, extending southwest and west from Virginia Key, south of Miami Beach to the Dry Tortugas, for 309 km (192 mi). The keys are chiefly limestone and coral formations. The larger islands of the group are Key West, Key Largo, Sugarloaf Key, and Boca Chica Key. The keys, distributed between Miami-Dade and Monroe counties for administrative purposes, were devastated in a 1935 hurricane. Several of the islands are popular vacation resorts, and fishing and tourism are the leading industries. A causeway extends from the mainland to Key West, the southernmost city of the conterminous United States.