Island Climate Update 220 - January 2019
Over the past month, sea surface temperatures (SSTs) in the central Pacific have remained above normal with the NINO3.4 index anomalies currently exceeding +0.8°C. This marks the fourth consecutive month SST anomalies in the central Pacific have exceeded 0.7°C, which meets the technical oceanicdefinition for El Niño.
Warmer than average subsurface ocean waters persisted in the month of December 2018. The integrated heat content anomalies (over the top 300m of the ocean) in the equatorial Pacific are slightly weaker than they were at the beginning of November 2018, with anomalies exceeding 1.5°C now restricted to the eastern Pacific between 130oW and 115oW.
The coupling between the ocean and the atmosphere, necessary for the development of the ENSO (El Niño – Southern Oscillation) phenomenon, has not eventuated. Almost all atmospheric indicators are well under the conventional El Niño thresholds. The latest Southern Oscillation Index (SOI) is currently (December 2018) positivewith a value of +0.8 (i.e., close to La Niña conventional thresholds). The trade winds have been slightly weaker than normal (westerly anomalies) but not persistently so, and the convection and rainfall anomaly patterns are inconsistent with a traditional El Niño, with enhanced convective activity and rainfall in the western Pacific.
The consensus from international models is for weak to moderate oceanic El Niño conditions to persist over next three-month period (96% chance over January – March 2019), but it is unclear whether the atmosphere will eventually catch up with the ocean and lead to a fully coupled El Niño – Southern Oscillation (ENSO) phenomenon.