Weather Bee: What do strong El Niño forecasts mean for the 2026 monsoon?

EL Niño is a cyclical warming of the equatorial pacific sea Ocean that warms the domain and suppresses monsoon activity in republic of india. Endure week, the Climate Prediction Center (CPC) of the National Oceanic and Atmospheric Administration (NOAA) of the United States published its monthly forecast on the development of El Niño through the rest of the year. The forecast suggests that the probability of a strong El Niño this year is higher now than previously believed. What does this mean for the monsoon this year?The relation between the forecast for a strong El Niño and the 2026 monsoon 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 likely to arrive as early as the May–July season (the forecast is for three-month seasons), compared to the June–August arrival expected earlier. This can be seen in the fact that the probability of an El Niño developing in May–July has increased 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 likely by August–October, when the probability of at least a moderate El Niño is 63%. The probability of a strong El Niño, on the other hand, reaches 50% only in the October–December season. In summary, the forecasts mean that it is very likely that El Niño will affect all months of the monsoon, which runs from June to September. However, its strength is likely to be only moderate in the second half of the monsoon season, and strong only after the monsoon is over. To be sure, this must be read alongside the fact that each new forecast in recent months has shown El Niño becoming stronger than in preceding forecasts.How will El Niño affect the monsoon? El Niño conditions are said to prevail if the average Niño 3.4 SST anomaly—this is the deviation of sea surface temperatures in the Niño 3.4 region from a 30-year average updated every five years—is at least 0.5. Moderate El Niño conditions are said to be in place if this anomaly is in the 1–1.5 range; and strong and very strong El Niño conditions are said to be in place if the number goes above 1.5 and 2 respectively.Historical data shows that if all four months of the monsoon are affected by an El Niño, a deficit in monsoon rainfall is almost guaranteed. Sixteen of the 20 monsoons affected by El Niño since 1951 have had a deficit in monsoon rains: an 80% probability.To be sure, the probability of the deficit being outside the normal range of 4% deficit is lower: only 55%. Nonetheless, this statistic lends credence to the India Meteorological Department (IMD) modelled forecast of below-normal rains this monsoon. Historical data also shows that the strength of El Niño or the number of months affected by it are not strongly correlated with monsoon performance. This is expected because El Niño, while being an important factor in monsoon performance, is not the only factor that affects monsoon performance. Another thing to note while reading the relation between El Niño and monsoon performance is that the relation is neither the same for all parts of the country, nor has it been steady over the years. As HT pointed out in a September 2024 story – using a 2023 paper published in Nature by K S Athira and others – monsoon’s correlation with the conditions in the equatorial Pacific Ocean have become weaker. This is largely because of central India, while the relation has increased and held steady in northern and southern India, respectively.Therefore, one can expect this monsoon to have a deficit purely on the basis of the El Niño forecast. After taking into account the forecast for other factors, the IMD has predicted a deficit of 8% with an error range of +/-5%. However, a better picture will emerge only in the late May/early June forecast, which has shown marginally better accuracy than IMD’s first monsoon forecast in the past.