An El Niño event in the tropical Pacific is now in place, but its duration and magnitude still remain uncertain. It is likely to be much weaker than the 1997–98 event, when there was lower than normal rainfall in many east coast areas, and severe drought in some localities. El Niños are typically, but not always, associated with below average temperatures and more frequent southwesterly winds over New Zealand. At this stage it is not possible to predict what effect this El Niño will have on the New Zealand climate in spring.
August to October temperatures are expected to show a north-south gradient, with temperatures likely to be above normal in northern North Island regions while tending towards normal or below normal in the South Island.
Rainfall is expected to be near normal over much of the country, but may be above average in eastern North Island regions. Similarly, soil moisture and river flow levels are expected to be normal everywhere except in the southeastern North Island, where they may be normal to above normal.
A. Climate models give no strong signals about how the climate will evolve, so we assume that there is an equal chance (33%) of the climate occurring in the range of the upper, middle or lower third (tercile) of all previously observed conditions.
B. There is a relatively strong indication by the models (60% chance of occurrence) that conditions will be below average, but, given the variable nature of climate, the chance of average or above-average conditions is also shown (30% and 10% respectively).