Seasonal Climate Outlook: May - July 2012
La Niña over, and a mild start to winter for New Zealand.
Neutral conditions prevail in the tropical Pacific (no La Niña or El Niño), after the end of the 2011/12 La Niña event. Near New Zealand, lower than normal pressures are expected to the north of the country, with higher than normal pressures over southern New Zealand
The NIWA National Climate Centre’s outlook for early winter, May to July 2012, indicates air temperatures are likely to be average or above average over most of the country, except for near average in the east of the South Island. Seas around New Zealand are likely to remain near normal or slightly cooler than normal during early winter.
Early winter rainfall is likely to be normal or above normal in the north and east of the North Island, and near normal in other regions. Similarly, soil moisture levels are likely to be normal or above normal in the north and east of the North Island and near normal in other regions. However, river flows are likely to be normal or above normal in the north and east of the North Island, normal or below normal in the west of both islands, and near normal in the north and east of the South Island.
Overall picture
Temperature
Seasonal temperatures are likely to be average or above average over most of the country, except for near average in the east of the South Island. Despite the overall pattern of near or above average temperatures, frosts typical of winter will occur from time to time.
Rainfall, soil moisture and river flows
Early winter rainfall is likely to be normal or above normal in the north and east of the North Island, and near normal in other regions. Soil moisture levels are likely to be normal or above normal in the north and east of the North Island and near normal in other regions. River flows are likely to be normal or above normal in the north and east of the North Island, normal or below normal in the west of both islands, and near normal in the north and east of the South Island.
Regional predictions for the next three months
Northland, Auckland, Waikato, Bay of Plenty
Early winter temperatures are equally likely to be near average or above average. Seasonal rainfall totals, soil moisture levels, and river flows are all equally likely to be in the near normal or above 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 |
40% |
40% |
40% |
40% |
|
Near average |
40% |
40% |
40% |
40% |
|
Below average |
20% |
20% |
20% |
20% |
Click these links to view the historic rainfall and temperature ranges for this region
Central North Island, Taranaki, Wanganui, Manawatu, Wellington
Seasonal temperatures are equally likely to be near average or above average. Early winter rainfall totals and soil moisture levels are likely to be near normal for the three month season as a whole, while river flows are likely to be near normal or below normal.
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% |
20% |
|
Near average |
40% |
50% |
45% |
40% |
|
Below average |
20% |
30% |
35% |
40% |
Click these links to view the historic rainfall and temperature ranges for this region
Gisborne, Hawke’s Bay, Wairarapa
Seasonal temperatures are equally likely to be in the near average or above average range. Early winter rainfall totals, soil moisture levels and river flows are all equally likely to be in the near normal or above 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 |
40% |
40% |
40% |
40% |
|
Near average |
40% |
40% |
40% |
40% |
|
Below average |
20% |
20% |
20% |
20% |
Click these links to view the historic rainfall and temperature ranges for this region
Nelson, Marlborough, Buller
Early winter temperatures are equally likely to be near average or above average. Seasonal rainfall totals, river flows, and soil moisture levels 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 |
40% |
20% |
20% |
20% |
|
Near average |
40% |
50% |
45% |
45% |
|
Below average |
20% |
30% |
35% |
35% |
Click these links to view the historic rainfall and temperature ranges for this region
West Coast, Alps and foothills, inland Otago, Southland
Early winter temperatures are equally likely to be near average or above average. Seasonal rainfall totals and soil moisture levels are likely to be in the near normal range, while river flows are equally likely to be in the near 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 |
River flows |
|
Above average |
40% |
20% |
20% |
20% |
|
Near average |
40% |
50% |
50% |
40% |
|
Below average |
20% |
30% |
30% |
40% |
Click these links to view the historic rainfall and temperature ranges for this region
Coastal Canterbury, east Otago
Seasonal temperatures are likely to be near average. Early winter rainfall totals, river flows, and soil moisture levels 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 |
River flows |
|
Above average |
30% |
30% |
25% |
25% |
|
Near average |
50% |
50% |
50% |
50% |
|
Below average |
20% |
20% |
25% |
25% |
Click these links to view the historic rainfall and temperature ranges for this region
Background
The 2011/12 La Niña event ended during April, and present conditions in the tropical Pacific are ENSO-neutral (no La Niña or El Niño). The three-month average of the Southern Oscillation Index (SOI) for February-April is close to zero. Sea surface temperatures are now warmer than normal in the eastern tropical Pacific.
Almost all global climate models predict neutral conditions in the tropical Pacific over early winter (May-July), with about half of them continuing this situation over the subsequent three months. However, about half the models predict the evolution of an El Niño state during the August-October period. NIWA will continue to monitor the global climate situation.
In spite of the collapse of La Niña in the tropical Pacific, the easterly circulation regime that has been dominating New Zealand climate patterns since December 2011 is expected to persist through the May to July 2012 period.
For comment, please contact
Dr James Renwick, NIWA Principal Scientist, Climate Variability & Change
Tel (021) 178 5550 (mobile), (04) 386 0343 (office DDI)
Dr Brett Mullan, NIWA Principal Scientist, Climate Variability & Change
Tel (04) 386 0508 (office DDI), Mobile (027) 294 1169
Notes to reporters and 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 per cent
- Near average: 30 per cent
- Below average: 10 per cent
We therefore concluded that above average temperatures were very likely.
4. This three-way probability means that a random choice would be correct only 33 per cent (or one-third) of the time. It would be like randomly throwing a dart at a board divided into three 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 per cent 'hit rate' is substantially better than guesswork, 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 US 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 online and is sent to about 3500 recipients of NIWA's newsletters, including many farmers. See www.niwa.co.nz/our-science/climate/publications/all/cu
7. All outlooks are for the three months as a whole. There will inevitably be wet and dry days, and 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 for the long-term mean, whereas for rainfall the "near normal" category lies between approximately 80 per cent and 115 per cent 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.
