Northeast monsoon

Also called: Winter monsoon · Topic: Climate of India and the Monsoon · NCERT: Class 7, Ch 3 "Climates of India"; Class 7, Ch 1 "The Story of Indian Farming"; Class 9, Ch 3 "Atmosphere and Climate"; Class 11, Ch 4 "Climate"

Meaning

The northeast monsoon (also called the winter monsoon) is the set of dry winds that blow from the north-east, from land to sea, over India in winter, after the ITCZ (Inter Tropical Convergence Zone: the low-pressure belt near the equator where the trade winds of the two hemispheres meet) moves south with the sun. These winds are dry over most of India. But they pick up moisture while crossing the Bay of Bengal, so they bring the main rainy season to the Coromandel coast of Tamil Nadu in October–December.

It matters because Tamil Nadu, Puducherry and Karaikal get ~48% of their yearly rain in this season [5]. Their farming, tanks and reservoirs depend on it.

Explanation

How it forms (cause → process → result)

• The sun moves south:
• After the September equinox (about 23 September), the sun is overhead further south.
• The monsoon trough (the low-pressure belt over the Ganga plain) gets weaker and shifts south with the sun.

• The ITCZ also moves south, towards the equator.

• The winds turn around:

• The moist southwest monsoon slowly withdraws. It leaves the whole country around 15 October [2].

• Winds now blow from the north-east to the south-west, from land to sea. These are offshore winds (winds blowing from land out to the sea).

• Why they are mostly dry:

• They start over the cold, dry land of Central Asia and north India.
• So they carry little moisture and give little rain over most of India.

The exception: rain on the south-east coast

• The winds gain moisture over the sea:
• They cross the warm Bay of Bengal and pick up water vapour.
• They hit the Coromandel coast (the east coast of Tamil Nadu, about 8°N–13.5°N).

• The moist air is pushed up, cools, its water vapour condenses, and it rains.

• Cyclones add most of the rain:

• Cyclonic depressions (low-pressure areas with winds spiralling inward) form over the Andaman Sea and the south-east Bay of Bengal.
• They move west or north-west and cross the east coast.
• These cyclones and depressions give the Coromandel coast most of its rain.

• On average there is about 1 day of very heavy rain per season over this region. These heavy spells come when cyclones, depressions and lows make landfall (cross from sea onto land) on the east coast [5].

• Why Tamil Nadu is unusual:

• In June–September, Tamil Nadu lies in the rain-shadow of the Western Ghats (the dry side of a mountain, away from the wind).
• So it gets more rain in October–December than in the southwest monsoon [3].

Timing and size (IMD data)

Parameter	Value
Easterly winds set in over south-east Peninsula (normal)	14 October [3]
Normal onset over coastal Tamil Nadu and south coastal Andhra Pradesh	20 October [3][4]
Actual onset	15 October 2024; 16 October 2025 [3][4]
Normal withdrawal (long-term average)	4 January, ± about 11 days [3]
Average length of season	~75 days [3]
Tamil Nadu normal October–December rain	~443 mm (442.8 mm) [3]
Share of annual rain, south Peninsular India	~30% [5]
October–December LPA (Long Period Average: the "normal" rain over a long base period), south Peninsular India, 1971–2020	334.1 mm [5]

• South Peninsular India in IMD terms has 5 subdivisions: Tamil Nadu, Puducherry & Karaikal; Coastal Andhra Pradesh & Yanam; Rayalaseema; Kerala & Mahe; South Interior Karnataka [5].
• Forecasting:
• IMD has issued seasonal forecasts for this monsoon since 1998, using statistical models.

• Since 2021 it has also used a Multi-Model Ensemble (MME) system. This combines many climate models, including IMD's own Monsoon Mission Climate Forecast System [5].

• 2026 outlook (issued 30 September 2026): October–December rain over south Peninsular India is likely to be normal (88–112% of LPA) [5].

• Strong El Niño conditions (unusual warming of the eastern Pacific Ocean) exist now and are expected to grow stronger until the end of 2026 [5].
• Neutral IOD conditions are expected (IOD, Indian Ocean Dipole: a difference in sea-surface temperature between the western and eastern Indian Ocean) [5].

Where it occurs

• Main rain belt (NCERT): the Tamil Nadu coast (Coromandel coast), southern Andhra Pradesh, south-east Karnataka and south-east Kerala.
• Chennai: its climograph (Class 9 NCERT) shows October–November as its wettest months.
• Where the cyclones form: the Andaman Sea (east of the Andaman and Nicobar Islands, south of Myanmar) and the south-east Bay of Bengal.
• Where the cyclones hit: the crowded deltas of the Godavari and Krishna (Andhra Pradesh) and the Kaveri (Tamil Nadu). A few turn north to hit West Bengal, Bangladesh and Myanmar.
• Dry zone: north India and most of the country get little rain from these winds.
• Arabian Sea: post-monsoon cyclones are rarer here than in the Bay of Bengal (NCERT). But this is changing as the sea warms [8].

Don't confuse with

• Southwest monsoon: it blows from sea to land in June–September and gets moisture from both the Arabian Sea and Bay of Bengal branches. The northeast monsoon blows from land to sea and gets moisture only from the Bay of Bengal.
• Retreating monsoon: this is the slow withdrawal of the southwest monsoon (October–November), from western Rajasthan to the south-east. The northeast monsoon is the new wind system that takes its place, with onset over coastal Tamil Nadu around 20 October [3].
• October heat: hot, humid weather in north India caused by clear skies and wet land after the rains stop. It is not caused by the northeast monsoon or by moist sea winds.
• Western disturbances: these are low-pressure systems that bring winter rain to north-west India. The northeast monsoon brings winter rain to the south-east coast.

Prelims Hooks

• The northeast monsoon gets its rain from the Bay of Bengal, not the Arabian Sea. Trap: these "dry" winds still bring rain to the Coromandel coast.
• Normal onset over coastal Tamil Nadu and south coastal Andhra Pradesh: 20 October. Normal withdrawal: 4 January [3].
• Tamil Nadu, Puducherry and Karaikal get ~48% of their annual rain in October–December. South Peninsular India gets ~30% [5].
• Tamil Nadu gets more rain in winter than in summer because it lies in the rain-shadow of the Western Ghats in June–September [3].
• Post-monsoon cyclones from the Andaman Sea hit the Godavari, Krishna and Kaveri deltas. Chennai's wettest months: October–November.
• The Arabian Sea had its first post-monsoon extremely severe cyclonic storms (winds >46 m/s) in 2014 and 2015 [6].

Mains Points

• Why the south-east coast gets winter rain (GS-I):
• The ITCZ moves south, so dry offshore northeast winds blow.
• They gain moisture over the Bay of Bengal. Together with Andaman Sea depressions, they bring rain to the Coromandel coast, which is in rain-shadow in summer.

• Result: Tamil Nadu's farming, tanks and reservoirs depend on October–December rain (~48% of its annual rain) [5].

• Disaster risk on the east-coast deltas (GS-III):

• Post-monsoon cyclones hit the crowded, low-lying Godavari, Krishna and Kaveri deltas. They bring storm surge (sea water pushed onto land by storm winds), floods and crop loss.

• Responses: impact-based forecasts and early warnings from IMD, and preparation in advance [5].

• Climate change and shifting cyclone risk (GS-I/III):

• The Arabian Sea's post-monsoon cyclone Genesis Potential Index (a measure of how favourable conditions are for cyclones to form) rose from 1998 to 2021 [7]. Model studies link stronger storms there to human-caused warming [6].
• This puts the west coast (Gujarat, Maharashtra, Kerala) at risk from cyclones that used to be rare. Coastal shelters and warning systems must now cover both seas.

Related concepts

• Retreating monsoon
• October heat

Read more

• The retreating monsoon and the northeast monsoon