Seasonal Climate Outlook: February - April 2013

Return to near normal over the coming season.

The equatorial Pacific Ocean is still in a neutral state (neither El Niño nor La Niña). Global guidance indicates that these neutral conditions are very likely to persist throughout the Southern Hemisphere autumn. For the New Zealand region over the coming three months (February-April 2013), slightly higher than normal pressures are expected to the south of the country and southeast of the Chathams Islands, accompanied with weak anomalous flow from the north-easterly quarter over New Zealand.

February-April rainfall is likely to be near normal everywhere but for the north of the North Island, where near normal or above normal rainfall is likely. Soil moisture levels and river flows are likely to be near normal levels for all of New Zealand for the season as a whole. The return to near normal soil moisture levels will take some time for those parts of Northland, Auckland and the North Island east coast that are currently very much drier than usual.

February-April temperatures are likely to be near average or above average in the north of the North Island, and near average in all other regions. Sea surface temperatures around New Zealand are expected to be near normal over the next three months.

For this tropical cyclone season (November – April), the risk of an ex-Tropical Cyclone approaching New Zealand is expected to be near normal. On average, one ex-Tropical Cyclone nears New Zealand during the season.

Overall picture

Rainfall, soil moisture and river flows

February-April rainfall is likely to be near normal or above normal in the north of the North Island, and near normal elsewhere.

Seasonal soil moisture levels and river flows are likely to be at near normal levels for the whole country.

Temperature

February-April temperatures are likely to be near average or above average in the north of the North Island, and near average in all other regions. Sea surface temperatures around New Zealand are expected to be close to average the coming three months.

Regional predictions for the next three months

Northland, Auckland, Waikato, Bay of Plenty

February-April temperatures are likely to be in the near average or above average range. Rainfall is likely to be in the near normal or above normal range. Soil moisture levels and river flows are likely to be in the near normal range 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

40

35

25

20

Near average

40

40

45

45

Below average

20

25

30

35

Click these links to view the historic rainfall and temperature. 

Central North Island, Taranaki, Wanganui, Manawatu, Wellington

February-April temperatures are likely to be near average. Rainfall, soil moisture levels and river flows are all likely to be in the near normal range 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

40

35

25

20

Near average

40

40

45

45

Below average

20

25

30

35

Click these links to view the historic rainfall and temperature. 

Gisborne, Hawke's Bay, Wairarapa

Seasonal temperatures are likely to be in the near average range. February-April rainfall totals, soil moisture levels and river flows are all likely to be in the near normal range for this time of year.

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

25

30

20

20

Near average

50

40

45

45

Below average

25

30

35

35

Click these links to view the historic rainfall and temperature. 

Nelson, Marlborough, Buller

February-April temperatures are likely to be near average. Seasonal rainfall totals, soil moisture levels, and river flows are also 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

25

30

25

25

Near average

50

40

45

45

Below average

25

30

30

30

Click these links to view the historic rainfall and temperature. 

West Coast, Alps and foothills, inland Otago, Southland

Temperatures are likely to be near average over the next three months. Seasonal rainfall totals are equally likely to be in the near normal range. February-April soil moisture levels and river flows are also likely to be near normal levels.

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

25

30

30

25

Near average

50

40

40

45

Below average

25

30

30

30

Click these links to view the historic rainfall and temperature. 

Coastal Canterbury, east Otago

February-April temperatures are likely to be near average. Seasonal rainfall, 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

25

30

20

20

Near average

50

40

45

45

Below average

25

30

35

35

Click these links to view the historic rainfall and temperature. 

Background

The equatorial Pacific Ocean as a whole reflects ENSO-neutral conditions (neither El Niño nor La Niña), despite slightly cooler than normal sea surface temperatures in the eastern Pacific. The Southern Oscillation Index (SOI) for January was very close to 0 and the 3-month SOI (November 2012 - January 2013) is -0.2.

International guidance indicates a very high likelihood for the tropical Pacific Ocean to remain neutral over the next three months (February-April). All the 10 dynamical models and 5 statistical models monitored by NIWA forecast ENSO-neutral SST anomalies for February-April 2013 and also for the following May-July season.

The rainfall forecasts have a fairly 'flat' distribution (30:40:30 per cent in the terciles of below normal:near normal:above normal). This is a consequence of no strong signal in the global forecast models for the coming season.

For comment, please contact

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

Dr Nicolas Fauchereau, Climate Scientist
Tel (09) 375 2053, Mobile (027) 9348940

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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