Tropical cyclones, including hurricanes and typhoons, form when calm, warm ocean waters set up a spiraling convection current in the air above the surface. As warm, moist air rises, cooler air moves in to replace it, creating a rotation that eventually builds into a powerful cyclone.
During the early stages of cyclone development, rising warm air brings moisture into the upper levels of the atmosphere, creating clouds and feeding a rain system. Once the air cools, it falls outside the central column of rising air, spiraling as it descends. The rising air in the center of a storm creates a low pressure zone, and outside air rushes in to fill it, drawing more energy into the storm system. As long as the surface conditions remain warm and calm, the storm can grow in strength.
Hurricanes, typhoons and tropical cyclones are all essentially the same type of storm. Cyclones that form in the Atlantic and Eastern Pacific are generally called hurricanes, while those that move through the Western Pacific toward Asia are called typhoons. Storms that form in the Indian Ocean are called cyclones. Each type of storm has its own system of names, managed separately from the others.
Typhoons form near the equator, in the Central to Western Pacific, and their rotation tends to draw them westward. Those that form north of the equator curve to the north, affecting countries, such as the Philippines and Japan, while those south of the equator may threaten Australia and New Zealand.