The Intertropical Convergence Zone (ITCZ) is a region that circles the Earth near the equator, where the trade winds of the Northern and Southern Hemispheres converge. It is also known as the doldrums or the calms because of its monotonous windless weather. The intense sun and warm water of the equator heat the air in the ITCZ, raising its humidity and making it buoyant. Aided by the convergence of the trade winds, the buoyant air rises. As the air rises, it expands and cools, releasing the accumulated moisture in an almost perpetual series of thunderstorms. The ITCZ was originally identified as the Intertropical Front (ITF) from the 1920s to the 1940s, but after the recognition in the 1940s and the 1950s of the significance of wind field convergence in tropical weather production, the term Intertropical Convergence Zone (ITCZ) was then applied.

The ITCZ appears as a band of clouds consisting of showers and occasional thunderstorms that encircles the Earth near the equator. Seasonal shifts in the location of the ITCZ drastically affect rainfall in many equatorial nations, resulting in the wet and dry seasons of the tropics rather than the cold and warm seasons of higher latitudes. Longer-term changes in the ITCZ can result in severe droughts or flooding in nearby areas. The ITCZ shifts north and south seasonally with the Sun, and over the Indian Ocean, it undergoes especially large seasonal shifts of 40°–45° of latitude. As the ITCZ migrates to tropical and subtropical latitudes and even beyond during the respective hemispheres summer season, increasing Coriolis force makes the formation of tropical cyclones within this zone more possible.