The outlook for August 2004 to October 2004
Lower than normal mean sea-level pressures are expected in the Tasman Sea for early spring, with more northwesterly winds than usual over northern and central parts of New Zealand. Sea surface temperatures are likely to remain close to average around the country.
Air temperatures are expected to be average or above average for the North Island, and average for the South Island.
Rainfalls are expected to be near normal in all regions, except for above normal in Nelson. Normal soil moisture levels and streamflows are expected everywhere, except for the east coast of the South Island, where normal or below normal flows are likely.
There have been recent changes in the tropical Pacific towards a more coherent pattern of ocean and atmosphere anomalies that significantly increase the likelihood of an El Niño developing. At present, there appears to be an almost equal chance of either El Niño or ‘neutral’ conditions through spring–summer 2004–05. (Note that by ‘neutral’ we mean neither El Niño nor La Niña).
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).