Convection rainfall is what happens when the sun heats a water source to the point that water turns into vapor and rises. By the time it reaches the condensation level, the vapor is usually cool enough to turn back into water and fall in the form of rain.
This process often causes clouds to develop. As the clouds become heavy, the weight of the clouds can cause precipitation, or convection rainfall. The type of clouds formed during the convection process are known as cumulonimbus clouds. Convectional storms occur in many different geographic locations, but are more severe in tropical areas where water sources are abundant and climates are warmer. They are also more severe in warmer mountain regions.