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 69 - March 2005
Outlook and outcome – December 2004 to February 2005
Rainfall was as forecast in the north and southwest of the North Island, and in north Canterbury, Central Otago, and Southland. It was wetter than predicted elsewhere in the east, and lower than predicted elsewhere in the west.
Air temperatures were lower than forecast in parts of the North Island, but generally average or below average as predicted in the South Island.
Streamflows were normal to above normal in much of the North Island, apart from Hawke’s Bay and the east coast where they were below normal.
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
New Zealand Climate
February 2005 was one of the warmest on record.
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.
Below normal flows in the north
Stream flows were below normal in most of the North Island apart from Northland, and in the northern South Island as far as North Canterbury. Elsewhere in Northland, and in the rest of the South Island, stream flows were normal to above normal.
Percentage of average February streamflows for rivers monitored in national and regional networks. The contributing catchment area above each monitoring location is shaded. NIWA field teams, regional and district councils, and hydro-power companies are thanked for providing this information.
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.