Traditionally, tropical cyclones form in 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, super typhoons, or major hurricanes (at least of Category 3 intensity). Scientists initially believed that there were no South Atlantic tropical cyclones, an assertion proved false in 2004 when Cyclone Catarina struck southeastern Brazil. Occasionally, there are tropical-like cyclones in the Mediterranean Sea.
