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[El Niño / La Niña]In September 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 July 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 near the dateline. Convective activity over the equatorial Pacific was enhanced near the Maritime Continent but was suppressed near the 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 September.
The cold subsurface water volume continued in the central and eastern equatorial Pacific. JMA's seasonal ensemble prediction system predicts that NINO.3 SST will decrease due to the persistence of stronger-than-normal easterly winds over the equatorial Pacific toward the first half of 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 come closer to normal during the late boreal winter (Fig.11). In conclusion, La Niña-like conditions, though likely to continue toward the first half of boreal winter, will rapidly weaken in the second half, therefore it is more likely (80%) that ENSO-neutral conditions will persist until the late boreal winter.
[Western Pacific and Indian Ocean]
The area-averaged SST in the tropical western Pacific (NINO.WEST) region was above normal in September (Fig.3). The index is likely to be near or above normal until the late boreal winter (Fig.12).
The area-averaged SST in the tropical Indian Ocean (IOBW) region was below normal in September (Fig.3). The index is likely to be near or below normal until the late boreal winter (Fig.13).
The seasonal climate outlook for Japan is available here .
