Tropical cyclones are largely confined to South China Sea, Bay of Bengal and Gulf of Mexico. Why?
Tropical cyclones form over large bodies of relatively warm water, which increases the suitability of the South China Sea, Bay of Bengal and Gulf of Mexico for the formation of tropical cyclones. A tropical cyclone is sustained through evaporation of water from the oceanic surface, which eventually results in the formation of clouds and rain which accompany a cyclone. Thus, the existence of a large water body is crucial to the formation of a tropical cyclone. This is also one of the reasons why tropical cyclones occur almost exclusively in the tropical seas. The South China Sea, Bay of Bengal and Gulf of Mexico all fall in the Tropical zone, thus, increasing their suitability for formation of tropical cyclones. Additionally, the requirement of warm sea surface temperatures is met with only in the tropical areas. Within the tropical regions itself, tropical cyclones are commonly observed between the latitudes of 10 and 30 and not very near the equator. This is due to the fact that the Coriolis forces, which helps the tropical cyclones rotate, is very weak near the equator.
Also, tropical cyclones typically form near the Intertropical Convergence Zone (ITCZ), which is the point of convergence of the northeast and southeast trade winds. The ITCZ is a very important component because it triggers the rotation of low-level winds which eventually develop into tropical cyclones.