India's 2026 southwest monsoon ended 12.6% below normal, the weakest season since 2015. Behind the shortfall is a warming of the equatorial Pacific Ocean, thousands of kilometres away, and an Indian Ocean pattern that came too late to help this time.
El Nino is the warm phase of a natural climate cycle in the tropical Pacific. Every few years, surface waters in the central and eastern Pacific become unusually warm, and that changes where the heaviest rain-bearing clouds form. For India, the shift usually means a weaker monsoon.
Scientists track it through the Nino-3.4 region, a band of the central equatorial Pacific. On October 8, sea-surface temperatures there were 2.1°C above normal — in the "strong" El Nino range, according to the US Climate Prediction Center’s (CPC) ENSO Diagnostic Discussion of October 8, 2026.
NOAA’s Climate Prediction Center puts the odds at 83% that El Nino reaches "historic" strength — a three-month sea-surface-temperature anomaly of 2.5°C or more, stronger than any event since 1950 — for the October-December 2026 window. The chances are 54% for September-November and 70% for November-January, reflecting an event expected to peak around the turn of the year.
The World Meteorological Organization goes further: in a September 3, 2026 update, it put the likelihood of El Nino persisting through February 2027 — covering the whole rabi growing season — at "exceptionally high... nearly 100%", the most unequivocal such forecast in its history.
A strong El Nino does not guarantee a failed monsoon. In 1997, during one of the strongest El Nino events on record, a positive Indian Ocean Dipole (IOD) helped keep India's monsoon rainfall close to normal. In a positive IOD, the western Indian Ocean runs warmer than the eastern side.
This year the IOD arrived too late in the season to provide the same cushion.
India received 759.4mm of rain over the monsoon season, against a normal of 868.6mm — a shortfall of 12.6%. Seventeen of the country's 36 meteorological subdivisions ended the season with deficient rainfall.
The regional split was sharp. According to IMD’s own “Salient Features of the 2026 Southwest Monsoon Season” report (September 30, 2026), East and northeast India received just 74% of its long-period average rainfall (a 26% deficit) and the south peninsula 76% (24% short) — both in the “deficient” band — while northwest India (94% of LPA, 6% short) and central India (97% of LPA, 3% short) stayed in the normal range. Of the country’s 36 meteorological subdivisions, 17 (42% of the area) ended deficient, 18 (53% of the area) were normal, and one — Odisha — recorded excess rainfall.
The effects can now be seen in falling reservoir levels and in drought declarations across Karnataka, Maharashtra, Andhra Pradesh and Telangana.