Climate of India and the Monsoon Mechanism: Seasons, Local Winds and Rainfall

Drafted with AI assistance and fact-checked on 28 October 2026; not yet read line by line by a human editor. Spotted a mistake? Tell us. Editorial standards & corrections

Climate type and controls

India has a tropical monsoon climate, marked by a seasonal reversal of winds and by rain packed into a few months. The word monsoon comes from the Arabic mausim, meaning season. Several factors shape it: latitude, since the Tropic of Cancer divides the country into a tropical south and a sub-tropical north; the Himalayas, which block the cold winds of Central Asia; pressure and winds; distance from the sea, which gives coastal places an even climate and interior places such as Delhi extremes of heat and cold; relief, which makes windward slopes wet and leeward slopes dry; and the jet streams of the upper air. The India Meteorological Department (IMD) was set up in 1875, and meteorologists divide the Indian year into four seasons.

The four seasons

The cold weather season (December to February) brings clear skies and dry north-east winds blowing from land to sea. Western disturbances, low-pressure systems that start over the Mediterranean Sea and travel east with the westerly jet stream, bring light winter rain, locally called mahawat, to Punjab, Haryana, Delhi and western Uttar Pradesh and snow to the hills; this rain is valuable for rabi wheat. The hot weather season (March to May) brings rising heat that moves north with the sun. The advancing monsoon or rainy season lasts from June to September, and the retreating monsoon or post-monsoon season covers October and November.

Local winds of the hot season

The loo is a hot, dry, gusty wind that blows over the northern plains from Punjab to Bihar on May and June afternoons. Kalbaisakhi or nor'westers are violent evening thunderstorms in West Bengal and Assam; in Assam they are called Bardoli Chheerha. They help tea, jute and rice. Mango showers are pre-monsoon showers on the coasts of Kerala and Karnataka that help mangoes ripen early, and blossom showers make coffee plants flower. Dust storms called aandhi are common in Rajasthan, Punjab and Haryana.

The monsoon mechanism

In summer the land heats much faster than the sea, so an intense low-pressure area forms over north-western India and Pakistan while the Indian Ocean stays under higher pressure. The Inter Tropical Convergence Zone (ITCZ) shifts north over the Ganga plain, where it is called the monsoon trough. The south-east trade winds of the southern hemisphere cross the Equator, are turned to the right by the Coriolis force and arrive as the south-west monsoon. The heating of the Tibetan plateau, the shift of the subtropical westerly jet stream to the north of the Himalayas, and the Tropical Easterly Jet over the peninsula all help the monsoon set in. El Nino, the periodic warming of the eastern Pacific off Peru, linked with the pressure see-saw called the Southern Oscillation, often weakens the Indian monsoon and brings drought, while a positive Indian Ocean Dipole tends to help it.

Onset, branches, break and retreat

The monsoon reaches the Kerala coast around 1 June with a sudden heavy downpour called the burst, and covers the whole country by early to mid-July. It comes in two branches. The Arabian Sea branch strikes the Western Ghats, drenching the windward side while the Deccan interior lies in the rain-shadow. The Bay of Bengal branch hits Myanmar and Bangladesh, sweeps into the north-east, where the funnel-shaped Khasi hills give Mawsynram and Cherrapunji (Sohra) their huge rainfall, and is turned west by the Himalayas along the Ganga plain, so rain decreases from east to west: about 119 cm at Kolkata, 105 cm at Patna, 76 cm at Prayagraj and 56 cm at Delhi. The Tamil Nadu coast stays fairly dry in this season because it lies parallel to the Bay branch and in the rain-shadow of the Arabian Sea branch. Breaks are dry spells within the rainy season, often when the monsoon trough moves to the Himalayan foothills. From September the monsoon withdraws from the north-west; October brings humid heat called the October heat, and the north-east or retreating monsoon then gives Tamil Nadu most of its rain, while cyclones strike the east coast.

Rainfall distribution

About three-fourths of India's rain falls in the four monsoon months, and the average annual rainfall is about 125 cm, but it varies widely. More than 200 cm falls on the west coast and Western Ghats, the north-east hills and the Andaman and Nicobar Islands, and over 400 cm in parts of Meghalaya, where Mawsynram records the highest average rainfall in the world. Western Rajasthan, Kachchh and Ladakh get less than 50 cm, and parts of Ladakh and western Rajasthan get less than 10 cm, the driest in India. Low-rainfall areas also have the most uncertain rain.

Key facts

Climate controls: latitude, the Himalayan barrier, pressure and winds, distance from the sea, relief and jet streams; IMD was set up in 1875.
Four seasons: cold weather (December-February), hot weather (March-May), advancing monsoon (June-September), retreating monsoon (October-November).
Western disturbances: born over the Mediterranean, carried by the westerly jet; winter rain (mahawat) in Punjab, Haryana, Delhi and western UP, good for rabi wheat.
Local winds: Loo (hot, dry; northern plains), Kalbaisakhi or nor'westers (Bengal and Assam; Bardoli Chheerha in Assam), mango showers (Kerala and Karnataka), blossom showers (coffee).
Monsoon causes: land-sea heating contrast, ITCZ moving north as the monsoon trough, SE trades crossing the Equator and turning SW (Coriolis force), Tibetan heating, Tropical Easterly Jet.
El Nino (warm eastern Pacific) with the Southern Oscillation (ENSO) often means a weak monsoon; a positive Indian Ocean Dipole helps the monsoon.
Onset in Kerala about 1 June (burst); two branches, Arabian Sea and Bay of Bengal; Ganga plain rain falls east to west: Kolkata 119 cm, Patna 105, Prayagraj 76, Delhi 56 cm.
Tamil Nadu gets most of its rain from the north-east (retreating) monsoon in October to December; October heat follows the withdrawal.
Rainfall: average about 125 cm; over 400 cm in Meghalaya (Mawsynram wettest); under 10 cm in parts of Ladakh and western Rajasthan.

Quick revision

Tropical monsoon climate; monsoon from Arabic mausim; IMD set up 1875; seasons: Dec-Feb cold, Mar-May hot, Jun-Sep SW monsoon, Oct-Nov retreat; western disturbances from the Mediterranean bring winter rain for wheat; loo, Kalbaisakhi (Bardoli Chheerha), mango showers; ITCZ, Coriolis, Tibetan heating, Tropical Easterly Jet; El Nino weakens monsoon; onset Kerala about 1 June; Tamil Nadu rain Oct-Dec; average rain about 125 cm; Mawsynram wettest; Ladakh and western Rajasthan driest.

Practise this topic

All 10 lessons on Indian Geography: Physical, Economic and Human