The African monsoon is caused by the seasonal wind shift in the area near the equator where winds from the Northern Hemisphere converge with the winds of the Southern Hemisphere. This shift mixes the cool air over the Atlantic Ocean and the hot air of the Sahara Desert. The result is massive rainstorms that supply the arid region of Western Africa with much needed water.
During the summer the Southwestern part of the United States experiences a shift in wind that brings monsoon conditions. This happens most pronouncedly in Arizona where hot winds from Mexico mix with cold air from the north. Thunderstorms develop over the desert and flash flood the plains.
Asia is the original home of the monsoon, especially the Indian subcontinent. Here monsoon circulation involves a wind shift that mixes cool air from the Himalayas in the north with the warm air coming from the Arabian Sea and the Bay of Bengal. Monsoon conditions also sweep to the east over China and Indonesia.
Like many natural phenomena pertaining to Australia, the monsoon here is an exception to the rule. Rather than being caused by a mixture of cold air and warm air, Australian monsoon circulation is dependent on the topography of the land, which acts on sea winds from Southeast Asia to form a meteorological trough that produces storms. The monsoon of Northern Australia is extreme, providing the region with nearly all of its annual rainfall during the summer months.