Three-month outlook

The outlook for September to November 2002

An El Niño event is under way in the tropical Pacific, but is likely to be much weaker than the 1997-98 episode. However, spring climate in New Zealand is expected to be influenced by the above average local sea surface temperatures and enhanced trough activity across southern New Zealand, rather than by typical El Niño conditions of cooler southwesterlies.

Most climate models predict that El Niño will continue through summer 2002-03, when drier conditions could develop in the north and east of the North Island, and the eastern South Island from north Canterbury through to Nelson.

For September to November, temperatures are expected to be above average or average over the North Island and northern South Island, and near average over the rest of the South Island. Rainfall is expected to be near normal in all regions.

Soil moisture levels and river flows are expected to be normal everywhere, apart from normal or below normal river flows for the northern South Island.

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).