Global setting and climate outlook

Global setting

El Niño-Southern Oscillation remains neutral

Difference from average global SST (click to enlarge).

Monthly SOI values (click to enlarge).

The tropical Pacific Ocean is likely to remain in a neutral state (no El Niño or La Niña) until autumn 2006. The pool of cold water off the South American coast has increased during November, while surface water near the date line remained warm.

The Southern Oscillation Index was weakly negative in November (-0.4), with the 3-month September to November average at +0.3. The equatorial trade winds are near normal strength.

Normal tropical cyclone activity is expected in the Pacific until April 2006. For New Zealand, this means a 70% chance of a cyclone passing somewhere near the country, with Northland and Gisborne being most at risk. The risk is greatest after the end of January.

Sea surface temperatures (SST) around New Zealand

New Zealand SST (click to enlarge).

The New Zealand average difference from the historical normal SST was about +0.8 °C for November and +0.6 °C for the September to November average. Surface warters were warmer than normal over much of the Tasman Sea, around the New Zealand coast, and to the northeast of the country.

Outlook for December 2005 to February 2006

John Clayton samples a luxuriant carpet of bryophytes at 20-m depth in Lake Rotoroa, Nelson. (Photo: R. Wells)
 

Regional outlook (click to enlarge).

Atmospheric circulation patterns over New Zealand during summer (December-February) are likely to be characterised by weaker than normal westerly winds. Air temperatures are expected to be above average or average in all regions of New Zealand.

Rainfall is likely to be normal or above normal in the north and east of the North Island, normal or below normal in the west and south of the South Island, and near normal elsewhere. Soil moisture levels and river flows are expected to be below normal in the southwest of the North Island and all of the South Island, with normal conditions in the north and east of the North Island.