El Niño continued during December and has around a 100% chance of persisting through March.
The monthly NINO3.4 Index anomaly (in the central equatorial Pacific) at the end of December was +2.01˚C, within the range of a very strong El Niño (classified when the NINO3.4 Index is greater than 2.0˚C). The December 2023 NINO3.4 Index was exceeded by 2015, 1997, and 1982 with data back to 1981. From an oceanic perspective, this El Niño ranks with the most significant events in recent decades.
The Southern Oscillation Index (SOI) was in the neutral range during December (-0.4) and on the El Niño side of neutral during October-December (-0.6). This implies that El Niño’s reflection in the atmosphere, via pressure and circulation patterns, has been atypical.
Trade wind strength was below or well below normal in the central and west-central equatorial Pacific during December. Trade wind strength is forecast to gradually increase during January. Based on this, it’s likely that the El Niño event is near peak intensity as of early January.
In the sub-surface central and eastern equatorial Pacific Ocean, anomalies of +3˚C to +6˚C were occurring in the upper 100 metres as of late December. Anomalies of +2˚C persisted near the International Dateline, giving the El Niño more of a “full-basin” appearance rather than a classical, east-based event.
In the sub-surface western equatorial Pacific, waters were 1 to 3˚C cooler than average, signalling a shifting oceanic state and one that is favoured to return to neutral conditions between April-June as this cooler water gradually pushes eastward.
A marine heatwave is active between northern Vanuatu and Fiji, extending eastward to near Samoa and westward toward Papua New Guinea. While tropical cyclone activity looks unlikely during early-to-mid January, a pulse of the Madden-Julian Oscillation during late January into February may trigger development. All islands should remain vigilant, as tropical cyclone season continues through April.
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Island Climate Update - January 2024 [PDF 6MB]
