A cold June expected, but a near-normal winter as a whole in most regions.
Another cold month lies ahead, with below average temperatures likely in many regions, according to the latest outlook from NIWA’s National Climate Centre.
Despite the cold start to winter, however, the centre says temperatures for the season as a whole (June, July, and August combined) are likely to be about average, except for Canterbury and eastern Otago where average or below average temperatures are expected.
While this is the overall expectation, it does not rule out cold spells typical of winter. The centre is also anticipating more frosts than usual for the South Island and central North Island.
Rainfall is likely to be normal or above normal over the north and east of the North Island, and normal elsewhere except for normal or below normal in the west of the South Island.
The centre says that normal or above normal soil moisture levels are likely in most regions. With regard to stream flows, normal or above normal conditions are likely in the northern North Island and the east of the South Island. Normal or below normal stream flows are expected in the west and south of the South Island, and normal stream flows elsewhere.
Mean sea level pressures are likely to be lower than normal to the north of the country during winter, with an easterly or south-easterly wind flow anomaly over New Zealand.
Overall Picture
Temperature
Temperatures are expected to be near average in most regions, but average or below average in the east of the South Island. Sea surface temperatures around New Zealand are expected to be average or below average through the June-August period.
Rainfall, soil moisture, and stream flows:
Rainfal l is likely to be normal or above normal over the north and east of the North Island, normal or below normal in the west of the South Island, and normal elsewhere. Normal or above normal soil moisture levels are likely in most locations. Stream flows are also likely to be normal or above normal in the northern North Island and the east of the South Island. Normal or below normal stream flows are expected in the west and south of the South Island, and normal stream flows are likely elsewhere.
Regional predictions for the next three months
Northland, Auckland, Waikato, Bay of Plenty
Average temperatures are likely. Normal or above normal rainfall, soil moisture and stream flows are likely.
Probabilities are assigned in three categories; above average, average, and below average. The full probability breakdown is:
|
Temperature |
Rainfall |
Soil moisture |
Stream flows |
|
|---|---|---|---|---|
|
Above normal |
30 % |
40 % |
40 % |
40 % |
|
Normal |
50 % |
40 % |
40 % |
40 % |
|
Below normal |
20 % |
20 % |
20 % |
20 % |
Central North Island, Taranaki, Wanganui, Manawatu and Wellington:
Average temperatures are likely. Normal rainfall and stream flows are likely, with soil moisture expected to be normal or above normal.
Probabilities are assigned in three categories; above average, average, and below average. The full probability breakdown is:
|
Temperature |
Rainfall |
Soil moisture |
Stream flows |
|
|---|---|---|---|---|
|
Above normal |
30 % |
30 % |
40 % |
30 % |
|
Normal |
50 % |
50 % |
40 % |
50 % |
|
Below normal |
20% |
20 % |
20 % |
20 % |
Gisborne, Hawke’s Bay, Wairarapa:
Near average temperatures are likely for the three months. Rainfall is expected to be normal or above normal. Soil moisture and stream flows are likely to be normal for the season as a whole.
Probabilities are assigned in three categories; above average, average, and below average. The full probability breakdown is:
|
Temperature |
Rainfall |
Soil moisture |
Stream flows |
|
|---|---|---|---|---|
|
Above normal |
30 % |
40 % |
30 % |
30 % |
|
Normal |
50 % |
40 % |
40 % |
40 % |
|
Below normal |
20 % |
20 % |
30 % |
30 % |
Nelson, Marlborough, Buller:
Average temperatures are likely, with near normal rainfall, soil moisture and stream flows.
Probabilities are assigned in three categories; above average, average, and below average. The full probability breakdown is:
|
Temperature |
Rainfall |
Soil moisture |
Stream flows |
|
|---|---|---|---|---|
|
Above normal |
30 % |
30 % |
30 % |
20 % |
|
Normal |
50 % |
50 % |
40 % |
50 % |
|
Below normal |
20 % |
20 % |
30 % |
30 % |
West Coast, Alps and Foothills, Inland Otago, Southland:
Average temperatures are likely. Rainfall is likely to be normal or below normal, as are stream flows. Soil moisture is expected to be near normal over the season.
Probabilities are assigned in three categories; above average, average, and below average. The full probability breakdown is:
|
Temperature |
Rainfall |
Soil moisture |
Stream flows |
|
|---|---|---|---|---|
|
Above normal |
30 % |
20 % |
30 % |
20 % |
|
Normal |
50 % |
40 % |
40 % |
40 % |
|
Below normal |
20 % |
40 % |
30 % |
40 % |
Coastal Canterbury, East Otago:
Average or below average temperatures are likely. Near normal rainfall is expected for the three month period as a whole. Soil moisture and stream flows are likely to be normal or above normal.
Probabilities are assigned in three categories; above average, average, and below average. The full probability breakdown is:
|
Temperature |
Rainfall |
Soil moisture |
Stream flows |
|
|---|---|---|---|---|
|
Above normal |
20 % |
35 % |
40 % |
40 % |
|
Normal |
40 % |
50 % |
40 % |
40 % |
|
Below normal |
40 % |
15 % |
20 % |
20 % |
Background
In the New Zealand region, mean sea level pressures are likely to be lower than normal to the north of the country during winter, with an easterly or south-easterly air flow anomaly over New Zealand. Sea surface temperatures around New Zealand are expected to be average or below average through the winter period.
The recent La Niña is clearly over and the Equatorial Pacific is currently in a neutral state, and expected to stay that way over winter. However, equatorial sea surface temperatures in the Pacific have increased rapidly over the past two months, and forecast models predict an increasing chance of a transition to El Niño conditions during spring. NIWA will monitor the situation closely over the winter months.
For comment, please contact:
Dr James Renwick, NIWA Principal Scientist, Climate Variability & Change
Tel (04) 386 0343 (office DDI), mobile (021) 178 5550
Dr Brett Mullan, NIWA Principal Scientist, Climate Variability & Change
Tel (04) 386 0508 (office DDI)
© 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.