Seasonal Climate Outlook: December 2013 - February 2014

03 December 2013

The equatorial Pacific Ocean continues in a neutral state (neither El Niño nor La Niña) in November 2013.

International guidance indicates that ENSO-neutral conditions are very likely to persist for the next three months (December 2013 – February 2014). These ENSO-Neutral conditions are forecast to continue throughout the summer and early autumn, but El Niño development becomes increasingly likely as we approach winter, reaching approximately 50/50 percent chance along with ENSO neutral from May-July 2014.

For the coming three months as a whole in the New Zealand region, lower pressures than normal are forecast to the north of the country in the western Pacific, while anticyclonic conditions are forecast over the south and to the east of the New Zealand. This circulation pattern is expected to be associated with slightly less westerly and southwesterly airflow than usual over the summer.

Sea surface temperatures are expected to remain above average around the whole of New Zealand for the coming three months.

Outlook summary

Temperatures over the December–February period as a whole are equally likely (40% chance) to be near average or above average in the north and east of the North Island and the east of the South Island, while above average temperatures are the most likely outcome (45 to 50 % chance) for the remaining regions of the New Zealand.

Rainfall totals over the December–February period as a whole are most likely (45% chance) to be near normal in all regions except for the north of the North Island, where rainfall is equally likely (40% chance) to be near normal or above normal.

Soil moisture levels are most likely (45 %) to be near normal in all regions but for the east of the South Island, where normal and below normal soil moisture levels are equally likely (40 %). River flows for December 2013 – February 2014 are forecast to be near normal (35 to 40 %) or below normal (35 %) in the north and west of the North Island, as well as in the north and west of the South Island. Normal river flows are most likely (40 %) in the east of the North Island, while below normal river flows are most likely in the east of the South Island (45 % chance). On the basis of this forecast, coastal Canterbury and east Otago are most likely to experience drier than normal conditions over the summer.

Regional predictions for the December to February 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 and rainfall totals are equally likely (40% chance) to be in the near average or above average range.
Soil moisture levels are most likely (45%) to be in the near normal range.
River flows are equally likely (35%) to be in the below normal or near normal range. Note that this is not very different from the probability of above normal river flows (30 %), meaning that the uncertainty in the forecast is high for the December – February period as a whole.

Other outcomes cannot be excluded. The full probability breakdown is:

	Temperature	Rainfall	Soil moisture	River flows
Above average	40	40	25	30
Near average	40	40	45	35
Below average	20	20	30	35

Click here to view the historic rainfall and temperature for this region