During September, the NINO3.4 Index anomaly (central Pacific) was 0.71˚C. The NINO 1+2 Index (eastern Pacific) was 0.76 C. Upper oceanic heat content remained lower than normal with continued decreases observed in the east central part of the Pacific basin since August. Heat content continued to be higher than normal in the western Pacific. Overall, the pattern is consistent with La Niña conditions.
Trade winds during September continued to be stronger than normal across the equatorial Pacific, particularly near and west of the International Dateline. This contributed to additional upwelling, which led to continued cooling sea surface temperatures. This pattern is expected to continue into October and November, with enhanced trade winds focusing on the central Pacific (e.g. Kiribati, Nauru) this may mean that the coolest ocean temperatures, with respect to average, migrate westward in time.
Rainfall and convection continued to be below normal in the central equatorial Pacific (Nauru, Kiribati, Tuvalu) during September. This was surrounded by isolated areas of above normal rainfall to the north, south and west, including a more active than normal South Pacific Convergence Zone, particularly to the west of the International Dateline. The pattern was La Niña like in nature, although the atmosphere has yet to fully couple to the ocean with some variability continuing.
Based on the consensus from international models, the probability for La Niña conditions is 77% for the October December period, a large increase of 20% from last month. For the January March 2021 period, the probability for La Niña is 51% and 46% for ENSO neutral conditions.
Based on the observations and forecast guidance, a La Niña Alert continues this month.
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Download the full report: Island Climate Update - October 2020
