Global setting: March 2016

El Niño conditions continued in the Tropical Pacific during March 2016, but the current event has clearly entered its decaying phase.

Sea surface temperature (SST) anomalies in the central and eastern Equatorial Pacific weakened further in March, with all SST indices now much weaker than 2oC above normal. The warmer sub-surface temperature anomalies across the eastern pacific have also weakened, while deeper cooler waters have spread eastward from the western Pacific. These changes in sub-surface temperatures make it very likely that the current SST anomalies will retreat further towards average in the next few months. Meanwhile, the Southern Oscillation Index (SOI) also weakened over March 2016 and the latest value (estimated on the 30th of March) is about -0.5.

International guidance indicates that El Niño is likely to weaken further over the next three months (April – June 2016) and the forecast is for a return to normal conditions or a transition toward La Niña by July – September 2016. La Niña conditions become increasingly likely towards the end of 2016 (over 45% chance for October – December 2016).

For April -June  2016, above normal pressure is forecast to the north of New Zealand. This circulation pattern is likely to be accompanied by weak anomalous westerly wind flow.

Sea Surface Temperatures

Sea surface temperatures around New Zealand are forecast to be above average, particularly to the west of the country.

Differences from average global sea surface temperatures for 13 March - 9 April 2016. 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 -0.4; January to March average -1.4.
Differences from average March surface temperatures in the seas around New Zealand.