Global setting: January 2018

Weak La Niña conditions continued in the tropical Pacific during January 2018. Below average sea surface temperatures (SSTs) remained present in the central and eastern equatorial Pacific Ocean but warmed slightly compared to December 2017.

The consensus from international models is that weak La Niña conditions (50% chance) are as likely as ENSO neutral conditions (50% chance) over the next 3 months (February – April 2018). The chance for ENSO neutral conditions then increases during the May – July 2018 period (65% chance). Overall, this suggests that a continued decay of La Niña conditions is expected over the next three months.

Apart from waning La Niña conditions, New Zealand’s regional climate over the next three month period is expected to be dominated by the very warm ocean waters (so called “marine heatwave”) present around the country, in the Tasman Sea, and in the Southwest Pacific Ocean.

For February – April 2018, the atmospheric circulation around New Zealand is forecast to be characterized by higher pressures than normal east and south of the country, while lower pressure than normal is forecast over the Tasman Sea, extending over the North Island. This pressure pattern, in concert with the marine heatwave, is expected to be associated with warmer than average air temperatures, occasional significant rainfall events, and flow anomalies from the northeasterly quarter.

Sea Surface Temperatures

Coastal waters remain much warmer than average all around New Zealand, in the Tasman Sea, and in the Southwest Pacific with anomalies currently exceeding +2.0oC for all coastal areas around the country. Toward the end of January 2018, the so called “marine heatwave” reached a secondary anomalous peak (the first peak occurred in early December).

According to the dynamical models’ forecasts, significantly warmer than average SSTs are likely to persist for at least part of the next 3 months (February – April 2018), although the anomalies are expected to ease off slightly over the same period.

Differences from average global sea surface temperatures for 24 December - 20 January 2018. Map courtesy of NOAA Climate Diagnostics. https://www.esrl.noaa.gov/psd/map/images/sst/sst.anom.month.gif
Monthly values of the Southern Oscillation Index (SOI), a measure of changes in atmospheric pressures across the Pacific, and the 3-month mean (black line). SOI mean values: January SOI 1.0; November-January average 0.6.
Differences from average January surface temperatures in the seas around New Zealand