The high temperatures of the tropical regions generates a water cycle whereby the accelerated evaporation of water results in high levels of rainfall.
Tropical Rain forests receive at least 2000 mm of rainfall per year.
The climate of equatorial regions are heavily influenced by the Inter-tropical Convergence Zone, or ITCZ. The ITCZ is the region near the equator, where the northeast trade winds and the southeast trade winds converge forcing air up into the atmosphere.
This is aided by the fact that the intense solar heating of the tropics heats the ground, forcing warm air to rise through convection. The air cools as it rises causing water vapor to condense into clouds, which eventually leads to convectional precipitation. These storms are often heavy but are over relatively quickly.
The position of the ITCZ changes seasonally. It moves north in the northern hemisphere summer and south in the northern hemisphere winter. (Southern Summer) This is what is responsible for the wet and dry seasons in tropical regions. In the Northern Hemisphere, the wet season occurs from May to July, in the Southern Hemisphere from November to February.
This video was made in Thailand.

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