Island Climate Update 270 - April 2023

The monthly NINO3.4 Index anomaly (in the central equatorial Pacific) at the end of March was -0.01˚C, in the neutral range for the second consecutive month.

The SOI was neutral (0.0) during March and +0.6 from January-March, suggestive of a trend away from La Niña-like atmospheric patterns.

Trade wind strength was significantly reduced across the equatorial Pacific during March, owing to a westerly wind burst (WWB) during the first 10 days of the month. WWB’s are a critical mechanism toward developing El Niño events.

The trade wind reduction was largest in the eastern part of the basin, which is also where the most substantial ocean warming took place. April shows a continued reduction in trade wind strength, particularly in the west-central part of the basin, which will likely lead to the eastward movement of warm water – an El Niño-like trend.

In the sub-surface equatorial Pacific, dramatic warming occurred during March, with widespread anomalies of 3˚C to 5˚C above average. In the central part of the basin, a downwelling oceanic Kelvin Wave was associated with a large, eastward-progressing area of warmer than average seas. This feature may reach the eastern Pacific and move toward the ocean’s surface during the next two months. These features also suggest that the sub-surface ocean is exhibiting a strong trend toward an El Niño event.

NIWA’s analysis indicates that ENSO-neutral conditions have an 80% chance of continuing through June. Thereafter, El Niño has a 65-70% chance of developing. The changes observed during March, as described above, support a continued progression toward El Niño thresholds. NIWA’s ENSO criteria supports a move to El Niño Watch.

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Island Climate Update April 2023 [PDF 5.7 MB]