Hurricanes originate over tropical waters, close to the equator.
If the atmosphere is calm and the water is warmer than about 27 C, evaporation forces large amounts of moisture into the air, creating a low-pressure system. When this water vapour condenses, it releases heat that powers the circular winds that characterize a hurricane. Rainfall in the developing storm releases more heat, triggering a convection process that pulls more moisture-laden air up through the centre of the system. The storm grows via this feedback mechanism, and, in the northern hempisphere, because of the Earth's rotation, the system moves from east to west before curving northward. In the eye of the hurricane, air is sucked upward faster than it can rush in at the bottom.