Island Climate Update 255 - December 2021

The NINO3.4 Index anomaly (in the central Pacific) during November (through the 28th) was -0.59˚C and the Southern Oscillation Index (SOI) was +1.1, both near the La Niña threshold. The three month average SOI was +0.9.

Upper-oceanic heat content was well below normal in the central and eastern equatorial Pacific during November as a full-basin La Niña signature matured. Modest cool anomalies persisted in the sub-surface, although the coolest water relative to normal has now surfaced or is surfacing. From an oceanic perspective, La Niña will likely peak over the next month.

Trade winds across the central Pacific were enhanced along the equator during November, particularly near and west of the International Date Line. Based on the trends described above, NIWA has classified a La Niña event, with an 85% chance of it continuing through February. Between March-May 2022, there is a 65% chance for the reemergence of ENSO neutral conditions.

The active phase of the Madden-Julian Oscillation (MJO) was over the western Pacific at the beginning of December. This can help to facilitate a more favourable state for tropical cyclone development. As the MJO continues to move across the Pacific during mid-to-late December, island groups, particularly in the western part of the basin such as New Caledonia and Vanuatu, should remain aware of an increased risk for regional tropical cyclone activity.

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Download the full report: Island Climate Update December 2021.

Preview the new ICU bulletin: https://niwa.co.nz/sites/niwa.co.nz/files/ICU-revision-Dec-2021.pdf