Seasonal Climate Outlook: October - December 2010

La Niña intensifies; warm late spring period very likely.

The current La Niña has recently strengthened, says the NIWA National Climate Centre. A moderate to strong La Niña event is presently underway, with further intensification possible this year. La Niña conditions are likely to continue through to at least autumn of 2011.

Late spring (October–December) temperatures are likely to be above average, in all regions.  Rainfall is likely to be near normal or below normal in the east of both islands and the southwest of the South Island, and near normal elsewhere, averaged over the three month period October–December.

Soil moisture levels and stream flows are likely to be near normal or below normal in most regions, except the southwest of the North Island and northern South Island where near normal levels are likely.

The National Climate Centre’s seasonal outlook states that mean sea level pressures are likely to be above normal over and south of New Zealand, for October–December as a whole, with weaker than normal westerly winds.

 


Overall Picture

Temperature:

Temperatures are likely to be above average in the east of both islands and in the north of the South Island, and very likely to be above average in other districts. Sea surface temperatures are presently near normal around New Zealand, but are expected to become warmer than normal around the North Island as the season progresses.

Rainfall, soil moisture, and stream flows:

Seasonal rainfall is likely to be near normal or below normal in the east of both islands and the southwest of the South Island, and near normal elsewhere.  Soil moisture levels and stream flows are likely to be near normal or below normal in most regions, except in the southwest of the North Island and north of the South Island, where they are likely to be near normal.

Regional predictions for the next three months:

Northland, Auckland, Waikato, Bay of Plenty:

Temperatures are very likely to be in the above average range.  Near normal seasonal rainfall is likely, while soil moisture levels and stream 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 Stream flows
Above average 60% 30% 25% 25%
Near average 25% 50% 40% 40%
Below average 15% 20% 35% 35%

Click these links to view the historic rainfall and temperature ranges for this region

 

Central North Island, Taranaki, Wanganui, Manawatu and Wellington:

Temperatures are very likely to be above average for the late spring period.  Seasonal rainfall totals, soil moisture levels and stream 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 Stream flows
Above average 65% 25% 25% 25%
Near average 20% 50% 45% 45%
Below average 15% 25% 30% 30%

Click these links to view the historic rainfall and temperature ranges for this region

 

Gisborne, Hawke’s Bay, Wairarapa:

Above average seasonal temperatures are likely.  Seasonal rainfall totals, soil moisture levels and stream flows are likely to be near normal or below normal. 

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

Temperature Rainfall Soil moisture Stream flows
Above average 50% 20% 25% 15%
Near average 40% 40% 40% 45%
Below average 10% 40% 35% 40%

Click these links to view the historic rainfall and temperature ranges for this region

 

Nelson, Marlborough, Buller:

Temperatures are likely to be above average.  Seasonal rainfall, soil moisture, and stream 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 Stream flows
Above average 50% 35% 25% 20%
Near average 40% 50% 50% 50%
Below average 10% 15% 25% 30%

Click these links to view the historic rainfall and temperature ranges for this region

 

West Coast, Alps and Foothills, Inland Otago, Southland:

Seasonal temperatures are very likely to be above average.  Seasonal rainfall totals, soil moisture and stream flows are equally likely to be in the near normal or below normal range.

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

Temperature Rainfall Soil moisture Stream flows
Above average 65% 20% 20% 20%
Near average 25% 40% 40% 40%
Below average 10% 40% 40% 40%

Click these links to view the historic rainfall and temperature ranges for this region

 

Coastal Canterbury, East Otago:

Temperatures are likely to be in the above average range.  Late spring rainfall totals, soil moisture and stream 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 Stream flows
Above average 45% 20% 20% 20%
Near average 30% 40% 40% 40%
Below average 25% 40% 35% 40%

Click these links to view the historic rainfall and temperature ranges for this region

Background

The tropical Pacific is now exhibiting moderate to strong La Niña conditions, as the current event continues to strengthen. The La Niña state is expected to continue to at least the autumn of 2011.

For comment, please contact:

Dr Brett Mullan, NIWA Principal Scientist

Tel (04) 386 0508 (office DDI), mobile (027) 294 1169

Dr Andrew Tait, NIWA Principal Scientist

Tel (04) 386 0562 (office DDI)

© Copyright NIWA 2010. All rights reserved. Acknowledgement of NIWA as the source is required.

Notes to reporters & editors

  1.    
  2. NIWA’s outlooks indicate the likelihood of    climate conditions being at, above, or below average for the    season as a whole. They are not ‘weather    forecasts’. It is not possible to forecast precise    weather conditions three months ahead of time.   
  3. The outlooks are the result of the expert    judgment of NIWA’s climate scientists. They take into    account observations of atmospheric and ocean conditions and    output from global and local climate models. The presence of El    Niño or La Niña conditions and the sea surface    temperatures around New Zealand can be a useful indicator of    likely overall climate conditions for a season.   
  4. The outlooks state the probability for above    average conditions, average conditions, and below average    conditions for rainfall, temperature, soil moisture, and stream    flows. For example, for winter (June-July-August) 2007, for all    the North Island, we assigned the following probabilities for    temperature:

       
    •        
    • Above average: 60%
    •        
    • Average: 30%
    •        
    • Below average: 10%
    •    
        We therefore conclude that above average temperatures were    very likely.
  5. This three-way probability means that a random    choice would only be correct 33% (or one-third) of the time. It    would be like randomly throwing a dart at a board divided into    3 equal parts, or throwing a dice with three numbers on it. An    analogy with coin tossing (a two-way probability) is not    correct.   
  6. A 50% ‘hit rate’ is substantially    better than guess-work, and comparable with the skill level of    the best overseas climate outlooks. See, for example, analysis    of global outlooks issued by the International Research    Institute for Climate and Society based in the U.S.    (http://iri.ldeo.columbia.edu/) published in the Bulletin of    the American Meteorological Society (Goddard, L., A. G.    Barnston, and S. J. Mason, 2003: Evaluation of the IRI's    “net assessment” seasonal climate forecasts    1997-2001. Bull. Amer. Meteor. Soc., 84,    1761-1781).   
  7. Each month NIWA publishes an analysis of how well    its outlooks perform. This is available on-line and is sent to    about 3,500 recipients of NIWA’s newsletters, including    many farmers. See The Climate Update   
  8. All outlooks are for the three months as a whole.    There will inevitably be wet and dry days, hot and cold days,    within a season.   
  9. The seasonal climate outlooks are an output of a    scientific research programme, supplemented by NIWA’s    Capability Funding. NIWA does not have a government contract to    produce these outlooks.