Global setting: August 2016

ENSO (El Niño – Southern Oscillation) neutral conditions continued in the tropical Pacific Ocean during August: sea surface temperatures along the eastern equatorial Pacific are near or slightly below normal, and the atmospheric conditions over the tropical Pacific are generally consistent with an ENSO-neutral state. As a whole the tropical ocean-atmosphere system still shows a leaning towards La Niña, but with a slight weakening of the signals that were observed last month (July 2016).

International guidance still favours development of La Niña conditions (55% chance) over the next three month period (September – November 2016), however the probability of neutral conditions over the next 3 months is almost equally as high (45% chance). The likelihood of La Niña conditions becoming established in the Pacific remains at a 55% chance for December – February 2016/2017. In summary, both the current state and recent evolution of the ocean-atmosphere system in the Pacific, as well as the models’ forecasts, suggest that if a La Niña event develops, it will be characterized by a relatively short duration and weak amplitude.

For September - November 2016, lower than normal pressure is forecast to the north-east of New Zealand while higher than normal pressure is expected to the south of the country. This airflow set-up is expected to produce more north-easterly winds than normal. The continuation of warmer than normal sea surface temperatures around the country suggests that warmer and more humid air masses are likely to affect New Zealand, especially the North Island.

Sea Surface Temperatures

Sea surface temperatures are forecast to remain above normal over the next three months, especially to the north of New Zealand.

Differences from average global sea surface temperatures for 31 July - 27 August 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: August SOI 0.6; June to August average 0.6.
Differences from average August surface temperatures in the seas around New Zealand.