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[El Niño / La Niña]In October 2024, the sea surface temperature (SST) for the NINO.3 region was near normal with a deviation of -0.4°C (Fig.3 and Table). The five-month running mean value of the NINO.3 SST deviation for August 2024 was -0.3°C. SSTs in the equatorial Pacific were above normal in the western part and 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, and the cold subsurface water volume increased in the eastern part as well (Fig.5 and Fig.7). In the atmosphere, convective activity near the dateline over the equatorial Pacific was less active than normal, and easterly winds in the lower troposphere (i.e., trade winds) over the central equatorial Pacific were stronger than normal, partly due to the tropical intraseasonal oscillation (Fig.8, Fig.9 and Fig.10). These oceanic and atmospheric conditions in the equatorial Pacific comprehensively indicate that ENSO-neutral conditions persisted in October. Overall conditions in the atmosphere and ocean, however, indicate that common features of past La Niña events were becoming clear.
The cold subsurface water volume increased from the central to eastern equatorial Pacific (Fig.5). JMA's seasonal ensemble prediction system predicts that trade winds over the western to central equatorial Pacific will be stronger than normal and the cold subsurface water volume from the central to eastern equatorial Pacific will increase further and propagate eastward. As a result, it is expected that NINO.3 SST will be below normal by boreal winter. However, the conditions will not last until spring and NINO.3 SST is predicted to come closer to normal towards the coming spring as the atmosphere-ocean coupling weakens (Fig.11). In conclusion, the characteristics of La Niña conditions will become clearer towards and during winter, but the conditions will not last until spring, thus, it is more likely that ENSO-neutral conditions will continue (60 %) than the definition of a La Niña event will be met (40 %).
[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 above or near normal until boreal spring (Fig.12).
The area-averaged SST in the tropical Indian Ocean (IOBW) region was above normal in October (Fig.3). It is expected that the index will approach the normal towards the coming winter and be near or below normal in boreal spring (Fig.13).
The seasonal climate outlook for Japan is available here .
