A cyclone is a large-scale air mass that rotates around a strong center of low atmospheric pressure. Cyclones are characterized by inward spiraling winds that rotate about a zone of low pressure. The largest low-pressure systems are polar vortices and extratropical cyclones of the mid-latitudes. Tropical cyclones can be much smaller and occur in the tropics.
Cyclonic wind flows mirror the rotation of the Earth, so they rotate clockwise north of the equator and counterclockwise south of it. Low-pressure areas produce light winds near their centers, while high-pressure areas produce strong winds at their circumference. Cyclone rainfall tends to be highly localized and very heavy, often resulting in flooding.
Cyclones typically form over warm ocean waters near the equator where evaporation rates are highest. As moist air rises from these tropical oceans, it encounters cooler air and starts to spin due to differences in temperature and humidity. These rotating masses of air can grow into giant storms hundreds or even thousands of kilometers across.
The most powerful type of cyclone is the hurricane, which forms over the Atlantic Ocean and northeastern Pacific Ocean near Latin America. hurricanes typically have sustained wind speeds greater than 119 kilometers per hour (74 miles per hour) and can bring storm surge flooding several meters deep inland along coastlines. Lesser known but just as destructive are typhoons, which form over the northwestern Pacific Ocean near Asia and typically have maximum sustained winds between 185–220 kilometers per hour (115–137 miles per hour).