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[El Niño / La Niña]In December 2025, the sea surface temperature (SST) for the NINO.3 region was below normal with a deviation of -0.6°C (Fig.3 and Table). The five-month running mean value of the NINO.3 SST deviation for October 2025 was -0.5°C. SSTs in the equatorial Pacific were above normal in the western part, while they were below normal from the central to eastern part (Fig.4 and Fig.6). Subsurface water temperatures in the equatorial Pacific were above normal in the western part, while they were below normal in the eastern part (Fig.5 and Fig.7). In the atmosphere, easterly winds in the lower troposphere (i.e., trade winds) over the equatorial Pacific were slightly stronger than normal in all regions. Convective activity was suppressed near the equatorial dateline (Fig.8, Fig.9 and Fig.10). Overall conditions in the atmosphere and ocean were similar to those of La Niña events, though ENSO-neutral conditions persisted in December.
The warm subsurface water in the western equatorial Pacific, extending towards the equatorial dateline, has begun propagating eastward in December. Associated with the eastward propagation, JMA's seasonal ensemble prediction system predicts that NINO.3 SST will rise, approaching near-normal by the end of winter and reaching near or above normal by the end of spring (Fig.11). In conclusion, the La Niña-like conditions will rapidly dissipate by the end of winter. Subsequently, while there is a possibility (40%) that El Niño conditions will develop by the end of spring, it is more likely (60%) that ENSO-neutral conditions will remain.
[Western Pacific and Indian Ocean]
The area-averaged SST in the tropical western Pacific (NINO.WEST) region was above normal in December (Fig.3). The index is likely to be above or near normal until the boreal spring (Fig.12).
The area-averaged SST in the tropical Indian Ocean (IOBW) region was below normal in December (Fig.3). The index is likely to be below or near normal until the boreal spring (Fig.13).
The seasonal climate outlook for Japan is available here .
