The El Niño phenomenon is a periodic warming phenomenon in the tropical Pacific Ocean that leads to a rise in global temperature and suppression of monsoon activity in India. Last week, the Climatic Prediction Center (CPC) of the US National Oceanic and Atmospheric Administration (NOAA) published its monthly forecast of El Niño’s development over the rest of the year. Forecasts indicate that the probability of a strong El Niño event this year is now higher than previously expected. What does this mean for the monsoon this year?
The relationship between forecasts for a strong El Niño and the monsoon for 2026 requires a detailed look at both the forecast and how El Niño relates to the monsoon. The first thing the forecast shows is that El Niño is now more likely to arrive earlier in the May-July season (forecast for three-month seasons), compared to the expected arrival in June-August. This can be seen in the fact that the probability of El Niño occurring in May and July rose from 45% in the March forecast to 61% in the April forecast.
The second thing the forecast shows is that it is somewhat likely that El Niño will be of at least moderate intensity by the July-September season, with a 49% probability. This becomes quite possible by August and October, when the probability of a moderate El Niño event is at least 63%. On the other hand, the probability of a strong El Niño occurring is only 50% in the October-December season.
In summary, forecasts indicate that El Niño is very likely to affect all monsoon months, which run from June to September. However, its strength is likely to be moderate only in the second half of the monsoon season, and strong only after the monsoon ends. This must certainly be read in conjunction with the fact that every new forecast in recent months has shown that El Niño is stronger than previous forecasts.
How will El Niño affect the monsoon? El Niño conditions are said to prevail if the mean El Niño 3.4 sea surface temperature anomaly — which is the deviation of sea surface temperatures in the El Niño 3.4 region from the 30-year average that is updated every five years — is at least 0.5. Moderate El Niño conditions are said to exist if this anomaly is in the range of 1-1.5; Strong and very strong El Niño conditions are said to be present if the number exceeds 1.5 and 2, respectively.
Historical data show that if all four months of the monsoon are affected by El Niño, a deficit in monsoon rainfall is almost guaranteed. Sixteen of the 20 seasons affected by El Niño since 1951 have had deficient monsoon rains: a probability of 80%.
The chances of a deficit falling outside the normal range by 4% are certainly lower: only 55%. However, this statistic lends credence to the Indian Meteorological Department (IMD) forecast of less than normal rainfall during this monsoon. Historical data also show that the strength of El Niño or the number of months affected by it are not closely related to the performance of the monsoon. This is expected because El Niño, although an important factor in monsoon performance, is not the only factor affecting monsoon performance.
Another thing to note while reading the relationship between El Niño and monsoon performance is that the relationship is not the same across the country, nor has it been constant over the years. As HT noted in a September 2024 article — using 2023 research published in Nature by KS Athira and others — the monsoon’s connection to conditions in the tropical Pacific is becoming weaker. This is largely due to central India, while the relationship has increased and remained constant in northern and southern India, respectively.
Therefore, one can expect there to be a deficit in this monsoon based on El Niño forecasts alone. After taking into account expectations of other factors, the IMD forecasts a deficit of 8% with an error range of +/-5%. However, a better picture will only emerge in the late May and early June forecasts, which have shown slightly better accuracy than the IMD’s first monsoon forecasts in the past.
