Island Climate Update 243 - December 2020

During November, the NINO3.4 Index anomaly (central Pacific) was 1.02˚C. The NINO 1+2 Index (eastern Pacific) was 0.54 C. The most unusually cool SSTs have now shifted into the central Pacific.

While the pattern is consistent with La Niña, its flavour may be more of the central Pacific ( i.e. Modoki ) variety. Upper oceanic heat content continued to decrease in the east central part of the Pacific basin. Meanwhile, the western Pacific warm pool, a signature of La Niña, intensified.

Trade winds during November were enhanced across the west central equatorial Pacific ( e.g. Nauru, Kiribati), but were closer to normal in the east. This contributed to additional cooling of SSTs in the NINO3.4 region. Trade winds are expected to remain strong into January, with La Niña conditions likely peaking in early 2021.

Rainfall and convection were well below normal in the west central equatorial Pacific for the second consecutive month, aligned with La Niña. The South Pacific Convergence Zone was again displaced to the south during November. Above normal rainfall also occurred in countries north of the Equator, a hallmark of canonical La Niña conditions. For high islands, the potential for landslides and river flooding is higher than normal this coming wet season in the off equatorial South Pacific (New Caledonia, Vanuatu, Fiji, Samoa and southern Cook Islands), especially when a tropical disturbance follows a prolonged period of wetter than normal conditions.

Based on the consensus from international models, the probability for La Niña conditions is 97% for the December - February 2021 period. For the March - May 2021 period, the probability for La Niña is 57% and 42% for ENSO neutral conditions.

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