September 2013 was characterised by much lower pressures than normal around much of the New Zealand region, except for an area of higher pressures than normal to the east of the North Island, and another area of high pressure well to the south of the country. This pressure pattern caused more west to southwest flows across New Zealand. These unstable flows caused numerous storms and fronts to affect the country in September, including a severe wind storm in Canterbury early in the month.
New Zealand Climate Update 172 - October 2013
What happened in September, how our climate outlook for the previous three months turned out, global and local sea temperatures, and our outlook for October to December.
The equatorial Pacific Ocean continues in a neutral state (neither El Niño nor La Niña), with recent cooler-than-normal sea-surface conditions (La Niña-like) in the eastern tropical Pacific having weakened. International guidance indicates that ENSO-neutral conditions are the most likely outcome for the next three months (October–December). In the New Zealand region, higher pressures than normal are forecast to south of the country and lower pressures than normal are forecast in the Australian Bight extending eastwards into the central Tasman. This circulation pattern is expected to produce northerly quarter flows over the north of the country, and a slightly enhanced easterly flow over the lower South Island.
Rainfall for the October - December period is likely to be normal or above normal in the north of the North Island, and near normal for the rest of New Zealand.
Temperatures over the October - December period are likely (50% chance) to be above average in the east of the North Island and the north of the South Island, and average or above average in all other regions.
Soil moisture levels are likely to be normal or above normal in the north of the North Island, and near normal for all other regions.
River flows are likely to be normal or above normal in the north of the North Island, and near normal for all remaining regions.
See our three month Seasonal Climate Outlook for more detail.
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.