Seasonal Climate Outlook: April - June 2011
Mild conditions continuing into late autumn as La Niña weakens.
The La Niña event continues in the tropical Pacific, but is weakening, says the NIWA National Climate Centre. Neutral conditions are expected in the tropical Pacific by the beginning of winter.
Late autumn (April to June) temperatures are likely to be average or above average in the east of the South Island, and above average in all other regions.
Seasonal rainfall is likely to be normal or above normal in the north and east of the North Island, normal or below normal in the east of the South Island, and near normal elsewhere. Soil moisture levels and river flows are expected to have a similar regional pattern to the rainfall.
The seasonal outlook states that mean sea level pressures are likely to be below normal to the north of New Zealand and above normal to the east and south of the country, with weaker than normal westerlies across New Zealand.
Tropical cyclone activity is likely to be near- or above-normal for the rest of this cyclone season (through to May).
Overall Picture
Temperature:
On average for late autumn, temperatures are likely to be average or above average in the east of the South Island, and above average in all other regions. Sea surface temperatures near New Zealand are expected to remain above average, especially to the east of the North Island.
Rainfall, soil moisture, and river flows:
The National Climate Centre says that seasonal rainfall is likely to be normal or above normal in northern and eastern North Island regions, normal or below normal in the eastern South Island, and near normal elsewhere. River flows are likely to be normal or above normal in the north of the North Island, normal or below normal in the east of the South Island, and near normal elsewhere. Soil moisture levels are likely to be normal or above normal in the north and east of the North Island, normal or below normal in the east of the South Island, and near normal elsewhere.
Regional predictions for the next three months:
Northland, Auckland, Waikato, Bay of Plenty:
Temperatures are very likely to be above average for the time of year. Seasonal rainfall totals, soil moisture levels, and river flows over late autumn are equally likely to be in the normal or above normal ranges.
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 | 60% | 40% | 40% | 40% |
| Near average | 30% | 40% | 40% | 40% |
| Below average | 10% | 20% | 20% | 20% |
Click these links to view the historic rainfall and temperature ranges for this region
Central North Island, Taranaki, Wanganui, Manawatu and Wellington:
Temperatures are likely to be above average. Seasonal rainfall totals, soil moisture levels and river flows and all likely to be near normal over April-June.
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 | 50% | 30% | 30% | 30% |
| Near average | 30% | 50% | 50% | 50% |
| Below average | 20% | 20% | 20% | 20% |
Click these links to view the historic rainfall and temperature ranges for this region
Gisborne, Hawke’s Bay, Wairarapa:
Temperatures are likely to be above average. Seasonal rainfall totals and soil moisture levels are equally likely to be in the near normal or above normal range. River flows are likely to be near normal.
Probabilities are assigned in three categories; above normal, near normal, and below normal. The full probability breakdown is:
| Temperature | Rainfall | Soil moisture | River flows | |
|---|---|---|---|---|
| Above average | 50% | 40% | 40% | 35% |
| Near average | 30% | 40% | 40% | 40% |
| Below average | 20% | 20% | 20% | 25% |
Click these links to view the historic rainfall and temperature ranges for this region
Nelson, Marlborough, Buller:
Temperatures are likely to be in the above average range. Seasonal rainfall, soil moisture levels and river flows are likely to be in the near normal range.
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 | 50% | 30% | 25% | 25% |
| Near average | 30% | 50% | 45% | 45% |
| Below average | 20% | 20% | 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 likely to be above average, for the three months as a whole. Seasonal rainfall, soil moisture levels, and river flows are all 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 | River flows | |
|---|---|---|---|---|
| Above average | 50% | 20% | 25% | 20% |
| Near average | 30% | 50% | 45% | 50% |
| Below average | 20% | 30% | 30% | 30% |
Click these links to view the historic rainfall and temperature ranges for this region
Coastal Canterbury, East Otago:
Temperatures are equally likely to be in the near average or above average range. Seasonal rainfall, soil moisture levels, and river flows are all likely to be in the normal range or the below normal range, for the 3-month period 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 | 40% | 20% | 20% | 15% |
| Near average | 40% | 40% | 40% | 40% |
| Below average | 20% | 40% | 40% | 45% |
Click these links to view the historic rainfall and temperature ranges for this region
Background
The tropical Pacific is in a weakening La Niña state, which is expected to have dissipated entirely by the end of the three-month outlook period. In the longer-term beyond June, the majority of the international forecast models maintain neutral conditions in the Pacific, although a few models suggest the development of an El Niño event late in 2011.
For comment, please contact:
Dr James Renwick, NIWA Principal Scientist, Climate Variability & Change
Mobile (021) 178 5550, Tel (04) 386 0343 (office DDI)
Dr Brett Mullan, NIWA Principal Scientist, Climate Variability & Change
Tel (04) 386 0508 (office DDI)
© Copyright NIWA 2011. All rights reserved. Acknowledgement of NIWA as the source is required.
Notes to reporters & editors
1. 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.
2. 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.
3. The outlooks state the probability for above average conditions, near average conditions, and below average conditions for rainfall, temperature, soil moisture, and river flows. For example, for winter (June-July-August) 2007, for all the North Island, we assigned the following probabilities for temperature:
· Above average: 60%
· Near average: 30%
· Below average: 10%
We therefore concluded that above average temperatures were very likely.
4. 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.
5. 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).
6. 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: www.niwascience.co.nz/ncc
7. 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 exact range in temperature and rainfall within each of the three categories varies with location and season. However, as a guide, the “near average” or middle category for the temperature predictions includes deviations up to ±0.5°C from the long-term mean, whereas for rainfall the “near normal” category lies approximately between 80% and 115% of the long-term mean.
8. 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.