Climate Update 69 - March 2005

Backgrounder
Global setting
Temporary dip in the Southern Oscillation Index?
The Southern Oscillation Index (SOI), a measure of differences in atmospheric pressures across the Pacific, is a useful guide to the state of the El Niño-Southern Oscillation. However, its underlying 'message' is vulnerable to short-term pressure fluctuations.
The tropical Pacific Ocean is currently in a weak El Niño state, but there were rapid developments in aspects of ocean and atmosphere conditions in late February.

Climate Update is a summary each month of New Zealand’s climate, including soil moisture and river flows.
March 2005 – Number 69
February’s climate: New Zealand's eighth warmest February on record.
February’s river flows: Low stream flows in much of the North Island and the northern South Island.
Soil moisture levels: Below normal rainfall in many areas, but above normal in the southeast of the South Island.
Three-month outlook: Air temperatures average or below in the North Island and near average in the South Island; rainfall normal or below normal in the north an

The outlook for March 2005 to May 2005
Below average sea-level pressures are expected over the New Zealand and Tasman Sea region, with slightly enhanced southwesterly air flows across the country.
Air temperatures are expected to be average or below average in the North Island and near average in the South Island.
Rainfalls are likely to be normal or below normal in the north and east of the North Island and near normal elsewhere. Normal soil moisture conditions are expected throughout the country apart from normal or below normal in the east of the North Island.

Dry soils in the north
Soil moisture levels were well below normal in much of the North Island at the end of February. The northeast coast of the South Island was also drier than normal. Otago soils had near normal moisture, while Southland moisture levels were higher than normal.
 
Soil moisture deficit in the pasture root zone at the end of February (right) compared with the deficit at the same time last year (centre) and the long-term end of February average (left). The analysis is done for an average soil type where the available water capacity is taken to be 150 mm.