Seasonal Climate Outlook: May - July 2013

Mild early winter on the cards.

The equatorial Pacific Ocean remains in a neutral state (neither El Niño nor La Niña). International guidance indicates that neutral conditions are likely to continue over the next three months (May – July). In the New Zealand region higher pressures than normal are forecast south of the country extending towards the east of the Chathams Islands, while lower pressures than normal are expected to the north of New Zealand. This pattern is expected to be associated with weaker than normal westerly flow.

Temperatures for early winter 2013 (May – July) are very likely to be above average across the entire country. Nevertheless from time to time, cold snaps along with frosts in some areas are still expected as is typical of early winter.  Sea surface temperatures around New Zealand are also forecast to remain above normal over the coming three months.

Rainfall for the May – July period as a whole is likely to be in the near normal range for all regions. Soil moisture levels and river flows are also likely to be in the near normal range for all regions for the coming three months.

Overall picture

Rainfall, soil moisture and river flows

Rainfall totals over the May – July period as a whole are likely to be in the near normal range for all regions. Soil moisture levels and river flows are also likely to be in the near normal range for all regions for the coming three months.

Temperature

May to July temperatures are very likely to be above average across the entire country. Sea surface temperatures around New Zealand are also forecast to remain above normal over the coming three months.

Regional predictions for the next three months

Northland, Auckland, Waikato, Bay of Plenty

Temperatures for May – July are very likely to be above average.  Rainfall totals during this period are likely to be in the near normal range.  Seasonal soil moisture levels and river 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

River flows

Above average

65

30

25

20

Near average

25

50

50

50

Below average

10

20

25

30

Click here to view the historic rainfall and temperature for this region

 

Central North Island, Taranaki, Wanganui, Manawatu, Wellington

Early winter (May – July) temperatures are very likely to be in the above average range.  Seasonal rainfall totals are very likely to be in the near normal range.  Seasonal 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

60

30

30

25

Near average

30

60

50

55

Below average

10

10

20

20

Click here to view the historic rainfall and temperature for this region

 

Gisborne, Hawke’s Bay, Wairarapa

Seasonal temperatures are very likely to be above average.  May – July rainfall totals are likely to be near normal.  Seasonal 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

60

30

25

25

Near average

30

50

45

45

Below average

10

20

30

30

Click here to view the historic rainfall and temperature for this region


Nelson, Marlborough, Buller

May – July temperatures are very likely to be above average.  Seasonal rainfall totals are likely to be in the normal range. Soil moisture levels and river flows 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

River flows

Above average

60

30

30

30

Near average

30

50

50

50

Below average

10

20

20

20

Click here to view the historic rainfall and temperature for this region

 

West Coast, Alps and foothills, inland Otago, Southland

May – July temperatures are very likely to be above average.  Seasonal rainfall totals are very likely to be in the near normal range. Early winter soil moisture and river flows are likely to be at near normal levels, for the season 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

60

20

20

15

Near average

30

60

45

50

Below average

10

20

35

35

Click here to view the historic rainfall and temperature for this region

 

Coastal Canterbury, east Otago

May – July temperatures are very likely to be above average.  Seasonal rainfall totals, soil moisture levels, and river flows are all 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

60

30

30

30

Near average

30

40

40

40

Below average

10

30

30

30

Click here to view the historic rainfall and temperature for this region

 

Background

Atmospheric indicators of ENSO, such as the Southern Oscillation Index (SOI), trade winds, and tropical cloud patterns are close to normal for this time of the year. The estimated NIWA SOI for April was 0.4, and the 3-month February-April estimate was 0.3.  Tropical Pacific Ocean temperatures remained slighly higher than normal in April but are well within the ENSO-neutral range. Climate models indicate that ENSO neutral conditions are likely to continue through the southern hemisphere winter.

There is a very good agreement between the dynamical and statistical models that NIWA uses to establish the seasonal forecast in predicting higher than normal temperatures for May- July. We therefore indicated a high likelihood of above average temperatures for the coming season (above 60 % chance for all regions).

For comment, please contact

Dr Brett Mullan, NIWA Principal Scientist, Climate Variability & Change
Tel (04) 386 0508, Mobile (027) 294 1169

Mr. Darren King, Climate Scientist
Tel (09) 375 2086, Mobile (021) 399 637

 

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.

Click here to visit our media centre