Moderate El Niño conditions, but muted influence on New Zealand in the coming season.
An El Niño is now at moderate strength across the equatorial Pacific, and is likely to persist through summer. It is not expected to have a strong influence on New Zealand climate in the coming 3 months, according to the latest outlook from NIWA’s National Climate Centre.
The Centre says rainfall is likely to be in the normal range in many regions, but normal or below normal conditions are likely for the north and east of the North Island, averaged over the November-December-January season as a whole.
Temperatures for the coming 3-month period (November, December, and January combined) are likely to be near average for the North Island and Nelson/Marlborough, but are likely to be in the average or below average ranges for the rest of the South Island.
River flows and soil moisture are likely to be normal or below normal in all regions.
Overall Picture
Temperature:
Air temperatures are likely to be near average over the North Island and northern South Island, and average or below average over the rest of the South Island. Sea surface temperatures near New Zealand are expected to be somewhat below average during November–January. Rainfall, soil moisture, and stream flows: Rainfall is likely to be normal or below normal in the north and east of the North Island, and near normal elsewhere. Rivers flows and soil moisture are likely to be normal or below normal in all 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, soil moisture levels and stream flows are expected to be in the 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 | 20% | 20% | 20% | 20% |
| Near average | 50% | 40% | 40% | 40% |
| Below average | 30% | 40% | 40% | 40% |
Central North Island, Taranaki, Wanganui, Manawatu and Wellington
Seasonal temperatures are projected to be in the near average category. Three-month rainfall totals, soil moisture levels and stream flows, 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% | 20% | 20% | 20% |
| Near average | 50% | 50% | 50% | 50% |
| Below average | 30% | 30% | 30% | 30% |
Gisborne, Hawke’s Bay, Wairarapa:
Three-month temperatures are likely to be in the near average category. Seasonal rainfall totals, soil moisture levels, and stream flows are expected to be in the normal or 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 | 20% | 20% | 20% | 20% |
| Near average | 50% | 40% | 40% | 40% |
| Below average | 30% | 40% | 40% | 40% |
Nelson, Marlborough, Buller:
Temperatures are likely to be in the near average category. November-January rainfall, soil moisture levels and stream flows are likely to be in the 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 | 20% | 20% | 20% | 20% |
| Near average | 50% | 50% | 50% | 50% |
| Below average | 30% | 30% | 30% | 30% |
West Coast, Alps and Foothills, Inland Otago, Southland:
Temperatures are likely to be in the below average category. Seasonal rainfall, soil moisture levels and stream flows are projected to be in the 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 | 20% | 30% | 30% | 30% |
| Near average | 30% | 50% | 50% | 50% |
| Below average | 50% | 20% | 20% | 20% |
Coastal Canterbury, East Otago:
Temperatures are equally likely to be in the near average or below average categories. Seasonal rainfall is expected to be in the normal range, while soil moisture levels and stream flows are likely to be normal or 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% | 20% |
| Near average | 40% | 50% | 40% | 40% |
| Below average | 40% | 30% | 40% | 40% |
Background
A moderate El Niño is present in the equatorial Pacific Ocean, and is expected to persist through to the autumn of 2010. Most of the El Niño forecast models predict El Niño persisting to the end of summer, with some strengthening a little between now and the end of the year.
El Niño events can lead to dry conditions in eastern parts of New Zealand over the spring and summer seasons. Consistent with this picture, the latest guidance suggests that November 2009-January 2010 rainfall is likely to be in the normal or below normal range for the north and east of the North Island.
For comment, please contact:
Dr James Renwick, NIWA Principle Scientist, Climate Variability & Change
Tel mobile (021) 178 5550, office DDI (04) 386 0343
Dr Andrew Tait, Climate Scientist
Tel (04) 386 0562 (office DDI), mobile (027) 327 7948
© Copyright NIWA 2009. All rights reserved. Acknowledgement of NIWA as the source is required.
Notes to reporters & editors
- 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.
- 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.
- 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%
- 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.
- 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).
- 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
- 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.
- 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.