Science Centres: Climate

Global setting and climate outlook

El Niño-Southern Oscillation remains neutral despite positive SOI

Difference from average global SST (click to enlarge).

Monthly SOI values (click to enlarge).

Neutral ENSO conditions in the tropical equatorial Pacific are now well established, although lingering effects of La Niña persist. The Southern Oscillation Index remains positive, having strengthened somewhat during September to +1.4 with the three-month mean at +0.8. The positive sea surface temperature anomalies in the eastern Pacific reduced during the month. At present, all seasonal climate models suggest that ENSO-neutral conditions will continue until the end of the year.

Sea surface temperatures(SST) around New Zealand

New Zealand SST (click to enlarge).

Sea surface temperature (SST) anomalies in the New Zealand region overall are close to but slightly cooler than average. The September SST anomaly was –0.2 °C, with a negligible average anomaly for the three months July to September. Sea surface temperatures around New Zealand are expected to remain near normal until the end of the year.

Outlook for October to December 2008

Regional outlook (click to enlarge).

In the New Zealand region, mean sea level pressures are likely to be higher than normal, especially over the South Island, resulting in lighter winds than usual over the country and periods of easterlies affecting the North Island. Air temperatures are likely to be average or above average over the north and west of the South Island and average elsewhere. Rainfall is likely to be normal or below normal over much of the country, with near normal rainfall in the east of the North Island. Normal or below normal soil moisture levels and stream flows are likely everywhere in the country.

Under the prevailing neutral conditions of the El Niño–Southern Oscillation, there is a 4 out of 5 chance of an ex-tropical cyclone passing within 500 km of the country between November and May, with the highest risk in the Northland and Gisborne districts.