Island Climate Update 295 - May 2025

La Niña has now given way to ENSO-neutral conditions, and there is an 80% chance that ENSO-neutral conditions will continue during May-July 2025.

As of 21 April, the 30-day NINO3.4 Index (in the central equatorial Pacific) was -0.05˚C, in the neutral range. The 30-day relative Niño 3.4 Index (RONI) was -0.52˚C, reflective of the central equatorial Pacific being significantly cooler than the average of the global tropics.

The Southern Oscillation Index (SOI) was in the La Niña range during February-April (+1.0), while the April value was +0.9 (in the La Niña range).

The subsurface equatorial Pacific is up to 1˚C cooler than average just below the surface in the central part of the basin, a warming trend since last month. In addition, above average temperatures are emerging in the eastern Pacific, both indicating the decay of La Niña. However, above average upper oceanic heat content continues in western parts of the Pacific basin.

The South Pacific Convergence Zone (SPCZ) was located very close to its climatological normal position during April.

During May-July, model guidance continues to favour an enhancement in convective forcing over the western Pacific and Melanesia, collocated with the warmest sea surface temperatures and position of the SPCZ. This may lead to enhanced rainfall for island groups from southern Papua New Guinea east to Fiji. However, drier than normal conditions are likely to occur for many island groups along and north of the equator (see pages 6-7 for more information).

Tropical cyclone season officially ends on 30 April, although tropical cyclones can form outside of the official season.

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