Island Climate Update 254 - November 2021

The NINO3.4 Index anomaly (in the central Pacific) during October was -0.59˚C. The latest weekly value was -0.80˚C, continuing the trend towards La Niña. The Southern Oscillation Index (SOI) was +0.7 during October and August-October, on the La Niña side of neutral. Overall, this represented an ocean-atmosphere system that was on the verge of La Niña conditions. 

During October, upper-oceanic heat content decreased substantially across the equatorial Pacific. Sub-surface ocean conditions during the month were 3˚C to 4˚C colder than average around 100 m depth in the east-central Pacific, a marked trend from September.

Trade winds were again stronger than normal across the equatorial Pacific during October and are expected to remain enhanced through November. The influence of these enhanced trade winds will result in continued cooling of the sea surface.

Based on the trends described above, NIWA has moved to La Niña Alert. There is an 80% chance for the development of a La Niña event between November 2021 -January 2022 based on international guidance. 

Over the last 90 days and generally consistent with La Niña-like conditions, parts of several island groups have experienced very low rainfall (≤10th percentile), including the Northern Marianas, FSM, Nauru, Kiribati, Wallis & Futuna, northern Fiji, northern Tonga, Pitcairn Islands, and parts of French Polynesia.

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Download the full report: Island Climate Update November 2021