Seasonal Climate Outlook: January - March 2010

Late summer – more of the same.

The current El Niño is well-established in the equatorial Pacific, and is likely to persist at moderate intensity through the rest of summer, before weakening during the autumn. Scientists at NIWA’s National Climate Centre say that spells more of the same over the next three months: similar conditions to those experienced in December, for most of the country.
According to the centre’s latest outlook, mean sea level pressures are likely to continue to be higher than normal to the north of the country and lower than normal to the south, resulting in stronger than normal westerlies over New Zealand. Current dry soil conditions are likely to continue in the north and east of the North Island, and in much of the eastern South Island, where below normal stream flows and soil moisture levels are likely through to March. The centre says late summer (January to March) rainfall totals are likely to be in the below normal range in the north and east of the North Island, normal or below normal in Nelson-Marlborough, and in the normal range in other regions. Temperatures are likely to be average or below average in all regions, for the 3-month period (January, February and March) as a whole. There will, of course, still be warm spells at times, especially in eastern regions in north-westerly wind conditions. Rivers flows and soil moistures are likely to be below normal in the north and east of both Islands, but in the normal range in western regions.

 

Overall Picture 

Temperature:

Air temperatures are likely to be average or below average in all regions. Sea surface temperatures are expected to be below average around and east of the South Island, but near normal to the north of New Zealand.

Rainfall, soil moisture, and stream flows:


Rainfall is likely to be below normal in the north and east of the North Island, normal or below normal in the northern South Island, and near normal elsewhere. Below normal soil moistures and river flows are likely in the north and east of both Islands, with near-normal soil moistures and river flows likely in western regions.

Regional predictions for the next three months:

Northland, Auckland, Waikato, Bay of Plenty:

Temperatures are likely to be in the near average category.  Seasonal (3-month) rainfall totals are likely to be below normal, while river flows and soil moisture levels are very likely to be in the 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 15% 15% 10% 10%
Near average 50% 30% 30% 30%
Below average 35% 55% 60% 60%

Central North Island, Taranaki, Wanganui, Manawatu and Wellington

Seasonal temperatures are likely to be in the average or below average category. January-March rainfall totals, stream flows and soil moisture levels 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 20% 20% 20% 20%
Near average 40% 50% 50% 50%
Below average 40% 30% 30% 30%

Gisborne, Hawke’s Bay, Wairarapa:

Temperatures averaged over the three months are likely to be in the near average category. Seasonal rainfall totals are likely to be below normal, while stream flows and soil moisture levels are very likely to be in the below normal range.

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 30% 15% 10% 10%
Near average 50% 30% 30% 30%
Below average 20% 55% 60% 60%

Nelson, Marlborough, Buller:

Seasonal temperatures are likely to be near average or below average levels. Rainfalls are likely to be normal or below normal, with below normal rainfalls more likely in the east of the region.  Stream flows and soil moisture levels are likely to be 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 20% 20% 10% 10%
Near average 40% 40% 40% 40%
Below average 40% 40% 50% 50%

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

Temperatures are likely to be in the average or below average category. Seasonal rainfall, stream flows and soil moisture levels are expected 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 20% 30% 30% 30%
Near average 40% 50% 50% 50%
Below average 40% 20% 20% 20%

Coastal Canterbury, East Otago:

Temperatures are most likely to be in the near average category. Seasonal rainfall is expected to be in the normal range, while soil moisture levels and stream flows are most likely to be below 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 20% 20% 20% 15%
Near average 50% 50% 35% 35%
Below average 30% 30% 45% 50%

Background

El Niño events can often lead to dry conditions in eastern and northern parts of New Zealand over the summer season. Soil moistures are already very low at the start of January through most of the north and east of the North Island, and the eastern South Island. Conditions have been particularly dry lately in Northland, the Bay of Plenty, and Central Otago.  The latest guidance suggests that drier conditions are likely in the north and east of both islands over the January-March 2010 period. El Niño events are also often associated with cooler than average conditions in the New Zealand region, consistent with the latest outlook.

For comment, please contact:

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

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

Dr Brett Mullan, NIWA Principal Scientist, Climate Variability & Change

Tel (04) 386 0508 (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.