Seasonal Climate Outlook: November 2010 - January 2011

La Niña locked in – a warm early summer likely.

A moderate to strong La Niña is well-established in the tropical Pacific, and may strengthen further through the rest of 2010, says the NIWA National Climate Centre.  La Niña conditions are likely to continue through to autumn of 2011.

Early summer (November to January) temperatures are likely or very likely to be above average for this time of year across the whole country.

Rainfall is likely to be normal or below normal over the South Island, with below normal soil moisture levels and stream flows likely over much of the South Island. In the North Island, rainfall is likely to be normal or above normal, with above normal soil moisture levels and stream flows in the east, according to the Centre’s latest seasonal outlook.

The National Climate Centre’s seasonal outlook states that mean sea level pressures are likely to be above normal near 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 (November–May). 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:

Averaged over November-January, temperatures are likely or very likely to be above average in all 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 above normal in the north and east of the North Island, near normal over the southwest North Island and the northern South Island, and normal or below normal over the rest of the South Island. Soil moistures and stream flows are likely to be above normal in the east of the North Island, near normal in the western North Island and northern South Island, and below normal over the rest of the South Island.

Regional predictions for the next three months:

Northland, Auckland, Waikato, Bay of Plenty:

Temperatures are very likely to be in the above average range.  Seasonal rainfall is equally likely to be near normal or above normal, while there is no clear guidance for soil moisture levels and stream flows.

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% 40% 35% 35%
Near average 30% 40% 30% 30%
Below average 10% 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 early summer.  Seasonal rainfall totals, soil moisture levels, and stream flows are likely to be near normal overall.

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% 20% 30% 30%
Near average 30% 50% 40% 40%
Below average 10% 30% 30% 30%

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

 

Gisborne, Hawke’s Bay, Wairarapa:

Temperatures are very likely to be in the above average range.  Seasonal rainfall is equally likely to be near normal or above normal, while soil moisture levels and stream flows are likely to be above normal overall. 

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 60% 40% 50% 50%
Near average 30% 40% 30% 30%
Below average 10% 20% 20% 20%

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

 

Nelson, Marlborough, Buller:

Temperatures are very likely to be in the above average range.  Seasonal rainfall, 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 60% 20% 30% 30%
Near average 30% 50% 40% 40%
Below average 10% 30% 30% 30%

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

 

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

Temperatures are very likely to be in the above average range, for the three months as a whole.  Seasonal rainfall is likely to be below normal. Soil moisture levels and stream flows are likely to be below normal or 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 60% 20% 25% 25%
Near average 30% 30% 35% 35%
Below average 10% 50% 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.  Seasonal rainfall is equally likely to be near normal or below normal. Soil moisture levels and stream flows are very likely to be below normal for November-January.

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% 20% 15% 15%
Near average 30% 40% 25% 25%
Below average 20% 40% 60% 60%

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

Background

The tropical Pacific is in a moderate to strong La Niña state, which is likely to continue into early 2011, and may strengthen further through the rest of 2010.

For comment, please contact:

Dr James Rewick, NIWA Principal Scientist, Climate Variability & Change

Tel (04) 386 0343 (office DDI), mobile (021) 178 5550

Georgina Griffiths, NIWA Climate Scientist

Tel (09) 375 4506, mobile (027) 293 6545

© 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.