The NIWA National Climate Outlook

The NIWA National Climate Centre’s outlook for summer, December 2011 to February 2012, indicates that seasonal temperatures are likely to be above average on the West Coast of the South Island, and near average or above average across the remainder of the country.
Summer rainfall totals are likely to be below normal on the West Coast, and normal or below normal across the remainder of the South Island, as well as in the southwest of the North Island. Near normal seasonal rainfall is likely for the eastern North Island. For the northern North Island, summer rainfall is equally likely to be normal or above normal. Soil moisture levels and river flows are likely to be near normal in eastern regions of both Islands, and normal or below normal elsewhere.

La Niña conditions are likely to continue through the summer, according to the NIWA National Climate Centre, although it is unlikely that the current La Niña event will be as strong as the previous La Niña event of 2010-11.

The outlook states that mean sea level pressures during the summer are likely to be above normal across the South Island, with weaker than normal westerlies over the North Island.
For the tropical cyclone season (through until May), the chance of an ex-tropical cyclone passing close to New Zealand is below the long-term average. On average, at least one ex-tropical cyclone passes within 500km of New Zealand in 9 out of 10 cyclone seasons.
Overall Picture

Temperature:
For the December-February period as a whole, air temperatures are likely to be above average on the West Coast of the South Island, and near average or above average across the remainder of the country. Sea surface temperatures are likely to remain above average to the northeast of the North Island during summer, but near average elsewhere about the New Zealand region.

Rainfall, soil moisture, and river flows:
The National Climate Centre projects that summer rainfall totals are likely to be below normal on the West Coast, and normal or below normal across the remainder of the South Island, as well as in the southwest of the North Island. Near normal seasonal rainfall is likely for the eastern North Island. For the northern North Island, summer rainfall is equally likely to be normal or above normal. Soil moisture levels and river flows are likely to be near normal in eastern regions of both Islands, and normal or below normal elsewhere.

Regional predictions for the next three months:

Northland, Auckland, Waikato, Bay of Plenty:
Summer temperatures are equally likely to be near average or above average. Seasonal rainfall totals are equally likely to be near normal or above normal. Soil moisture levels are likely to be in the normal range for the season as a whole, while river flows are likely to be normal or below normal.

Probabilities are assigned in three categories; above average, near average, and below average. The full probability breakdown is:

Temperature Rainfall Soil moisture River flows
Above average 40% 40% 30% 25%
Near average 40% 40% 40% 40%
Below average 20% 20% 30% 35%

Central North Island, Taranaki, Wanganui, Manawatu and Wellington:
Seasonal temperatures are equally likely to be near average or above average. Summer rainfall totals, soil moisture levels, and river flows are likely to be near normal or below normal, for the three month season as a whole.

Probabilities are assigned in three categories; above average, near average, and below average. The full probability breakdown is:

Temperature Rainfall Soil moisture River flows
Above average 40% 20% 25% 20%
Near average 40% 40% 40% 40%
Below average 20% 40% 35% 40%

Gisborne, Hawke’s Bay, Wairarapa:
Summer temperatures are equally likely to be near average or above average. Seasonal rainfall totals, soil moisture levels, and river flows are all likely to be in the near normal range.

Probabilities are assigned in three categories; above average, near average, and below average. The full probability breakdown is:

Temperature Rainfall Soil moisture River flows
Above average 40% 30% 30% 25%
Near average 40% 50% 40% 45%
Below average 20% 20% 30% 30%

Nelson, Marlborough, Buller:
Temperatures over the summer period are equally likely to be near average or above average. Seasonal rainfall totals, soil moisture levels, and river flows are likely to be near normal or below normal.

Probabilities are assigned in three categories; above average, near average, and below average. The full probability breakdown is:

Temperature Rainfall Soil moisture River flows
Above average 40% 20% 25% 25%
Near average 40% 40% 40% 40%
Below average 20% 40% 35% 35%


West Coast, Alps and Foothills, Inland Otago, Southland:
Above average summer temperatures are likely. Seasonal rainfall totals are likely to be below normal. Soil moisture levels and river flows are likely to be near normal or below normal, for the summer period as a whole.
Probabilities are assigned in three categories; above average, near average, and below average. The full probability breakdown is:

Temperature Rainfall Soil moisture River flows
Above average 50% 15% 20% 15%
Near average 40% 35% 40% 40%
Below average 10% 50% 40% 45%

Coastal Canterbury, East Otago:
Summer temperatures are likely to be near average or above average. Seasonal rainfall totals are equally likely to be near normal or below normal. Soil moisture levels and river flows are likely to be in the normal range, for the three month season as a whole.

Probabilities are assigned in three categories; above average, near average, and below average. The full probability breakdown is:

Temperature Rainfall Soil moisture River flows
Above average 40% 20% 25% 25%
Near average 40% 40% 45% 45%
Below average 20% 40% 30% 30%