Seasonal Climate Outlook: February - April 2012
Wednesday 1 February 2012, 6:28PM
By NIWA
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LA NINA SET TO FADE WITH A NEAR-NORMAL LEAD-IN TO AUTUMN
The NIWA National Climate Centre’s outlook for early Autumn, February to April 2012, indicates that seasonal rainfalls and temperatures are likely to be near normal for almost all regions, apart from the west and south of the South Island where rainfall is likely to be normal or below normal and temperatures are likely to be average or above average.
Soil moisture levels and river flows are both predicted to follow the same regional pattern to rainfall: likely to be near normal for almost all regions, but normal or below normal for the west and south of the South Island.
A moderate La Niña is in place in the tropical Pacific and should persist into early autumn 2012, according to the NIWA National Climate Centre, before fading back to neutral conditions.
For the February to April season, mean sea level pressures for early autumn (Feb-Apr) are likely to be above average south and southeast of the country, but below average to the north of New Zealand.
For the remainder of the tropical cyclone season through to May, around the normal number of cyclones is expected overall (January to March is typically the most active part of the cyclone season). 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 February-April period as a whole, air temperatures are likely to be near average in most regions, but near average or above average in the west and south of the South Island. Sea surface temperatures in the New Zealand region are likely to be near average.
Rainfall, soil moisture, and river flows:
The National Climate Centre projects that early autumn rainfall totals, soil moisture levels, and river flows are all likely to be near normal throughout most of the country. The exception is the west and south of the South Island where normal or below normal conditions are likely.
Regional predictions for the next three months:
Northland, Auckland, Waikato, Bay of Plenty:
Early autumn temperatures are likely to be near average. Seasonal rainfall totals, soil moisture levels, and river flows are all likely to be near 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 | 30% | 30% | 35% | 35% |
| Near average | 50% | 50% | 45% | 45% |
| Below average | 20% | 20% | 20% | 20% |
Central North Island, Taranaki, Wanganui, Manawatu and Wellington:
Seasonal temperatures are likely to be near average. Early autumn rainfall totals, soil moisture levels, and river flows are likely to be near 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 | 30% | 20% | 30% | 30% |
| Near average | 50% | 50% | 40% | 40% |
| Below average | 20% | 30% | 30% | 30% |
Gisborne, Hawke’s Bay, Wairarapa:
Late summer temperatures are likely to be near average. Seasonal rainfall totals, soil moisture levels, and river flows are all likely to be near 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 | 20% | 30% | 35% | 35% |
| Near average | 50% | 50% | 45% | 45% |
| Below average | 30% | 20% | 20% | 20% |
Nelson, Marlborough, Buller:
Temperatures over the early autumn period are likely to be near average. Seasonal rainfall totals, soil moisture levels and river flows are likely to be near normal for the time of year.
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 | 25% | 30% | 35% | 30% |
| Near average | 50% | 50% | 45% | 50% |
| Below average | 25% | 20% | 20% | 20% |
West Coast, Alps and Foothills, Inland Otago, Southland:
Early autumn temperatures are equally likely to be near average or above average. Seasonal rainfall totals, soil moisture levels and river flows are all equally 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% | 20% | 20% |
| Near average | 40% | 40% | 40% | 40% |
| Below average | 20% | 40% | 40% | 40% |
Coastal Canterbury, East Otago:
Early autumn temperatures are likely to be average. Seasonal rainfall totals, soil moisture levels and river flows are likely to be near 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 | 20% | 30% | 25% | 20% |
| Near average | 50% | 50% | 50% | 50% |
| Below average | 30% | 20% | 25% | 30% |
Background
The tropical Pacific is currently in moderate La Niña conditions, and the ocean now appears to be fully coupled with the tropical atmosphere. Global climate models predict a continuation of La Niña conditions through March 2012, followed by an easing to neutral conditions by early winter.