Island Climate Update 308 - June 2026

ENSO situation summary

ENSO-neutral is currently in place in the tropical Pacific, but conditions are rapidly moving toward El Niño which is expected to form in the coming months. There is about a 90% chance for El Niño to form during June-August, with a 90% chance that El Niño will continue during July-September. The upcoming El Niño is expected to be strong, perhaps rivalling the strongest El Niños on record.

As of 10 May 2026, the 30-day NINO3.4 Index (in the central equatorial Pacific) was 0.75˚C, in the El Niño range. The 30-day relative Niño 3.4 Index (RONI) was 0.24˚C, in the neutral range and reflective of the central equatorial Pacific being warmer than the average of the global tropics.

The Southern Oscillation Index (SOI) was on the La Niña side of neutral during February-April 2026 (+0.4), while the April value was -0.7 (i.e. on the El Niño side of neutral).  

Subsurface ocean temperatures in the equatorial Pacific continue to be above average or well above average essentially everywhere across the basin.

Particularly warm water is located in the eastern and central equatorial Pacific between depths of about 50-150 metres, where temperature anomalies of 5-7°C are widespread. This continues to indicate the expectation for a strong El Niño to form in the coming 1-3 months.

During June-August, model guidance favours a continued chance of above normal or well above normal rainfall across most of Micronesia, several island groups along the equator, southern French Polynesia, and Pitcairn Islands. This may lead to enhanced rainfall for island groups such as Guam, the Northern Marianas, Federated States of Micronesia, the Marshall Islands, Nauru, and most of Kiribati.

Conversely, drier than normal or much drier than normal conditions are likely to occur for many island groups farther south, including Papua New Guinea east to Niue, and especially from Tuvalu east to the Marquesas (see pages 6-7 for more information).

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