Traditionally, areas of
tropical cyclone formation are divided into
seven basins. These include the north
Atlantic Ocean, the eastern and western parts of the northern
Pacific Ocean, the southwestern Pacific, the southwestern and southeastern
Indian Oceans, and the northern Indian Ocean (
Arabian Sea and
Bay of Bengal). The western Pacific is the most active and the north Indian the least active. An average of 86 tropical cyclones of tropical storm intensity form annually worldwide, with 47 reaching hurricane/typhoon strength, and 20 becoming intense tropical cyclones (at least of
Category 3 intensity).