Climate and Monsoon of India: Seasons, Rain, and Regional Patterns
India’s climate is monsoon climate. Most of the year’s rain arrives in a few summer months on winds from the sea, then the winds reverse. Winters are mostly dry except in the far northwest and the far southeast. Temperature swings from Himalayan cold to Thar Desert heat.
This post explains the seasons, why the monsoon behaves the way it does, and how regions differ. It builds on location, landforms, and rivers. Rain and heat, in turn, decide the vegetation and soils in the last post of the series.
What “monsoon” means#
Monsoon comes from an Arabic word for season. In geography it means a seasonal reversal of wind, not just “heavy rain.” India has a wet summer monsoon and a drier winter monsoon.
The engine is the difference between land and sea. In summer the land heats faster than the ocean. Warm air rises over northern India and pulls in moist air from the Arabian Sea and the Bay of Bengal. In winter the land cools, pressure rises, and dry winds blow out toward the sea.
The Himalaya matters as a wall. It keeps most of that moist air from escaping into Central Asia, and it stops icy continental air from pouring south in winter. Without that wall, north India would look more like a dry continental interior.
The four seasons#
Indian weather writing usually splits the year into four seasons. Dates shift a little by region.
Winter, December to February. The northern plains are cool and often foggy. Nights in Delhi can fall near freezing. Southern India stays warm. Rain is scarce except when western disturbances—storms from the Mediterranean—cross the northwest. Those storms bring snow to the western Himalaya and winter rain to Punjab, which helps the wheat crop.
Summer, March to May. The sun moves north. The interior heats up. Daytime temperatures on the northern plains often pass 40°C (104°F). In the Thar, extremes have gone above 50°C (122°F). Phalodi in Rajasthan recorded 51°C (123.8°F) in May 2016. A hot, dry wind called the loo blows across the northern plains on bad afternoons. Pre-monsoon thunderstorms, sometimes with dust or hail, break the heat locally. In Kerala and Bengal these storms have local names and mark the approach of the rains.
Southwest monsoon, June to September. This is the rainy season for most of the country. It usually begins on the Kerala coast around June 1, spreads up the west coast quickly, and reaches the northwest later in July. By September it starts withdrawing from the northwest. Farmers time rice planting to this arrival. A delay of two weeks can damage a season.
Retreating monsoon, October and November. Winds shift. The northern plains clear and turn pleasant. The Bay of Bengal stays unstable. Tropical cyclones form here more often than in the peak summer months and strike the east coast. Tamil Nadu, which sits in a rain shadow during the summer monsoon, gets much of its yearly rain in these months from the northeast winds. People call that the northeast monsoon.
Two branches of the summer monsoon#
The summer system arrives as two branches.
The Arabian Sea branch hits the Western Ghats head-on. Air rises, cools, and drops heavy rain on the coastal side. Mumbai and the Malabar coast get soaked. East of the Ghats, the Deccan interior is much drier. Pune, only a short distance inland from Mumbai, lives in that rain shadow. The same branch curves north toward Gujarat and Rajasthan, but by then much of the moisture is spent, which is one reason the Thar stays dry.
The Bay of Bengal branch aims at the delta, then is deflected west by the Himalayan wall. It waters the northeast, then the Ganga plain, and finally Punjab. Where this air is forced up the southern slopes of the Meghalaya plateau, rainfall becomes extreme. Mawsynram and nearby Cherrapunji are among the wettest places on Earth. A typical year at Mawsynram brings roughly 11,800 millimeters (about 465 inches). A nearby valley can be far drier, because the rain falls on the first slope the wind hits.
The two branches meet over the northern plains. Breaks in the monsoon—weeks when the rains stall—are as important as the onset. A “break” over the Gangetic plain can wilt rice even in a year that ends with a normal total.
Why some years fail#
A “normal” monsoon is a national average. It can hide a flood in Assam and a drought in Marathwada. The India Meteorological Department compares each year with a long-term average and labels the season normal, excess, or deficient.
Several large patterns tilt the odds:
- El Niño, a warming of the central and eastern Pacific, has often lined up with a weaker Indian monsoon. La Niña has often lined up with a stronger one. The link is real and imperfect. Some El Niño years are still adequate.
- A warmer Indian Ocean can change where the moist air rises, sometimes feeding ocean storms instead of the land.
- The position of the monsoon trough, a low-pressure belt across northern India, decides which region gets the day’s rain.
Climate change does not replace the monsoon, but it is changing the texture. Very heavy one-day falls are becoming more common. That means more urban floods and more dry spells between cloudbursts, even when the seasonal total looks fine.
Regional climates in plain language#
A Köppen-style sketch is enough for a general reader:
- Tropical wet along the western coast, the islands, and parts of the northeast. Rain is high and the dry season is short.
- Tropical wet-and-dry across much of the peninsula. A clear wet summer and a long dry season.
- Semi-arid and arid from the Deccan rain shadow into the Thar and western Gujarat.
- Humid subtropical on the northern plains. Hot summers, cool winters, monsoon rain.
- Mountain climates in the Himalaya, getting colder and drier with height. Ladakh is a cold desert because it sits behind the main ranges.
The same latitude can host two climates. Mumbai and Pune share a latitude and not a rainfall total. Shillong’s hills and the nearby plains do not either. Landform, covered in the physical features post, is the reason.
What the monsoon means for people#
About half of India’s farmland still depends mainly on rainfall rather than assured irrigation. A good monsoon fills reservoirs, recharges wells, and cuts food prices. A bad one hits rural incomes first and city prices next.
Cities feel the monsoon as drainage. Mumbai, Chennai, and Bengaluru flood when a single extreme day exceeds what drains and lakes can hold. Hill towns face landslides when saturated slopes give way. The 2013 Uttarakhand floods and the 2018 Kerala floods were reminders that steep river basins plus extreme rain are a dangerous mix.
For a visitor from the United States, the practical translation is simple. November to February is the comfortable season for most of the north and the tourist circuits. The southwest coast is lush but very wet from June to September. The Thar is best in winter. Ladakh’s road season is roughly late spring to early autumn, between snow closure and the hardest freezes.
How to read a monsoon headline#
Ask four questions:
- Onset or total? A late start and a normal total are different problems.
- Which region? A national “normal” can drown one state and dry out another.
- How many heavy days? Three cloudbursts are not the same as steady rain.
- Which crop season? Kharif crops (rice, cotton, millets) depend on summer rain. Rabi crops (wheat, mustard) depend on leftover moisture and winter showers.
Keep a personal log if you are studying this for class: date of Kerala onset, date the rains reach your city of interest, and one note on floods or breaks. Export the log as a PDF and attach a rainfall map with Merge PDF.
FAQ#
When does the monsoon start in India?#
The southwest monsoon usually reaches the Kerala coast around the first of June. It can be several days early or late. Northwest India typically waits until July.
Why is the Thar Desert dry if monsoon winds pass nearby?#
The Arabian Sea branch drops much of its rain on the Western Ghats and the west coast. Air that reaches Rajasthan is drier. The Aravalli Range is also too low and poorly aligned to squeeze out a second big rainfall. High heat and low humidity do the rest.
Does all of India get rain in summer?#
No. The interior of Tamil Nadu gets relatively little summer rain because it is on the lee side of the Western Ghats for southwest winds. Its main rainy season is October to December.
What is a western disturbance?#
It is a storm system that travels from the Mediterranean region into northwest India and Pakistan, mostly in winter. It brings rain to the plains and snow to the mountains.
Where to go next#
Rain and temperature draw the vegetation map. The last post in this series covers India’s forests, wildlife regions, and soils, and how each one lines up with the climates above.