Retrospective: October - December 2015 Outlook

During October - December 2015, above normal pressure was forecast to the north and west of New Zealand, while below normal pressure was expected to the east and south of the country.  This circulation pattern was likely to be accompanied by anomalous southwesterly wind flows - a signature of El Niño conditions.

Actual pressures were indeed higher than normal in the Tasman Sea while lower than normal pressures existed to the south-east of New Zealand. This pressure pattern produced a south-westerly flow anomaly.

Predicted air temperature: October – December 2015 temperatures were likely to be near average or below average for all regions of New Zealand.

Outcome: Actual temperatures were indeed near average across New Zealand. Pockets of below average temperature existed in Tararua and the Kapiti Coast while temperature in Central Otago was slightly above average.

Predicted rainfall: October – December 2015 rainfall was likely to be in the near normal or below normal ranges in the north and east of both the North and South Island.  Near normal rainfall was the most likely outcome for the west of the North Island.  In the west of the South Island rainfall about equally likely to be in the near normal or above normal range.

Outcome: Actual rainfall was below normal for virtually the entire country with the exception of Southland and coastal West Coast where rainfall was near normal. Rainfall was particularly low about South Wairarapa, Marlborough, Christchurch and coastal Hurunui where less than 40% of normal was recorded.

Weather station. [NIWA]