Page "Monsoon" Paragraph 8

During warmer months sunlight heats the surfaces of both the land and the oceans, but the land temperature rises faster.

Since the land's surface is warm, the gases expand and an area of low pressure develops.

Since the ocean is at a more moderate temperature, it retains a higher pressure than on land.

This pressure difference causes sea breezes to blow from the ocean to land, bringing moist air.

To complete the cycle, air rises to a higher altitude over land and then flows back toward the ocean.

However, upon rising ( and while still over land ) the air cools, which decreases its ability to hold water, causing precipitation over land.

This is the reason why summer monsoons cause a large amount of rain over land.