In May, weak El Niño conditions emerged as above-average sea surface temperatures (SSTs) strengthened across the equatorial Pacific Ocean [Fig. 1]. All of the latest weekly Niño indices were more than +0.5°C: Niño-3.4 was +0.8°C, Niño-3 was +1.1°C, and Niño1+2 was +2.3°C [Fig. 2]. Area-averaged subsurface temperatures anomalies remained positive [Fig. 3], reflecting the continuation of widespread anomalous warmth below the surface of the equatorial Pacific Ocean [Fig. 4]. For the May average, low-level wind anomalies were westerly over the western equatorial Pacific Ocean, while upper-level wind anomalies were westerly over the eastern Pacific Ocean. Convection was enhanced along the equator and was suppressed over Indonesia [Fig. 5]. Both the equatorial SOI and traditional SOI were significantly negative. Collectively, the coupled ocean-atmosphere system reflected the emergence of El Niño conditions.

The most recent IRI plume indicates the continuation of El Niño through the Northern Hemisphere winter 2023-24 [Fig. 6]. Confidence in the occurrence of El Niño increases into the fall, reflecting the expectation that seasonally averaged Niño-3.4 index values will continue to increase. Another downwelling Kelvin wave is emerging in the western Pacific Ocean, and westerly wind anomalies are forecasted to recur over the western Pacific. At its peak, the chance of a strong El Niño is nearly the same as it was last month (56% chance of November-January Niño-3.4 ≥ 1.5°C), with an 84% chance of exceeding moderate strength (Niño-3.4 ≥ 1.0°C). In summary, El Niño conditions are present and are expected to gradually strengthen into the Northern Hemisphere winter 2023-24 [Fig. 7].