Global setting and climate outlook
Global setting and climate outlook
La Niña dominates
Difference from average global SST (click to enlarge).
Monthly SOI values (click to enlarge).
During December, La Niña conditions strengthened into a moderate to strong event that is likely to persist through autumn. The ‘horseshoe’ of warm sea surface water (see map) continues in the extra-tropics of both hemispheres. Easterly trade winds were strong and persistent during December over a wide longitude band, including west of the Date Line. The SOI continued its strong movement upwards, being +1.4 for December (+0.9 November), with an October to December average of +0.9.
Sea surface temperatures(SST) around New Zealand
Sea surface temperature (SST) anomalies in the New Zealand region reversed the trend seen in October and November, with positive anomalies (above average temperatures) developing, consistent with a La Niña event. The December SST anomaly in the New Zealand reference area was +0.3 °C, with an October to December average anomaly of about +0.1 °C. The most persistent positive anomalies are spreading in from the west of the country.
Outlook for January to March 2008
Regional outlook (click to enlarge).
Late summer average atmospheric sea level pressures are expected to be higher than normal over the South Island, and lower than normal to the north, with more easterly or northeasterly windsthan normal across the North Island, and lighter than normal winds across the South Island.
Air temperatures are likely to be above average across the country. Rainfall is expected to be above normal in northern North Island, below normal in the west, south, and east of the South Island, and near normal elsewhere. Soil moisture levels and stream flows are likely to be above normal in the north of the North Island, and below normal in the southwest of the North Island and in the west, south, and east of the South Island.
Tropical cyclone risk is normal through to May 2008. Should one approach New Zealand, the regions most at risk are the north and northeast of the North Island.