The monsoon is a seasonal modification of the general planetary wind system. Monsoon winds are most powerful India and China. During summer, the interior of Asia become hot and low pressure develops there. On the other hand, the water surface of Indian ocean remains cooler and the pressure gradient is towards the heated interior. So monsoon wind blows from water to land, it is moist and brings lots of rain. In winter the water is warmer than the land surface. As a result, the wind blows from the interior towards the ocean so it is cold and dry.