Global setting: February 2018

Weak La Niña conditions continued in the tropical Pacific during February 2018, but the current state of the Ocean – Atmosphere system in the Equatorial Pacific indicates that it is now reaching its decay phase. Below average sea surface temperatures (SSTs) remained present in the central and eastern equatorial Pacific Ocean but weakened compared to January 2018

The consensus from international models is for the tropical Pacific to rapidly transition to an ENSO-neutral state over the next 3 month period (69% chance over March – May 2018). ENSO-neutral remains the most likely outcome over the winter season (June – August 2018), and a transition towards El Niño becomes increasingly likely thereafter (45% chance for El Niño conditions to emerge over the September – November 2018 period).

For March – May 2018, the atmospheric circulation around New Zealand is forecast to be characterised by lower than normal atmospheric pressure northwest of the country, extending over parts of New Zealand, unsettled conditions especially for the North Island, and weak northeasterly quarter flow anomalies. This pressure pattern, in concert with the anomalously warm ocean waters around the country, is expected to be associated with warmer than average temperatures, and above normal rainfall - notably for the North Island.

 Sea Surface Temperatures

Ocean waters remain much warmer than average all around New Zealand, in the Tasman Sea, and in the Southwest Pacific. While the anomalies for coastal New Zealand weakened compared to the peak reached at the end of January 2018, they remain close to or exceed + 1oC. According to the dynamical models’ forecasts, warmer than average SSTs are likely to persist for at least part of the next 3 months (March – May 2018).

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: February SOI -0.6; December-February average 0.1.
Differences from average February surface temperatures in the seas around New Zealand