Seasonal Climate Outlook: August - October 2009

The climate over the next three month period is expected to be typical of early spring right across New Zealand, according to the latest outlook from NIWA’s National Climate Centre.

Following the third cold month in a row, the centre says temperatures for the coming season (August, September, and October combined) are likely to be about average.  Rainfalls are also likely to be near normal in all regions.

Going along with the rainfall expectation, the centre says that near normal soil moisture levels and stream flows are also likely in all regions.

In the New Zealand region over the coming three months, mean sea level pressures are likely to transition towards El Niño-like conditions, with enhanced westerly winds at times.

In this example below, the climate models suggest that below normal conditions are likely (50% chance), but, given the variable nature of the climate, the chance of normal or above normal conditions is also shown (30% and 20% respectively).

Overall Picture

Temperature:

 

Air temperatures are expected to be near average in all regions.  Sea surface temperatures near New Zealand are likely to be somewhat below average through August-October.

Rainfall, soil moisture, and stream flows:

Rainfall, soil moisture levels and stream flows are likely to be near normal in all regions.

 

Regional predictions for the next three months:

Northland, Auckland, Waikato, Bay of Plenty:

Average temperatures are likely. Normal rainfall, soil moisture and stream flows are likely 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 20 % 30 % 30 % 30 %
Normal 50 % 50 % 50 % 50 %
Below normal 30 % 20 % 20 % 20 %

North Island, Taranaki, Wan ganui, Manawatu and Wellington

 

Average temperatures are likely. Normal rainfall, soil moisture and stream flows are likely, averaged over August-October.

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 % 20 % 20 % 20 %
Normal 50 % 50 % 50 % 50 %
Below normal 30% 30 % 30 % 30 %

Gisborne, Hawke’s Bay, Wairarapa:

 

Average temperatures are likely. 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 % 20 % 20 % 20 %
Normal 50 % 50 % 50 % 50 %
Below normal 20 % 30 % 30 % 30 %

Nelson, Marlborough, Buller:

 

Average temperatures are likely. Normal rainfall, soil moisture and stream flows are likely for 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 25 % 20 % 20 % 20 %
Normal 50 % 50 % 50 % 50 %
Below normal 25 % 30 % 30 % 30 %

West Coast, Alps and Foothills, Inland Otago, Southland:

 

Average temperatures are likely. 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 20 % 30 % 30 % 25 %
Normal 50 % 50 % 50 % 50 %
Below normal 30 % 20 % 20 % 25 %

Coastal Canterbury, East Otago:

 

Average temperatures are likely. 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 % 25 % 20 % 20 %
Normal 50 % 50 % 50 % 50 %
Below normal 20 % 25 % 30 % 30 %

The equatorial Pacific ocean has moved into an El Niño state (with the atmosphere still to adjust), and El Niño conditions are likely to persist through the rest of 2009. Only weak impacts are expected over New Zealand in the coming three month season. 


As the circulation near New Zealand begins to respond to El Niño conditions in the tropical Pacific, we would expect to see a shift to more frequent south-westerlies in the spring. Depending on the intensity of the El Niño, this would suggest a heightened risk of drought in northern and eastern regions over late spring and summer, following a good start to spring (with soil moisture levels likely to be near normal in all regions).

 

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) 3860508 (office DDI)

© Copyright NIWA 2009. All rights reserved. Acknowledgement of NIWA as the source is required.