For February – April 2018, the atmospheric circulation around New Zealand was forecast to be characterized by higher pressures than normal east and south of the country, while lower pressure than normal was forecast over the Tasman Sea, extending over the North Island. This pressure pattern, in concert with the marine heatwave, was expected to be associated with warmer than average air temperatures, occasional significant rainfall events, and flow anomalies from the northeasterly quarter. Actual pressures were lower than normal across the country with a north-westerly flow anomaly across the North Island and no significant flow anomaly for the South Island.
Predicted air temperature: February – April 2018 temperatures were forecast to be above average for all regions of New Zealand with high confidence.
Outcome: Actual temperatures were above average for the North Island and the coastal fringes of the South Island and near normal elsewhere.
Predicted rainfall: February – April 2018, rainfall totals were forecast to be above normal in the North Island and in the north of the South Island and about equally likely to be near normal or above normal in the west and east of the South Island.
Outcome: Actual rainfall was above normal for much of the country. Rainfall was near normal for small parts of Gisborne, the West Coast and Southland.