Seasonal climate outlook: December 2016 - February 2017

01 December 2016

Overview

The tropical Pacific exhibits mainly neutral ENSO (El Niño-Southern Oscillation) conditions.

Sea surface temperatures (SSTs) in the central Equatorial Pacific Ocean are marginally below average and do not exceed the threshold used by NOAA’s Climate Prediction Center to define La Niña events. Additionally, sub-surface temperatures in the central and eastern Pacific Ocean (150°W to 110°W) have continued to warm, a signal from the ocean that La Niña conditions are easing. The atmospheric setup is mixed, as stronger easterly trade winds in the western Pacific along with enhanced convection north and east of Papua New Guinea are consistent with weak La Niña conditions. However, the Southern Oscillation Index (SOI) remains weakly negative and is consistent with ENSO-neutral conditions.

International guidance still slightly favours La Niña conditions (53% chance) over the next three month period (December 2016 - February 2017). However, neutral conditions are much more likely than La Niña by March - May 2017: 80% chance for neutral, and only 16% for La Niña. In summary, La Niña conditions are only slightly more likely than not over the next 3-month period, and become significantly less likely as we progress into 2017. 

Consequently, the combination of easing La Nina conditions, along with the absence of other large-scale climate drivers this summer, results in no clear air flow anomaly. Typical summer conditions are expected of anticyclones crossing the North Island and prevailing westerly winds over the South Island.

NIWA Forecaster—Chris Brandolino—discusses the December 2016 - February 2017 seasonal climate outlook.

NIWA’s Seasonal Climate Outlook: December 2016 - February 2017

Watch Video

Outlook summary

December 2016 – February 2017 temperatures are most likely to be near average (45% chance) for the west of the North Island and are about equally likely to be near average or above average (40-45% chance) for the remainder of the country. Sea surface temperatures around New Zealand are expected to be near average or above average over the next three months.

December 2016 – February 2017 rainfall totals are about equally likely to be near normal or below normal (35-40% chance) for the east of the South Island and mostly likely to be near normal (45% chance) for the rest of New Zealand.   

December 2016 – February 2017 soil moisture levels and river flows are most likely to be near normal (45-50% chance) for the north and east of the North Island, and equally likely (40% chance) to be near normal or above normal for the west of the North Island.  Near normal or above normal soil moisture and river flows are equally likely (40% chance) for the north of the South Island with near normal (45% chance) soil moisture and river flows the most likely outcome for the west of the South Island. Near normal or below normal soil moisture and river flows are about equally likely (35-40% chance) for the east of the South Island.

Regional predictions for the December 2016 – February 2017 season

Northland, Auckland, Waikato, Bay of Plenty

The table below shows the probabilities (or percent chances) for each of three categories: above average, near average, and below average. In the absence of any forecast guidance there would be an equal likelihood (33% chance) of the outcome being in any one of the three categories. Forecast information from local and global guidance models is used to indicate the deviation from equal chance expected for the coming three month period, with the following outcomes the most likely (but not certain) for this region:

Temperatures are about equally likely to be near average (40% chance) or above average (45% chance).
Rainfall totals are most likely to be in the near normal range (45% chance).
Soil moisture levels and river flows are most likely to be near normal (45% chance).