Seasonal Climate Outlook: June - August 2013

Mild winter very likely.

The equatorial Pacific Ocean remains in a neutral state (neither El Niño nor La Niña). International guidance indicates that these neutral conditions are likely to persist over the coming three months (June–August). In the New Zealand region higher than normal pressures are forecast south and southeast of the country, whereas lower than normal pressures are expected to the west and north of New Zealand. This circulation pattern is expected to be associated with more northerly and northeasterly airflow than usual, for the season as a whole.

Overall, temperatures for winter 2013 (June – August) are very likely to be above average across the entire country. However, occurrences of cold snaps, frost and snow conditions should, of course, still be expected in many areas from time to time, as is typical of winter. Sea surface temperatures around New Zealand’s coasts are also forecast to be above the climatological average for the coming three months.

Winter rainfall is likely to be in the normal or above normal ranges in the north and east of the North Island, and in the near normal range for the remainder of the country. Soil moisture levels and river flows are likely to be above normal in the north of the North Island, normal or above normal in the east of the South Island, normal or below normal in the west and south of the South Island, and near normal in other regions.

Overall picture

Rainfall, soil moisture and river flows

Rainfall for the June–August period as a whole is likely to be in the normal or above normal ranges in the north and east of the North Island, and near normal for the southwest of the North Island and for all the South Island. Soil moisture levels and river flows are likely to be above normal in the north of the North Island, and normal or above normal in the east of the South Island. Elsewhere, soil moisture levels and river flows are likely to be near normal, except in the west and south of the South Island where normal or below normal conditions are likely.

Temperature

June to August 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 the June – August period as a whole are very likely to be above average.  Rainfall totals during this period are likely to be in the near normal or above normal ranges.  Seasonal soil moisture levels and river flows are likely to be in the 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

65

40

45

45

Near average

25

40

35

35

Below average

10

20

20

20

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


Central North Island, Taranaki, Wanganui, Manawatu, Wellington

Winter (June – August) temperatures are very likely to be in the above average range.  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

35

30

30

Near average

30

45

45

45

Below average

10

20

25

25

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

 

Gisborne, Hawke’s Bay, Wairarapa

Winter temperatures are very likely to be above average.  June – August rainfall totals are likely to be near normal or above 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

40

30

30

Near average

30

40

45

45

Below average

10

20

25

25

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

 


Nelson, Marlborough, Buller

Winter temperatures are very likely to be above average.  Seasonal rainfall totals, 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

60

35

30

30

Near average

30

45

45

45

Below average

10

20

25

25

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

 

West Coast, Alps and foothills, inland Otago, Southland

June – August temperatures are very likely to be above average.  Winter rainfall totals are likely to be in the near normal range. Soil moisture and river flows are likely to be at near normal or below 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

35

25

25

Near average

30

45

40

40

Below average

10

20

35

35

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

 

Coastal Canterbury, east Otago

June – August temperatures are very likely to be above average.  Winter rainfall totals are likely to be in the near normal range. Soil moisture levels and river flows are likely to be at near normal or above 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

30

35

35

Near average

30

40

40

40

Below average

10

30

25

25

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 May was 0.7, and the 3-month March-May estimate was 0.6.  Ocean surface temperatures are slightly lower than normal in eastern tropical Pacific but still 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 June-August. We therefore indicated a high likelihood of above average New Zealand temperatures for the coming winter season (60 % chance or above for all regions).

 

For comment, please contact

Dr Brett Mullan
Principal Scientist, Climate Variability & Change
Tel (04) 386 0508

Dr Nicolas Fauchereau
Climate Scientist
Tel (09) 375 2053

 

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.

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