Island Climate Update 251 - August 2021

The NINO3.4 Index anomaly (in the central Pacific) during July was 0.08 ̊C. The Southern Oscillation Index was +1.7, firmly in La Niña territory.

During July, upper-oceanic heat content continued to decrease across the equatorial Pacific, a trend that started in June. Cooler waters at depth progressed toward the surface and warmer conditions close to the surface contracted and became less anomalous. Trade winds were enhanced around the equatorial Pacific, consistent with an atmosphere that was trending in a La Niña-like direction. This is expected to continue, with enhanced trade winds expected from mid-August. In terms of rainfall, island groups nearest to the equator will likely experience drier than normal conditions.

A negative Indian Ocean Dipole (IOD) event was classified by the Australian Bureau of Meteorology during July, referring to well above average SSTs in the tropical eastern Indian Ocean. An Atlantic Niño, characterised by warmer than average ocean temperatures in the central and eastern equatorial Atlantic, persisted also throughout the month. These teleconnections, or climate patterns related to one another across long distances, also support an ocean-atmosphere system that is likely to conEnue to trend in a La Niña-like direction.

On the balance of evidence, the re-emergence of La Niña or continuation of ENSO “cool” neutral conditions are about equally likely (45-55% chance each) over the coming three to six months. NIWA has therefore activated a La Niña watch. Regardless of ENSO status, the climate system will likely lean in a La Niña-like direction through the end of the year.

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Download the full report: Island Climate Update - August 2021