cyclone

A cyclone is a large-scale low-pressure system with inward-spiraling winds around a center of circulation. The term is used in meteorology for different systems; in tropical regions it refers to a tropical cyclone, while extratropical cyclones are mid-latitude systems.

Tropical cyclones form over warm tropical oceans when sea surface temperatures exceed about 26.5°C, with sufficient moist air, low wind shear, and a preexisting disturbance. They develop from tropical depressions into tropical storms and then into tropical cyclones, which have sustained winds of at least 119 km/h (74 mph). They exhibit a central eye, an eyewall of intense convection, and rainbands.

Depending on region, tropical cyclones are given different names: hurricanes in the North Atlantic and eastern Pacific; typhoons in the western North Pacific; and simply cyclones in the Indian Ocean and southwest Pacific.

Impacts include strong winds, heavy rain, storm surge, and flooding, leading to property damage, injuries, and loss of life. Forecasts use satellite data, aircraft reconnaissance, radar, and computer models to issue watches and warnings; preparedness measures and evacuation are common.

Lifecycle and movement are driven by steering currents in the atmosphere; some systems stall or move erratically. They typically weaken after moving over land or colder water and may transition to extratropical cyclones with a different structure and energy sources.

See also: extratropical cyclone; subtropical cyclone.