Retrospective - July to September Outlook

For July–September 2013 higher pressures than normal were forecast south of New Zealand, with slightly lower pressures than normal in the north Tasman Sea. This circulation pattern was expected to produce a weak easterly flow anomaly over the country. Much lower than normal pressures occurred south of Australia extending towards southern New Zealand for the forecast period and much higher than normal pressures occurred to the east country. Consequently, more easterly airflows than usual occurred across the north of New Zealand, with more disturbed north-west flows across the southern half of the South Island.

Neutral conditions (neither El Niño nor La Niña) were expected to persist over the July–September period. This forecast was well advised with ongoing ENSO-neutral conditions prevailing over the equatorial Pacific Ocean.

Predicted rainfall: Rainfall for the July–September period as a whole was expected to be normal or above normal in the east of the North Island, normal or below normal in the west and south of the South Island, and in the near normal range for all other regions.

Outcome: This rainfall forecast was correct for many areas of the country. Well above normal rainfalls were recorded across much of the Hawkes Bay and Gisborne, and near normal rainfall overall was recorded in the north of both islands as well as the west of the South Island (save the south-western extreme of Southland where rainfall in excess of 120% of normal was recorded). However, it was much drier than expected along the coastal strip between Ashburton and the Waitaki Districts where rainfall was between 40-80% of normal. Rainfall was also below normal across parts of northern New Plymouth, southern Waitomo and much of the Waikato.

Predicted air temperature: Temperatures were expected to be above average in all North Island regions, and likely to be average or above average in all South Island regions for June–August.

Outcome: This forecast was correct for all regions of the country. In the North Island temperatures were between 0.5-1.0°C above average across most areas, although small pockets of closer to normal conditions were recorded in parts of the Waitomo, Auckland and Far North Districts. In the South Island, above normal temperatures were recorded across all regions in the South Island, with temperatures in excess of 1.5°C above average across inland areas of Southland and Otago.