Hurricane

Hurricane, tropical cyclone of great intensity. High-speed winds spiral in toward a low-pressure core of warm, calm air (the eye). Winds of over 185 mph (298 kmph) have been measured. The direction of spiral is clockwise in the southern hemisphere and counterclockwise in the northern hemisphere. Hurricanes form over water when there is an existing convergence of air near sea level. The air ascends, losing moisture as precipitation as it does so. If this happens rapidly enough, the upper air is warmed by the water's latent heat of vaporization. This reduces the surface pressure and thus accelerates air convergence. Since they require large quantities of moist warm air, hurricanes rarely penetrate far inland. Hurricanes of the North Pacific are often called typhoons.