Retrospective: October-December 2017 Outlook
For October – December 2017, the atmospheric circulation around New Zealand was forecast to be characterized by lower pressure than normal northwest of New Zealand and higher pressure than normal to the south and east of the country. This type of atmospheric setup, with anomalous north-easterly airflow, can produce streams of subtropical moisture towards New Zealand associated with heavy rainfalls. Actual pressures were higher than normal over the country with an easterly quarter air flow anomaly.
Predicted air temperature: October – December 2017 temperatures were forecast to be above average for all regions of New Zealand.
Outcome: Actual temperatures were indeed above average for all regions, particularly in the South Island. Small pockets of near average temperatures were found in coastal Gisborne and coastal parts of southern Canterbury.
Predicted rainfall: October – December 2017 rainfall totals were likely to be normal or above normal for the north of the North Island, and most likely to be near normal for the remainder of the North Island and the north, west and south of the South Island. For the east of the South Island, rainfall was equally likely to be near normal or below normal.
Outcome: Actual rainfall was below to well below normal for much of the country. Parts of Hawke’s Bay, coastal Fiordland and small areas in northern Canterbury were the only places to see near normal rainfall.