NIWA has published it’s climate outlook for the next three months:
La Niña weakening, with a mild end to autumn
La Niña is on the wane, and the end of autumn and start of winter looks likely to be mild.
The NIWA National Climate Centre says that, on average over the next three months, above average temperatures are likely in several regions of the country1. It is not likely that any major region will be cooler than normal over the three months as a whole, although this does not rule out occasional cold spells.
The latest NIWA Seasonal Climate Outlook, issued today by the National Climate Centre, indicates that the moderate La Niña in the tropical Pacific is expected to weaken to neutral conditions by early winter.
The latest outlook covers the three months April, May and June 2009, and indicates average or above average temperatures in all regions. While most regions are expected to experience near normal rainfalls for the three months as a whole, below normal rainfall is likely for the eastern South Island, and normal or above normal rainfall is likely over the north of the North Island.
Normal or above normal soil moisture and stream flows are likely in the northern North Island, while near normal conditions are likely over the rest of the North Island and northern South Island. Normal or below normal soil moisture and stream flows are expected in the rest of the South Island.
Mean sea-level pressures are likely to be higher than normal to the east and south of the country, and lower than normal to the north of New Zealand, resulting in a northeast flow anomaly, especially over the North Island.
For the remainder of the tropical cyclone season (through to May 2009), there is an average chance of an ex-tropical cyclone passing within 500 km of the country.
Overall Picture
Temperature:
Temperatures are expected to be average or above average in all regions. Sea surface temperatures around New Zealand are expected to be average or slightly above average by the start of winter.
Rainfall, soil moisture, and stream flows:
Rainfall is likely to be normal or above normal over the north of the North Island, below normal along the east coast of the South Island, and near normal elsewhere. Soil moisture and stream flows are likely to be normal or above normal in the northern North Island, while near normal conditions are likely over the rest of the North Island and northern South Island. Normal or below normal soil moisture and stream flows are expected in the rest of the South Island.
Regional predictions for the next three months:
Northland, Auckland, Waikato, Bay of Plenty:
Above average temperatures are likely. Rainfall, soil moisture levels, and stream flows are likely to be normal or above normal for the season as a whole.
Central North Island, Taranaki, Wanganui, Manawatu and Wellington:
Average or above average temperatures are likely. Normal rainfall, stream flows, and soil moisture levels are likely for the three-month period.
Gisborne, Hawke’s Bay, Wairarapa:
Above average temperatures are likely for the three months. Normal rainfall, soil moisture levels and stream flows are likely overall.
Nelson, Marlborough, Buller:
Average or above average temperatures are likely. Rainfall is likely to be near normal, and soil moisture levels and stream flows are also likely to be near normal.
West Coast, Alps and Foothills, Inland Otago, Southland:
Above average temperatures are likely. Rainfall is likely to be near normal, while soil moisture levels and stream flows are likely to be normal or below normal.
Coastal Canterbury, East Otago:
Average or above average temperatures are likely for April-June. Rainfall is likely to be below normal, and soil moisture levels and stream flows are likely to be normal or below normal.
Background
In the New Zealand region, mean sea level pressures are likely to be higher than normal to the east and south of the country, and lower than normal to the north of New Zealand, resulting in a northeast flow anomaly, especially over the North Island. Sea surface temperatures around New Zealand are expected to be average or slightly above average through to the start of winter.
A moderate La Niña in the tropical Pacific is expected to weaken to neutral conditions by the end of the period.
The tropical cyclone season for the southwest Pacific runs from November to May. With current conditions in the Pacific, there is a near average chance of an ex-tropical cyclone passing within 500 km of the country during the last two months of the season (April-May). The districts at highest risk are Northland and Gisborne.