The primary reason for the north-east monsoon in South Asia is the seasonal reversal of winds, which occurs due to changes in atmospheric pressure. During the winter months, the landmass of the Indian subcontinent cools, leading to higher pressure. As a result, winds blow from the northeast, bringing moisture-laden air from the ocean. This phenomenon usually occurs between October and December, resulting in rainfall that is crucial for agriculture in the region. It contrasts with the south-west monsoon that occurs during the warmer months.