The Northeast Monsoon Explained

The northeast monsoon is India’s winter rainy season, running from October to December, when cool, dry winds blowing off the Asian continent pick up moisture over the Bay of Bengal and rain heavily on the south-eastern coast, especially Tamil Nadu. It is also called the winter monsoon, the retreating-monsoon rainfall in older textbooks, or the post-monsoon season by the India Meteorological Department (IMD). This explainer was last updated on 30 October 2026.

For most of India the northeast monsoon is a minor event, because the southwest monsoon has already delivered the bulk of the year’s rain. For Tamil Nadu, Puducherry, coastal Andhra Pradesh, Rayalaseema and parts of south interior Karnataka and Kerala, however, the northeast monsoon is the main rainy season, and its success or failure decides the state of reservoirs, farms and city water supply for the coming year.

Key Takeaways

• The northeast monsoon is the October to December rainy season that supplies close to half of Tamil Nadu’s annual rainfall.
• The northeast monsoon winds blow from land to sea, but they pick up moisture while crossing the warm Bay of Bengal before reaching the Coromandel coast.
• Bay of Bengal cyclones and depressions, which peak in October to December, produce most of the extreme rain events in the northeast monsoon.
• The northeast monsoon tends to be stronger in El Nino and positive Indian Ocean Dipole years, which is the reverse of the usual relationship for the southwest monsoon.
• The onset of the northeast monsoon over the south-east coast usually coincides with the final withdrawal of the southwest monsoon from the southern peninsula.
• The northeast monsoon fills the reservoirs, tanks and groundwater of south-eastern India, so a weak season can trigger urban water shortages in cities such as Chennai.

What Is the Northeast Monsoon?

The northeast monsoon is the winter phase of the Indian monsoon system, in which dry north-easterly winds from the continent bring rain to south-eastern India between October and December. It is the counterpart of the southwest monsoon, and the two together make up India’s monsoon cycle.

The winds are called northeasterlies because they blow from the northeast. During the southwest monsoon the flow is from sea to land and carries moisture directly. In the northeast monsoon the flow is from land to sea, so the air starts out dry and cold. It becomes rain-bearing only after it crosses the Bay of Bengal and picks up water vapour from the warm sea surface.

This is why the northeast monsoon rains fall mainly on the east-facing coast. The winds arrive there from the sea side, after crossing the Bay of Bengal, and are lifted by the coast and the hills of the Eastern Ghats and the southern peninsula.

Why Does the Northeast Monsoon Happen?

The northeast monsoon happens because the Asian landmass cools in winter, builds a large high-pressure area, and sends winds outward towards the warmer ocean and lower pressure in the south. This is the reverse of the summer heating that drives the southwest monsoon.

The main steps are:

• Continental cooling: As the sun’s overhead position moves south of the equator after the September equinox, northern Asia cools quickly and a strong high-pressure area develops over Siberia and Central Asia.
• Pressure gradient: Air flows outward from this cold high towards the lower pressure over the tropical oceans and the equatorial trough.
• Wind reversal: Over India the surface winds turn from southwesterly to northeasterly, a classic example of seasonal monsoon wind reversal.
• Southward shift of the ITCZ: The Intertropical Convergence Zone, the belt of rising air and cloud near the equator, moves south over the southern Bay of Bengal and the equatorial Indian Ocean, bringing cloud and rain to the southern tip of India.
• Moisture pickup: The winds pass over the warm waters of the Bay of Bengal, gathering enough moisture to produce heavy rain when forced upward by the coast.

When Does the Northeast Monsoon Start and End?

The northeast monsoon normally starts around the third week of October over the south-east coast and continues until the end of December, with some rain lingering into January. The start is declared by the IMD once the southwest monsoon has withdrawn from the southern peninsula and consistent northeasterly winds and rain set in.

Because the onset of the northeast monsoon is tied to the withdrawal of the southwest monsoon, the two events are often announced together. In some years the IMD declares the withdrawal and the onset on the same day. In other years a delayed withdrawal of the southwest monsoon pushes the start of the winter rains into late October or even November.

The season is not uniformly wet. Spells of heavy rain, often linked to a cyclone or depression in the Bay of Bengal, are separated by dry, bright weeks. The rainfall peaks in November across most of Tamil Nadu and often continues through December.

Which Regions Receive the Northeast Monsoon?

The northeast monsoon mainly rains on Tamil Nadu, Puducherry, Karaikal, coastal Andhra Pradesh, Rayalaseema, south interior Karnataka and Kerala, with Sri Lanka also receiving heavy rain. The IMD tracks the season using meteorological subdivisions that include these areas.

The reason Tamil Nadu depends on this season so strongly is geography. The Western Ghats shield Tamil Nadu from the southwest monsoon, leaving it in a rain shadow during summer. When the winds reverse in October, the east-facing coast is suddenly on the windward side and receives the rain.

How Do Cyclones Affect the Northeast Monsoon?

Cyclones and depressions in the Bay of Bengal strongly affect the northeast monsoon because they supply much of its heavy rain, and a single system can deliver a large share of a season’s total within a few days. October to December is the second cyclone season of the North Indian Ocean, after the pre-monsoon months of April to June.

The sea surface is warm after the summer, and the upper-level winds are favourable, so low-pressure areas readily intensify into depressions and cyclones. Many of them track towards the coasts of Tamil Nadu, Andhra Pradesh and Sri Lanka. Well-known examples include Cyclone Gaja in November 2018 and Cyclone Nivar in November 2020 over Tamil Nadu, and Cyclone Michaung in December 2023 over the Chennai region and Andhra Pradesh coast.

The same period also produced the Chennai floods of late 2015, when exceptionally heavy rain fell over the city in November and December. Events such as these show that the northeast monsoon can deliver both life-giving rain and destructive floods.

What Controls the Strength of the Northeast Monsoon?

The strength of the northeast monsoon is controlled mainly by the El Nino-Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD), and the relationships are opposite to those of the southwest monsoon. Research has repeatedly found that El Nino years tend to favour above-normal northeast monsoon rain over southern India, while La Nina years tend to favour a deficit.

• El Nino: Warm waters in the central Pacific encourage more convection over the equatorial Indian Ocean and favour rain over south-east India.
• La Nina: Cooler Pacific conditions are generally linked with weaker northeast monsoon rainfall in the south.
• Positive Indian Ocean Dipole: A warm western Indian Ocean and cool eastern Indian Ocean often support more rain over south India.
• Madden-Julian Oscillation: This eastward-moving pulse of cloud can boost rain when its active phase passes over the Bay of Bengal.
• Local sea temperatures: Warm water in the southern Bay of Bengal increases the moisture available to cyclones and depressions.

These links are tendencies and not rules. Individual seasons can behave differently when several influences compete, so the IMD issues its forecast for the northeast monsoon each autumn and revises it as the season develops.

How Is the Northeast Monsoon Different from the Southwest Monsoon?

The northeast monsoon differs from the southwest monsoon in its season, wind direction, rainfall amount and the regions it affects. The southwest monsoon brings roughly three-quarters of India’s rain to almost the entire country, while the northeast monsoon is a smaller, regional season focused on the south-east.

Why Does the Northeast Monsoon Matter for Tamil Nadu and the South?

The northeast monsoon matters for Tamil Nadu and the south because it refills reservoirs, tanks and aquifers that feed agriculture and cities for the rest of the year. Many parts of Tamil Nadu have no large snow-fed rivers, so local rain is the main source of surface water.

• Farming: Rain from October to December supports the samba and thaladi rice crops in the delta region, along with pulses, groundnut and millets in the drier districts.
• Urban water: Cities such as Chennai rely on lakes and reservoirs that fill primarily from northeast monsoon rain, so a failed season can lead to serious water shortages the following summer.
• Tank irrigation: Tamil Nadu has a long tradition of rain-fed irrigation tanks, which are filled during these months.
• Disaster risk: The same rain can cause flooding in low-lying and heavily built-up coastal areas when drains and river mouths are choked.
• Power and economy: Hydropower, fisheries and rural incomes in the south-east all respond to the season’s performance.

How Is Climate Change Affecting the Northeast Monsoon?

Climate change is expected to make northeast monsoon rainfall more intense and more variable, since a warmer Bay of Bengal supplies more moisture to cyclones and depressions. Observations have shown the northeast monsoon to be highly variable from year to year, and some studies suggest a rise in extreme rainfall events over southern India.

Warmer seas can also strengthen cyclones, and rapid intensification has been seen more often in recent years in the North Indian Ocean. At the same time, rapid urban growth along the east coast, with built-up areas covering lakes, marshes and floodplains, increases the damage caused by any given amount of rain.

Scientists caution that the relationship between warming and total seasonal rain in the northeast monsoon is still uncertain. What is clearer is that heavy single-day rainfall is likely to become a bigger concern, making flood forecasting, wetland protection and proper drainage planning essential for coastal cities.

Bottom Line

The northeast monsoon is India’s winter monsoon, a regional but vital rainy season that waters Tamil Nadu and the south-east coast from October to December. Driven by cold continental air flowing over the warm Bay of Bengal and punctuated by cyclones, it can bring both relief from drought and serious urban flooding.

Frequently Asked Questions

What is the northeast monsoon in simple terms?

The northeast monsoon is the October to December winter rainy season in southern India. Winds from the northeast cross the Bay of Bengal, pick up moisture and rain heavily on Tamil Nadu and nearby coastal regions.

Which states benefit most from the northeast monsoon?

Tamil Nadu benefits the most from the northeast monsoon, followed by Puducherry, coastal Andhra Pradesh, Rayalaseema, south interior Karnataka and parts of Kerala. Tamil Nadu receives close to half of its annual rainfall in this season.

Why does Tamil Nadu get more rain from the northeast monsoon than the southwest monsoon?

Tamil Nadu gets more rain from the northeast monsoon because the Western Ghats block most of the southwest monsoon, leaving the state in a rain shadow in summer. In winter the winds come from the Bay of Bengal side and rain falls on the east-facing coast.

When does the northeast monsoon begin in India?

The northeast monsoon normally begins around the third week of October over the south-east coast. The start usually follows the withdrawal of the southwest monsoon from the southern peninsula, and the season continues until about December.

Do cyclones form during the northeast monsoon?

Yes, the northeast monsoon season is also the main post-monsoon cyclone season for the Bay of Bengal. Cyclones and depressions between October and December bring heavy rain, strong winds and coastal flooding to Tamil Nadu, Andhra Pradesh and Odisha.

How does El Nino affect the northeast monsoon?

El Nino tends to increase northeast monsoon rainfall over southern India, which is the opposite of its usual effect on the southwest monsoon. The link is a tendency rather than a rule, and other factors such as the Indian Ocean Dipole also matter.

{“@context”:”https://schema.org”,”@graph”:[{“@type”:”FAQPage”,”mainEntity”:[{“@type”:”Question”,”name”:”What is the northeast monsoon in simple terms?”,”acceptedAnswer”:{“@type”:”Answer”,”text”:”The northeast monsoon is the October to December winter rainy season in southern India. Winds from the northeast cross the Bay of Bengal, pick up moisture and rain heavily on Tamil Nadu and nearby coastal regions.”}},{“@type”:”Question”,”name”:”Which states benefit most from the northeast monsoon?”,”acceptedAnswer”:{“@type”:”Answer”,”text”:”Tamil Nadu benefits the most from the northeast monsoon, followed by Puducherry, coastal Andhra Pradesh, Rayalaseema, south interior Karnataka and parts of Kerala. Tamil Nadu receives close to half of its annual rainfall in this season.”}},{“@type”:”Question”,”name”:”Why does Tamil Nadu get more rain from the northeast monsoon than the southwest monsoon?”,”acceptedAnswer”:{“@type”:”Answer”,”text”:”Tamil Nadu gets more rain from the northeast monsoon because the Western Ghats block most of the southwest monsoon, leaving the state in a rain shadow in summer. In winter the winds come from the Bay of Bengal side and rain falls on the east-facing coast.”}},{“@type”:”Question”,”name”:”When does the northeast monsoon begin in India?”,”acceptedAnswer”:{“@type”:”Answer”,”text”:”The northeast monsoon normally begins around the third week of October over the south-east coast. The start usually follows the withdrawal of the southwest monsoon from the southern peninsula, and the season continues until about December.”}},{“@type”:”Question”,”name”:”Do cyclones form during the northeast monsoon?”,”acceptedAnswer”:{“@type”:”Answer”,”text”:”Yes, the northeast monsoon season is also the main post-monsoon cyclone season for the Bay of Bengal. Cyclones and depressions between October and December bring heavy rain, strong winds and coastal flooding to Tamil Nadu, Andhra Pradesh and Odisha.”}},{“@type”:”Question”,”name”:”How does El Nino affect the northeast monsoon?”,”acceptedAnswer”:{“@type”:”Answer”,”text”:”El Nino tends to increase northeast monsoon rainfall over southern India, which is the opposite of its usual effect on the southwest monsoon. The link is a tendency rather than a rule, and other factors such as the Indian Ocean Dipole also matter.”}}]}]}