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[El Niño / La Niña]In August 2025, the sea surface temperature (SST) for the NINO.3 region was near normal with a deviation of -0.3°C, which is slightly lower than in July (Fig.3 and Table). The five-month running mean value of the NINO.3 SST deviation for June 2025 was -0.1°C. SSTs in the equatorial Pacific were above normal in the western part, while they were below normal mainly in the central 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 central and 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 in the central part. Convective activity over the equatorial Pacific was enhanced near the Maritime Continent but was weakened near the dateline (Fig.8, Fig.9 and Fig.10). Although these oceanic and atmospheric conditions partly resemble La Niña conditions, ENSO-neutral conditions persisted in August.
JMA's seasonal ensemble prediction system predicts that NINO.3 SST will decrease because of two factors: the growing cold subsurface water in the central and eastern equatorial Pacific; and persistence of 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 come closer to normal during the late boreal winter (Fig.11). In conclusion, La Niña-like conditions are likely to become clear toward the early boreal winter, but will not last long. Thus, it is more likely (60%) 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 August (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 August (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 .
