NIWA has published its climate outlook for the next three months:
“A typical La Niña summer likely”
A moderate to strong La Niña, which is currently active in the tropical Pacific region, is expected to persist through summer, according to NIWA. Further, these conditions look likely to persist through to autumn 2011, after which they will ease.
Temperatures for summer (Dec-Feb) are likely ot be at, or above, average throughout New Zealand.
Seasonal rainfall is likely to be below normal in the western South Island, normal or below normal in the north of the South Island, normal or above normal in the north and east of the North Island, and normal elsewhere. On average, La Niña summers tend to exhibit a gradient in rainfall in the north and east of the North Island, tending to be wetter in eastern Northland, coastal Bay of Plenty and Gisborne, and drier farther south and inland. Although rainfall is likely to be normal or above normal in the north and east of the North Island, summer soil moisture levels and river flows are likely to be normal or below normal in those regions, because of the already dry conditions. River flows and soil moisture levels are very likely to be below normal in the west and south of the South Island, and are likely to be near normal or below normal in all other regions, according to the National Climate Centre’s latest seasonal outlook.
The seasonal outlook states that mean sea level pressures are likely to be above normal over New Zealand and to the south of the country, for the three months as a whole.
Tropical cyclone activity is likely to be near- or above-normal this season (through to May 2011). The risk of an ex-tropical cyclone passing close to New Zealand is slightly above 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:
On average for summer (December-February), temperatures are likely to be near or above average in all districts. Sea surface temperatures are presently below normal on average around New Zealand, but are expected to warm to near normal over the summer.
Rainfall, soil moisture, and river flows:
Seasonal rainfall is likely to be below normal in the western South Island, normal or below normal in the north of the South Island, normal or above normal in the north and east of the North Island, and normal elsewhere. Summer soil moisture levels and river flows are very likely to be below normal in the west and south of the South Island, and are likely to be near normal or below normal in all other regions, according to the National Climate Centre’s latest seasonal outlook.
Regional predictions for the next three months:
Northland, Auckland, Waikato, Bay of Plenty:
Temperatures are equally likely to be near average or above average. Seasonal rainfall is equally likely to be near normal or above normal, while soil moisture levels and river flows are equally likely to be below normal or near normal.
Central North Island, Taranaki, Wanganui, Manawatu and Wellington:
Temperatures are equally likely to be near average or above average over summer. Seasonal rainfall totals are likely to be near normal. Seasonal soil moisture levels and river flows are likely to be in the near normal or below normal range.
Gisborne, Hawke’s Bay, Wairarapa:
Temperatures are likely to be near average. Seasonal rainfall totals are equally likely to be in the near normal or above normal range, while soil moisture levels and river flows are likely to be the reverse (near normal or below normal).
Nelson, Marlborough, Buller:
Temperatures are equally likely to be in the near average or above average range. Seasonal rainfall, soil moisture levels, and river flows are likely to be in the below normal or near normal range.
West Coast, Alps and Foothills, Inland Otago, Southland:
Temperatures are likely to be above average, for the three months as a whole. Seasonal rainfall is likely to be below normal. Soil moisture levels and river flows are very likely to be below normal.
Coastal Canterbury, East Otago:
Temperatures are equally likely to be in the near average or above average range. Seasonal rainfall is likely to be near normal. Soil moisture levels and river flows are equally likely to be in the normal or below normal range.