Retrospective: December – February 2018 Outlook
For December 2017 – February 2018, the atmospheric circulation around New Zealand was forecast to be characterised by higher pressure than normal to the south and southeast of the country, and lower pressure than normal to the north. This pressure pattern was expected to be associated with easterly to northeasterly flow anomalies, a pattern consistent with La Niña. Actual pressures were slightly lower than normal to the northwest of the country and slightly higher than normal to the south east of the country. There was no significant flow anomaly for the season as whole.
Predicted air temperature: December 2017 – February 2018 temperatures were forecast to be above average, with high confidence, for all regions of New Zealand.
Outcome: Actual temperatures were well above average for all regions.
Predicted rainfall: For December 2017 – February 2018 rainfall totals were most likely to be above normal in the north of the North Island, equally likely to be near normal or above normal for the east of the North Island. For the west of the North island and north of the South Island, rainfall amounts were most likely to be in the near normal range. Below normal rainfall was most likely for the west of the South Island and normal or below normal was forecast for the east of the South Island.
Outcome: Actual rainfall was above normal for Northland, Auckland, Waikato, Bay of Plenty, Wellington as well as the north and east of the South Island. Rainfall was mostly near normal elsewhere. Small areas of below normal rainfall occurred in Southland and Gisborne.