Land and water are of different densities, so the rate of heating and cooling varies. The Indian subcontinent is surrounded by water on three sides. In summer the land mass of India is warmer than the surrounding sea, therefore there is low pressure. The sea is cooler, thereby having higher pressure. So the winds blow from sea to land.

In winter the land has high pressure while the sea has low pressure. Therefore, the winds blow towards the sea. Thus a seasonal reversal of wind direction takes place.