NIWA Outlook: August-October 2014
Overview
The equatorial Pacific Ocean continues to remain ENSO-neutral at the end of July 2014, with atmospheric and oceanic
conditions failing to sufficiently couple to initiate an El Niño event. Other El Niño indicators have also weakened in
the last month. Thus, the chances of an El Niño event developing over spring appear to be lessening.
International guidance still indicates that El Niño is the most likely outcome (about 70% chance) over the coming three
seasons through to the end of summer 2015. However, it should be recognised that this guidance is based on model
simulations from end-of-June conditions so does not take account of the rapid changes observed in July. The behaviour of
the atmosphere over the next month or two will be critical to whether an El Niño event initiates or not.
During August–October 2014, mean sea level pressures are expected to be lower than normal to the northeast of New
Zealand, with higher pressures than normal to the southeast of the country. This pressure pattern is expected to be
accompanied by generally anomalous flow from the easterly quarter.
Sea surface temperatures for the coming three months are expected to be near average off the west coast of New Zealand
and above average to the east.
Outlook Summary
August-October temperatures are most likely (50% chance) to be above average for the east of the North Island, and
likely (40-45%) to be average or above average for all remaining regions of New Zealand. Cold snaps and frosts can still
be expected in some parts of the country as winter advances into spring.
August-October rainfall is equally likely (40% chance) to be normal or above normal in the north and east of the North
Island, and normal or below normal in the west of the North Island and in the north of the South Island. In remaining
South Island regions, seasonal rainfall is most likely (45%) to be in the near-normal range.
August– October river flows and soil moisture levels are about equally likely (35-40 % chance) to be normal or above
normal in the north and east of the North Island, and most likely (45%) to be below normal in the west of the North
Island. In the South Island, river flows and soil moisture levels are likely (40% chance) to be near normal in the west,
but about equally likely (35-40 % chance) to be normal or below normal in the north and east.