Global setting & climate outlook

Global setting

Weak La Niña

Difference from average global SST (click to enlarge).

Monthly SOI values (click to enlarge).

The state of the tropical Pacific Ocean and atmosphere is now characteristic of weak La Niña conditions. Trade winds across the equatorial region of the Pacific are stronger than normal, and convection is enhanced over northern Australia and Indonesia.

The Southern Oscillation Index (SOI) rose above +1 in January, from a neutral value in December (-0.1). The 3-month mean SOI is still in the neutral range. The weak La Niña may ease to neutral conditions by winter 2006.

For the tropical cyclone season through to April 2006, normal cyclone activity is expected. For New Zealand, this means a 70% chance of a cyclone affecting the country over the next three months.

Sea surface temperatures (SST) around New Zealand

New Zealand SST (click to enlarge).

The average difference from the historical normal SST in the New Zealand region eased in January, in association with cooler enhanced westerly atmospheric circulation. The SST anomaly was about +0.3 °C in January, down from +0.8 °C in December, and +0.6 °C for the three month November to January average.

Outlook for February 2006 to April 2006

Regional outlook (click to enlarge).

Westerly wind patterns over New Zealand during February-April are likely to be weaker than normal. Air temperatures are expected to be average or above average in all districts.

Rainfalls are expected to be near normal in most places, but normal or below normal in the southwest of the North Island and the east of the South Island. Normal or below normal soil moisture levels and below normal streamflows are expected in the southwest of the North Island and the east of the South Island, with mostly normal soil moisture and stream flow conditions elsewhere.