Indian Ocean Dipole (IOD), the Indian Ocean counterpart of the El Niño–La Niña phenomena in the equatorial Pacific Ocean, could prove to be the decisive variable in determining how the rapidly evolving ‘strong to very strong’ El Niño influences India’s June–September south-west monsoon rainfall.

Warming of ocean 

Sea-surface temperatures in the Niño 3.4 region of the tropical Pacific, a key indicator for the El Niño–Southern Oscillation, are rising rapidly, already 2–3°C above the 1981–2010 average.

Forecasters point to the possible development of a ‘Super El Niño,’ comparable to strong events in 1982, 1997 and 2015. But 1997 had delivered a normal monsoon, indicating a tenuous one-to-one correlation.

May form by August

There is an 80 per cent chance of a strong El Niño forming by August, potentially making it one of the most intense in over a century. Such conditions are typically associated with droughts in parts of Asia and heavy rainfall in the Americas.

“There is going to be a strong event, whether you call it ‘super’ or ‘Godzilla’”, says GP Sharma AVM, President, Meteorology and Climate Change at Skymet. The private forecaster’s long-range forecast released on Tuesday projects the monsoon taking a hit from the El Niño with seasonal rainfall likely at 94 per cent of the long-term average (LPA), indicating a below-normal season this year.

Multiple factors

The evolving situation is similar to 2014–15, when a strong El Niño contributed to drought conditions in India. However, Sharma notes that the monsoon is influenced by multiple factors, not just the strength of El Niño alone.

He cites the alternating positive or negative phases of the IOD as one. A positive IOD can support the monsoon, as seen in 2019 when it helped revive rainfall in the latter half of the season and drive it up to a surplus. However, the Indian Ocean operates independently of the Pacific, and its behaviour can vary.

Impact on monsoon

El Niño is often associated with a neutral or positive IOD. But if a negative IOD coincides with El Niño, it can significantly weaken the monsoon.

Conversely, during La Niña years, a negative IOD is more common, though La Niña can offset some of its adverse effects.

By the same token, a positive IOD, if it develops this year, could partly offset the impact of El Niño, though the benefits may be uneven and largely confined to southern and central parts of the country. 

Accuracy of forecasts

“The difficulty with the IOD is that it cannot be forecast with precision until the final weeks; unlike El Niño or La Niña, which can be anticipated months in advance,” said Sharma.

“When it does turn positive, its influence is felt largely over the southern peninsula, as warming in the adjoining Arabian Sea and the western Indian Ocean enhances convection, promotes cloud formation and, in turn, supports rainfall.”

Published on April 8, 2026