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CYCLONES, TORNADOES, HURRICANES, AND MONSOONS We need to know the differences and similarities between land storms (tornadoes) and ocean storms (hurricanes.) Both kinds of storms originate over heated surfaces and blow toward a low pressure center. The hurricane originates over warm water and has a path width of hundreds of miles. The tornado, on the other hand, starts in temperate zones over land, seldom has a width of more than 2 miles and travels much faster than a hurricane. Cyclone is "a type of atmospheric disturbance characterized by masses of air rapidly circulating clockwise in the southern and counter clockwise in the northern hemisphere, about a low-pressure center, usually accompanied by stormy, often destructive, weather." (American Heritage Dictionary) A hurricane is a "tropical cyclone formed over the North Atlantic, E. North Pacific, and West South Pacific oceans in which the winds attain speeds greater than 75 miles per hour. 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 miles 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 miles 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 hur- ricane 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, are called "cyclones." Tornadoes, are dark, funnel-shaped clouds containing violently rotating air that develops below a heavy cumulo- nimbus** cloud mass and extends toward the earth. The diameter of a tornado varies from a few feet to a mile; the rotating winds reach velocities of 200 to 300 miles per hour, and the updraft at the center may reach 200 miles per hour. In comparison with a cyclone, a tornado covers a much smaller area but is much more violent and destructive. The atmos- pheric conditions required for the formation of a tornado include great thermal instability, high humidity, and the convergence of warm, moist air at low levels with cooler, drier air above. Tornadoes occurring over water are called "waterspouts." (C.C. Encyclopedia) ** ("KEUM-you-low-NIM-bus"; an extremely dense, vertically developed cumulus cloud with a relatively hazy outline and a glaciated top, usually producing heavy rain, thunderstorm, or hailstorm. American Heritage Dictionary.) Cyclone is often called a "low," of low central atmospheric pressure relative to the surrounding pressure. The resulting pressure gradient, combined with the coriolis effect, causes air to circulate about the center, or core...The frictional drag on near-surface air moving over land or water causes it to spiral inward toward lower pressures; this movement is compensated for near the center by rising currents, which are cooled by expansion when they reach the lower pressures of higher altitudes. The cooling, in turn, characteristically increases the relative humidity greatly and produces cloudiness. An anticyclone has the opposite characteristics: a "high," or region of high central pressure relative to the surrounding pressure; descending and diverging air that is warmed by compression as it encounters higher pressure at lower altitudes; and characteristic low humidity and little cloudiness. Both cyclones and anticyclones move across the land at speeds of 500 to 1,000 miles per day. The term cyclone is also used for a tropical storm of the Indian Ocean and a tornado." (C.C. Encyclopedia) Monsoon is a "wind that changes direction with the seasons. Monsoons are the result of differing air pressures caused by the varied heating and cooling rates of continental land masses and oceans. Winter monsoons associated with India and Southeast Asia are generally dry; summer monsoons in those regions are extremely wet." (C.C. Encyclopedia) In India, the monsoon is called "a season of winds." Some areas of India receive 38 feet of rain per year during the summer monsoon.  Any problems with this page? Send URL to
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