Retrospective - July to September Outlook

Over the early spring period, neutral conditions (neither La Niña nor El Niño) were expected to give way to the development of an El Niño.  To reflect this, circulation in the New Zealand region was forecast to transition from northeasterly to westerly flow anomalies by the end of the season, as El Niño conditions settled in.  This was a correct forecast, as threshold El Niño conditions were present by September, and although the seasonal (July-September) circulation anomaly over New Zealand was northeasterly, September was notable for more westerly to northwesterly flows than usual.

Predicted rainfall: Rainfall totals are likely to be normal or below normal in South Island regions and in the east of the North Island, but near normal in the north and west of the North Island. 

Outcome: Rainfall was generally correctly forecast in the north and west of the North Island where near normal rainfall totals were recorded. The exceptions were the Far North, Coromandel and the Western Bay of Plenty (with above normal rainfall observed), and the Kapiti Coast (with below normal rainfall experienced). Seasonal rainfall for July-September was predicted to be normal or below normal in all other regions. Rainfall in the west and south of the South Island was correctly forecast (it being a rather dry early spring period there), but it was wetter than forecast everywhere else. Patches of above normal rainfall were seen in parts of: Gisborne, southern Hawkes Bay, coastal Wairarapa. Nelson City, Marlborough and the Kaikoura Coast, south Canterbury and north Otago. 

Predicted air temperature: Temperatures are likely to be near average overall, except for the west and south of the South Island, where average or above average temperatures are likely. 

Outcome: Temperatures were correctly forecast as being average or above average in the west and south of the South Island, but in other areas it was generally warmer than forecast, with above average temperatures observed across much of the eastern South Island, Nelson/Marlborough, and the north and west of the North Island.  For the eastern North Island, temperatures were patchy, but typically on the border of between average and above average.