Global setting: May 2018

ENSO-neutral conditions persisted in the tropical Pacific during May 2018. The Southern Oscillation Index (SOI) was positive at about +0.3 during the past 30 days. Sea surface temperatures (SSTs) in the central and eastern equatorial Pacific Ocean warmed for the second consecutive month and are now near or slightly above average for the time of year.

The consensus from international forecast models is for the tropical Pacific to persist in an ENSO-neutral state over the next 3 month period (67% chance over June – August 2018). However, during late winter and early spring (August – October 2018), El Niño conditions are slightly favoured (45% chance) over ENSO-neutral (44% chance).

The atmospheric circulation around New Zealand is forecast to be characterized by mixed flow patterns during June-August 2018. Periodic easterly-quarter (NE to SE) air flows are signalled during June which may give way to more westerly or southwesterly air flows during July and/or August.

Sea Surface Temperatures

Sea surface temperatures (SSTs) within New Zealand’s immediate coastal waters continued to decrease during May and are now near or slightly above average. According to the dynamical models’ forecasts, near average SSTs are expected in New Zealand coastal waters during the next 3 months (June-August 2018).

In the absence of large-scale climate drivers and near-average regional SSTs, forecast predictability outside of the tropics, including New Zealand, may be lower than normal over the coming three-month period.

Differences from average global sea surface temperatures for 13 May - 9 June 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: May SOI 0.3; March-May average 0.6.
Differences from average May surface temperatures in the seas around New Zealand