Island Climate Update 278 - December 2023
El Niño continued during November and will likely remain in place during the next three months. El Niño has around a 100% chance of persisting through February 2024.
The monthly NINO3.4 Index anomaly (in the central equatorial Pacific) at the end of November was +1.92˚C, well within the range of a strong El Niño (classified when the NINO3.4 Index is greater than 1.5˚C). The November 2023 NINO3.4 Index is exceeded only by 2015 and 1997, with data back to 1981. From an oceanic perspective, this El Niño continues to rank with the most significant events in recent decades.
The Southern Oscillation Index (SOI) was at the El Niño threshold from September-November (-1.0), and in the El Niño range during November (-1.1).
Trade wind strength was was below normal or well below normal in the Pacific during November, particularly just north of the equator and in the central and west. In parts of the region, this qualified as a Westerly Wind Burst (WWB). This WWB will be responsible for the eastward propagation of warm sea water along the equator through January. Another meaningful reduction or reversal in trade winds is possible during the second half of December.
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 November. Anomalies intensified at depth around the NINO3.4 region, resulting from a Westerly Wind Burst during the second half of November. Peak oceanic El Niño strength is most likely in January, but sustained peak intensity into February cannot be ruled out.
The associated abnormally warm water sitting near and north of both Vanuatu and Fiji may be a common genesis zone for tropical cyclone activity in the months ahead. A tropical cyclone is currently forming near the Solomon Islands, but it is not expected to impact any other island groups. An active pulse of the Madden-Julian Oscillation in mid-to-late December may generate additional tropical cyclone activity.