IMD forecasts below-normal October-December rain across most of India

The India Meteorological Department has forecast below-normal rainfall over most parts of India between October and December 2026, after declaring the rainy season over with a 13% southwest monsoon deficit. Parts of northwest India and the southern peninsula may get normal to above-normal rain. South Peninsular India is forecast at 88-112% of its 334.13 mm long period average. The IRI said the Nino 3.4 anomaly reached +3°C by mid-September.

Written by AI from Weather · not yet reviewed by an editor · Published 30 Sept 2026, 9:20 pm IST

Source

Weather · read the original report ↗

#el nino#imd#rainfall forecast#northeast monsoon#post-monsoon

Desk check · compared with the source

What the desk checked (5)

IMD forecasts below-normal rainfall over most of India during October-December 2026. — Attributed to IMD's latest probabilistic forecast in the source; described as most likely category, not a certainty.
The southwest monsoon ended with a 13% deficit. — Figure appears in source, attributed to IMD's declaration of the season's end.
South Peninsular India seasonal rainfall forecast normal, 88-112% of an LPA of 334.13 mm (1971-2020 baseline). — Figures appear in source and are attributed to IMD; internally consistent.
Nino 3.4 sea-surface temperature anomaly reached +3°C by mid-September, with all 22 models indicating very strong El Nino through winter. — Attributed to the September 2026 IRI assessment; not independently verifiable here.
Northeast monsoon accounts for about 30% of south Peninsular India's annual rainfall; Tamil Nadu and Puducherry get nearly half their annual rain then. — Stated in source without a named source for the climatological share.

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Analysts’ view opinion

AI Political Analyst

A rainfall outlook is no longer just a scientific bulletin — it is a document that shapes the political agenda. With the southwest monsoon ending 13% short and the IMD now forecasting below-normal rain for October-December, farm incomes, drinking water, power and food prices become a simultaneous test for both the Centre and the states. The forecast carries extra political weight in regions that depend on the northeast monsoon, such as Tamil Nadu and Puducherry.

The forecast of normal rainfall for south Peninsular India (88-112% of the Long Period Average) offers some relief to governments there, while the nationwide shortfall increases pressure on the Centre to show mitigation measures.
Periods of drought and water stress typically bring louder demands for disaster relief funds, compensation and loan waivers — a familiar flashpoint in Centre-state relations.
Advance warning cuts both ways politically: governments can claim preparedness, while opposition parties can ask why little was done despite an early signal.
Because the northeast monsoon supplies roughly 30% of south Peninsular India's annual rainfall, water management and reservoir sharing could resurface as an inter-state political issue.
The IMD outlook is probabilistic and regionally uneven, so even in an overall deficient season localised heavy spells could invite a very different line of criticism about flood preparedness.

What to watch — Watch whether states move early with water management plans, crop advisories and relief demands, and how the Centre responds to them.

The story establishes only the weather outlook; it does not tell us what any government will do, whether any relief or policy announcement has been made, or how this will affect electoral politics.

Deep dive

Research brief · 8 facts · 5 dates · exam-ready

The brief

Context

The India Meteorological Department (IMD) has declared the 2026 southwest monsoon season over, with rainfall ending 13% below normal, and has issued its probabilistic outlook for the October-December post-monsoon season. The outlook says most of India will see below-normal rainfall, with exceptions in parts of northwest India and the southern peninsula. The October-December period is the northeast monsoon season, which is the main rainfall season for south Peninsular India. The forecast comes as a sharply intensifying El Nino in the tropical Pacific — historically linked to weaker Indian rainfall — is expected to remain very strong into early 2027.

Key facts

IMD forecasts below-normal rainfall over most parts of India for October-December 2026.
The 2026 southwest monsoon ended with a 13% rainfall deficit, and IMD declared the rainy season over.
Parts of northwest India and southern parts of the peninsula are expected to get normal to above-normal rainfall.
South Peninsular India seasonal rainfall is forecast as normal, i.e. 88%-112% of its Long Period Average.
The October-December LPA for south Peninsular India is 334.13 mm, based on 1971-2020 rainfall data.
IMD uses the 1971-2020 baseline for its post-monsoon climatology.
The northeast monsoon accounts for roughly 30% of the annual rainfall of south Peninsular India; Tamil Nadu and Puducherry get nearly half their annual rain in the season.
The September 2026 IRI assessment found the Nino 3.4 sea-surface temperature anomaly had reached +3 degrees C by mid-September, with all 22 forecast models indicating very strong El Nino could persist through winter.

Timeline

Mid-September 2026Nino 3.4 sea-surface temperature anomaly reaches +3 degrees C, per IRI.
September 2026IRI assessment says the 2026 El Nino has intensified sharply and will stay very strong through year-end.
End of the 2026 southwest monsoon seasonIMD declares the rainy season over with a 13% monsoon deficit.
October-December 2026IMD probabilistic forecast period: below-normal rain over most of India; normal rain for south Peninsular India.
Through winter and into early 2027Very strong El Nino conditions expected to persist.

Who has a stake

India Meteorological Department (IMD) — Issues the probabilistic post-monsoon rainfall outlook and declares the monsoon's withdrawal; its accuracy guides public and official response.
Tamil Nadu and Puducherry — Receive nearly half their annual rainfall during the October-December northeast monsoon season, so the outlook directly affects them.
South Peninsular India — Depends on the northeast monsoon for about 30% of annual rainfall; forecast to be normal (88-112% of the 334.13 mm LPA).
International Research Institute for Climate and Society (IRI) — Provides the international El Nino assessment underpinning expectations of a very strong event into early 2027.
Northwest India and southern peninsular areas — Identified as exceptions likely to see normal to above-normal rainfall.
Residents across India — Face a drier-than-usual season overall, but with sharp regional variation and possible heavy rain spells from individual weather systems.

Why it matters

A deficient southwest monsoon followed by a below-normal October-December season compounds water stress, since the post-monsoon period is the principal rainfall season for southern India. Because the forecast is probabilistic, it signals the most likely category rather than ruling out rain, so individual systems can still bring heavy spells even in a dry season. The strengthening El Nino, projected to stay very strong into early 2027, makes the coming months a key test of preparedness.

UPSC angle

Prelims pointers

Southwest monsoon 2026 ended with a 13% deficit, as declared by IMD.
IMD's 'normal' rainfall category means 88%-112% of the Long Period Average (LPA).
October-December LPA for south Peninsular India: 334.13 mm, based on 1971-2020 data.
Northeast monsoon gives roughly 30% of south Peninsular India's annual rainfall; nearly half for Tamil Nadu and Puducherry.
Nino 3.4 SST anomaly hit +3 degrees C by mid-September 2026 (IRI); all 22 models saw very strong El Nino persisting through winter.
El Nino is a natural warming of the central and eastern tropical Pacific, historically linked to weaker Indian monsoon rainfall.

Mains framing

The IMD's October-December 2026 outlook of below-normal rainfall over most of India, following a southwest monsoon that ended 13% deficient, illustrates how a single deficient year can be compounded by a weak post-monsoon season. The immediate driver cited is a rapidly strengthening El Nino, with the Nino 3.4 anomaly at +3 degrees C by mid-September 2026 and all 22 IRI forecast models pointing to very strong conditions through winter; El Nino has historically been associated with weaker Indian rainfall, though the source notes Indian rainfall is also shaped by several other oceanic and atmospheric factors. The implications are sharpest for south Peninsular India, where the northeast monsoon supplies about 30% of annual rainfall and nearly half of Tamil Nadu's and Puducherry's — though this region is forecast to be normal, at 88-112% of the 334.13 mm LPA, with some southern and northwest areas possibly above normal. The way forward lies in reading the forecast as probabilistic rather than deterministic: it identifies the most likely rainfall category, leaves areas with no clear model signal, and does not preclude heavy rain from individual weather systems, so planning must be region-specific and prepared for both deficit and localised excess.

Key terms

Long Period Average (LPA): The long-term average rainfall baseline against which a season is judged; IMD uses 1971-2020 data, with 334.13 mm as the October-December LPA for south Peninsular India.
Northeast monsoon: The October-December rainfall season that provides roughly 30% of south Peninsular India's annual rain and nearly half of Tamil Nadu's and Puducherry's.
El Nino: A natural warming of the central and eastern tropical Pacific that alters weather worldwide and is historically linked to weaker Indian monsoon rainfall.
Nino 3.4 anomaly: The sea-surface temperature departure in a central Pacific region used to gauge El Nino strength; it reached +3 degrees C by mid-September 2026.
Probabilistic forecast: A forecast that identifies the most likely rainfall category rather than asserting rain will or will not occur, and may show no clear signal in some areas.
IRI: International Research Institute for Climate and Society, which issued the September 2026 assessment on the intensifying El Nino.

Practice questions

Examine how El Nino influences Indian rainfall, and why a strong El Nino does not automatically translate into uniform rainfall deficits across the country.
Discuss the significance of the northeast monsoon for south Peninsular India and the consequences of a below-normal October-December season.
What is a probabilistic rainfall forecast, and how should administrations use such outlooks for water and disaster management?

Grounded only in the source report — figures and dates are the source's, not inferred.

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