Global setting: December 2015

Sea surface temperature anomalies in the central and eastern Pacific have weakened slightly, but still exceed +2oC.

The SOI is weakly negative at -0.6 for the month of December; however, strong westerly wind anomalies (weaker easterly trade-winds) continue to affect the western and central Pacific. Several ENSO indicators showed a weakening in the last two weeks, raising the possibility that El Niño could have reached its peak at the end of 2015. However, the current event is expected to remain in the strong category for the next three months, and the impacts of El Niño on New Zealand’s climate will likely persist into autumn. 

International guidance indicates that El Niño conditions will continue (100% probability) over the next three months (January – March 2016) and will rapidly decay thereafter, with a return to normal conditions or a transition to La Niña conditions by July – September 2016.

For January - March 2016, above normal pressure is forecast to the north of New Zealand, while below normal pressure is expected to the south of the country.  This circulation pattern is likely to be accompanied by anomalous westerly wind flows – a signature consistent with El Niño.

Sea surface temperatures

Sea surface temperatures are forecast to be below normal to the east of New Zealand.

Differences from average global sea surface temperatures for 13 December 2015 - 09 January 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: December SOI -0.6; October to December average -1.1.
Differences from average December surface temperatures in the seas around New Zealand.