Island Climate Update 276 - October 2023

El Niño has officially arrived. A majority of NIWA’s criteria for classifying an El Niño event were satisfied during September.

The monthly NINO3.4 Index anomaly (in the central equatorial Pacific) at the end of September was +1.58˚C, within the range of a strong El Niño (classified when the NINO3.4 Index is greater than 1.5˚C). The September 2023 NINO3.4 Index is exceeded only by 2015 and 1997, with data back to 1981. From an oceanic perspective, this strengthening El Niño ranks close to the most significant events in recent decades.

The Southern Oscillation Index (SOI) was within the El Niño range during September with a value of -1.3.

Trade wind strength was was below normal in the west-central Pacific just east of the International Date Line and near normal or above normal farther east during September, similar to August. During October, there is a stronger indication for a reduction in trades in the east-central Pacific. This will likely see conditions in the Niño 3 and 3.4 regions continue to warm.

In the sub-surface eastern equatorial Pacific Ocean, anomalies of +3˚C to +6˚C were occurring in the upper 100 metres in the east as of late September. The distribution of the anomalously warm water remained consistent with the development of an east-based canonical El Niño event. The abnormally warm waters are predicted to continue to surface and expand westward over the course of the next three to four months, with the event potentially peaking as a very strong El Niño (classified when the NINO3.4 Index is greater than 2.0˚C) in December 2023-January 2024.

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Island Climate Update - October 2023 [PDF 5.36 MB]