For September – November 2017, the atmospheric circulation around New Zealand was forecast to be characterised by lower pressure than normal west of New Zealand and higher pressure than normal to the south and east of the country. This was expected to lead to northerly-quarter flow anomalies over the three months. Periodic easterly flow anomalies were also possible, consistent with a La Niña-like signal in the atmosphere. This type of atmospheric setup would lend itself to subtropical moisture connections associated with heavy rainfalls for New Zealand. Actual pressures were near normal around New Zealand with no significant air flow anomalies.
Predicted air temperature: September – November 2017 temperatures were forecast to be above average for all regions of New Zealand.
Outcome: Actual temperatures were near average for Northland, Auckland, western Waikato, Gisborne, Wellington and coastal margins of Marlborough and Canterbury. Temperatures were above average for the remainder of the country.
Predicted rainfall: September – November 2017 rainfall totals were about equally likely to be normal or above normal for the North Island and the north of the South Island and most likely to be near normal for all remaining regions of New Zealand.
Outcome: Actual rainfall was near normal for much of the North Island. The exceptions were coastal Bay of Plenty were above normal rainfall was recorded and parts of Wellington and Hawke’s Bay where rainfall was below normal. In the South Island rainfall was near normal for the majority of Tasman, Marlborough and northern Canterbury and below normal for the remainder of the island.