Global setting: March 2017

The tropical Pacific is currently in an ENSO (El Niño – Southern Oscillation) neutral state (neither El Niño nor La Niña).

Sea surface temperatures (SSTs) in the central Equatorial Pacific Ocean are marginally below average. In the sub-surface ocean, the pockets of cooler than average temperatures that remained in December 2016 have all but dissipated and slightly warmer than normal ocean waters are now present in the western equatorial Pacific. The Southern Oscillation Index is close to zero for January 2017. Except for some aspects of rainfall and convection anomalies along the equatorial Pacific, the weak La Niña-like signals that were present in previous months have now vanished.

International guidance favours ENSO-neutral conditions with high probability (90% chance) over the next three month period (February - April 2017). Later during the year, the models indicate substantial chances for a return to El Niño conditions (37% in August – October 2017), but note that ENSO forecasts beyond the Southern Hemisphere autumn are known to be less reliable than at other times of the year.

With the likely persistence of ENSO-neutral conditions, and the anticipated absence of other large- scale climate drivers over the next three months, the atmospheric circulation around New Zealand is expected to favour only slightly more westerly to south-westerly wind flows than normal.

Sea Surface Temperatures

Water temperatures surrounding New Zealand are close to or slightly below average. Along the immediate New Zealand coastline, sea surface temperatures (SSTs) are generally below to much below normal for the time of year. SSTs are, however, much warmer than average in the western part of the Tasman and along the east coast of Australia. The dynamical models’ forecasts for SSTs indicate that this pattern is likely to persist over the next three month period. Thus, coastal waters around the country are expected to be near or slightly below average as a whole for February – April 2017.

Differences from average global sea surface temperatures for 19 March - 15 April 2017. Map courtesy of NOAA Climate Diagnostics Centre (http://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: March SOI +0.5; January-March average +0.2.
Differences from average March surface temperatures in the seas around New Zealand