What is a hurricane?

A hurricane is a large, powerful tropical cyclone that forms over warm ocean waters, typically above 26.5 degrees Celsius, which supply the heat and moisture that fuel it. Warm, moist air rises and spirals inward, and the rotation of the Earth twists the storm into a huge circular system with bands of thunderstorms around a calm centre called the eye. Hurricanes are rated from Category 1 to 5 on the Saffir-Simpson scale based on wind speed, with the strongest exceeding 250 kilometres per hour. The same type of storm is called a typhoon in the western Pacific and simply a cyclone in the Indian Ocean and around Australia.