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[El Niño / La Niña]In October 2025, the sea surface temperature (SST) for the NINO.3 region was below normal with a deviation of -0.5°C (Fig.3 and Table). The five-month running mean value of the NINO.3 SST deviation for August 2025 was -0.3°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 from the central to 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 stronger than normal from the western to central part. Convective activity was enhanced near the Maritime Continent but 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 October.
The cold subsurface water volume persisted in the central and eastern equatorial Pacific. JMA's seasonal ensemble prediction system predicts that NINO.3 SST will remain below normal due to stronger-than-normal easterly winds over the equatorial Pacific toward the early boreal winter. However, the La Niña-like conditions will not last long due to atmosphere-ocean coupling expected to weaken afterwards, and it is predicted that NINO.3 SST will be near normal by the early boreal spring (Fig.11). In conclusion, La Niña-like conditions, though likely to continue toward the early boreal winter, will rapidly weaken later in the winter. Therefore, it is more likely (80%) that ENSO-neutral conditions will persist until the early boreal spring.
[Western Pacific and Indian Ocean]
The area-averaged SST in the tropical western Pacific (NINO.WEST) region was above normal in October (Fig.3). The index is likely to be near or above normal until the early boreal spring (Fig.12).
The area-averaged SST in the tropical Indian Ocean (IOBW) region was below normal in October (Fig.3). The index is likely to be below normal until the early boreal spring (Fig.13).
The seasonal climate outlook for Japan is available here .
