Global setting: December 2018

Over the past month, sea surface temperatures (SSTs) in the central Pacific (NINO3.4 Index, 5^oN-5^oS, 170^oW-120^oW) have remained above normal with anomalies currently exceeding +0.8^oC. This marks the fourth consecutive month SST anomalies in the central Pacific have exceeded 0.7^oC, which meets NIWA’S technical oceanic definition for El Niño. However, the coupling between the ocean and the atmosphere, necessary for the development of the ENSO (El Niño – Southern Oscillation) phenomenon, has not eventuated.   

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. If this coupling does not eventuate, then SST anomalies in the equatorial Pacific will have little relevance to the regional climate anomalies over and around New Zealand.

Sea Surface Temperatures

New Zealand’s coastal waters are currently much warmer than average for the time of year, with coastal SST anomalies exceeding +1^oC for all regions of New Zealand. Argo temperature profiles indicate that above normal subsurface temperatures around New Zealand have intensified during December 2018. Much warmer than normal ocean temperatures are also affecting large areas of the Tasman Sea. The dynamical models are consistent in predicting above to well above normal regional ocean temperatures during January – March 2019.