Geography

Indian Monsoon: Onset, Mechanism and Withdrawal

The Indian monsoon is a seasonal reversal of winds. The southwest monsoon normally reaches Kerala around 1 June and brings about three-fourths of India's annual rainfall. It splits into the Arabian Sea branch and the Bay of Bengal branch and withdraws from the north-west from around September.

Last reviewed 2026-10-15

Mechanism in brief

In summer the land heats up faster than the sea, creating low pressure over the north-west of the subcontinent. The Inter-Tropical Convergence Zone (ITCZ) shifts north and draws moist winds from the Indian Ocean.
Heating of the Tibetan Plateau and the shift of the subtropical westerly jet to the north help the sudden onset.
El Nino, which warms the central Pacific, is usually linked to a weaker monsoon, and the Indian Ocean Dipole can strengthen or weaken that effect.

Seasons and regions

Four seasons: winter, summer, southwest monsoon and retreating monsoon.
Retreating monsoon (October to November) brings northeast monsoon rainfall to Tamil Nadu and nearby coast.
Western disturbances bring winter rain to north-west India, which helps rabi crops.
Mawsynram and Cherrapunji in Meghalaya are among the wettest places on earth.
The India Meteorological Department (IMD) issues the monsoon forecast.

Frequently asked questions

When does the southwest monsoon normally reach Kerala?

Around 1 June.

What are western disturbances?

Extratropical weather systems that bring winter rain and snow to north-west India.

Which phenomenon is linked to a weaker monsoon?

El Nino, the warming of the central and eastern Pacific Ocean.