Island Climate Update 272 - June 2023

The monthly NINO3.4 Index anomaly (in the central equatorial Pacific) at the end of May was 0.49˚C, an increase of nearly 0.3˚C from April and trending toward NIWA’s El Niño threshold of 0.7˚C.

The SOI was negative (-1.7) during May, the lowest value since January 2016 (during the last major El Niño event). This suggests that the atmosphere was beginning to respond to the warming seas.

May trade winds were close to normal in the central equatorial Pacific, but a relaxation of trades in early and late June will enable further warming of sea surface temperatures.

In the sub-surface equatorial Pacific, the most unusually warm water consolidated in the east with anomalies reaching in excess of 4˚C. In the central part of the basin, anomalies of 2-4˚C were common. Pulses of the Madden-Julian Oscillation (MJO) during the month and season ahead will allow the warm water to migrate toward the surface. It should be noted that the persistence of warmth in the West Pacific Warm Pool may allow La Niña-like patterns to occur from time-to-time over the next month or two, lengthening the transition window from La Niña toward El Niño.

NIWA’s analysis indicates that oceanic and atmospheric indicators have trended closer to El Niño thresholds. For now, NIWA remains at El Niño Watch. However, key indicators point to a transition to El Niño “Alert” around August and then an event shortly thereafter.

Overall, El Niño has a 90% chance of developing by the August-October period with air and sea temperatures, rainfall, and sea level anomalies tending in an El Niño like direction during the season ahead.

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