Global setting: September 2016

ENSO (El Niño – Southern Oscillation) neutral conditions are still present in the tropical Pacific Ocean as a whole, although some indicators are currently in the weak La Niña category. Sea surface temperatures (SSTs) in the central equatorial Pacific Ocean are near or slightly below average, and slightly above average in the western Pacific and off the South American coast. The atmospheric conditions over the tropical Pacific are generally consistent with an ENSO-neutral state, but show a leaning towards La Niña, as was already the case last month.

International guidance still slightly favours La Niña conditions (54% chance) over the next three months (October - December 2016) however neutral conditions are forecast to become slightly more likely than La Niña by January – March 2017 (50% chance for neutral) and the probability for La Niña drops sharply later on, with only 24% chance in April – June 2017. In summary, La Niña conditions are only slightly more likely than not over the next 3 months, and become less likely as we progress into the first half of 2017.

Despite the current borderline La Niña conditions and the only modest probability for La Niña to develop by the end of the year, the circulation pattern expected for October - December 2016 for the New Zealand region is broadly consistent with the typical La Niña signature: higher pressure than normal is forecast to the south and southeast of the country, while lower pressures than normal are forecast to the north of the New Zealand. These pressure anomalies are likely to be accompanied with easterly quarter flow anomalies.

Sea Surface Temperatures

Sea surface temperatures around New Zealand are forecast to remain near or above normal over the next three months.

Differences from average global sea surface temperatures for 4 September - 1 October 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: September SOI 1.3; July to September average 0.8.
Differences from average September surface temperatures in the seas around New Zealand.