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The most recent IRI plume (pictured and discussed below) indicates El Niño is likely to form during the June-August 2023 season. It is expected to persist into the Northern Hemisphere winter. The combination of a forecasted third westerly wind event in mid-late May, and high levels of above-average oceanic heat content means that a potentially significant El Niño is on the horizon. While at least a weak El Niño is likely, the range of possibilities at the end of the year (November 2023-January 2024) includes an 80% chance of at least a moderate El Niño (Niño-3.4 ≥ 1.0°C) to about a 55% chance of a strong El Niño (Niño-3.4 ≥ 1.5°C). It also is possible that the tropical atmosphere does not couple with the ocean, and El Niño fails to materialize (5-10% chance).
In summary, a transition from ENSO-neutral is expected in the next couple of months. As the figure directly above indicates, there is a greater than 90% chance the El Niño will persist into the Northern Hemisphere winter.
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The key atmospheric variables currently indicate a developing El Niño. The traditional and equatorial Southern Oscillation Indices are in the El Niño range (as of May 16, 2023, the last observed value of the traditional Southern Oscillation Index was -7.1), and the low-level easterly winds have weakened in the central and western tropical Pacific. Upper-level wind anomalies remain westerly across the tropical Pacific, and near-normal cloudiness has been observed over the central and western Pacific Ocean. Since February 2023, there has been a significant increase in SSTs in the equatorial Pacific, particularly along the coast of South America (as of May 10, 2023, the SST anomaly in the Niño-1+2 region was +2.4 °C). This warming is due to warmer subsurface temperatures and a downwelling Kelvin wave, leading to the declaration of coastal El Niño conditions.
Per the IRI-ENSO plume, the forecasts indicate a high likelihood of El Niño. Specifically, during the boreal summer and autumn, the probabilities of El Niño range from 79% to 88%, as follows: June-August: 86%, July-September: 88%, August-October: 88%, September-November: 84%, and October-December: 79%. Thereafter, there is a slight decrease in the probability of El Niño during the upcoming boreal winter (November 2023-January 2024: 76%, December 2023-February 2024: 72%, and January-March 2024: 68%). The second most probable category throughout the forecast period is ENSO-neutral, with probabilities ranging from 12% to 29%. The redevelopment of La Niña is highly unlikely, with chances of less than 5%.
In summary, most of the models in the IRI ENSO-plume above now indicate the arrival of El Niño in June–August 2023. El Niño remains the dominant category during the rest of the forecast period (68-88% chance). We will continue to provide updates as the forecasts change.
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