Southeast Australian temperature outlook

Issued 19 June 2013

Cooler days, warmer nights likely for much of the southeast

Text details of chance of warmer maximum and minimum temperatures

Summary

  • Cooler days are more likely over most of the southeast mainland, while warmer days are more likely across Tasmania
  • Warmer nights are more likely over most of Victoria, southeast NSW and Tasmania
  • Climate influences include a developing negative Indian Ocean Dipole, a neutral-to-cool tropical Pacific, and warm sea surface temperatures around most of Australia
  • Outlook accuracy for maximum temperatures is moderate to high over southeast Australia, with minimum temperature accuracy moderate over Tasmania, southwest SA, and eastern parts of NSW and Victoria.
Probability of exceeding median maximum temperature, larger view Probability of exceeding median minimum temperature, larger view

Details

The chances of July to September maximum temperatures exceeding long-term median maximum temperatures are less than 40% over most of NSW, northern and central Victoria and eastern SA (see map above). Such odds mean that for every ten years with similar climate patterns to those currently observed, two to four July to September periods would be expected to be warmer than average over these areas, while about six to eight years would be cooler.

Conversely, the chances of warmer than normal days exceed 80% over Tasmania.

The chances of July to September minimum temperatures exceeding long-term median minimum temperatures is in excess of 60% over southwest SA, southeast NSW and most of Victoria. Probabilities exceed 80% over Tasmania and a small area of eastern Victoria.

Over the rest of southeast Australia, there is no strong tendency towards warmer or cooler nights than average.

Climate influences

A negative Indian Ocean Dipole (IOD) event is favoured to develop during winter-spring 2013. A negative IOD during winter-spring increases the chances of above normal rainfall, and thus cloud amount, over southeast Australia. Increased cloudiness reduces sunshine hours, and hence daytime temperatures, over inland Australia.

The tropical Pacific has remained ENSO-neutral since mid-2012. The dynamical seasonal outlook model indicates an increased likelihood of La Niña forming during the next few months. However, international climate models surveyed by the Bureau of Meteorology suggest ENSO-neutral is the most likely outcome over the coming season, with the Bureau model showing stronger odds than most of a weak La Niña.

Warmer than normal sea surface temperatures currently surround much of southern Australia. Warmer sea surface temperatures will tend to influence air temperatures in those areas closer to the coast.

How accurate is the outlook?

Outlook accuracy is related to how consistently the oceans and broadscale climate affect Australian temperatures. During July to September, historical accuracy shows the outlook for maximum temperatures to be moderately to highly consistent over southeast Australia.

The effect on minimum temperatures during this season is moderately consistent over Tasmania, eastern NSW, southeast Victoria and southwest SA. Elsewhere, the effect is only weakly to very weakly consistent.