Southeast Australian temperature outlook

Issued 24 July 2013

Cooler days and nights likely for much of the southeast

Text details of chance of warmer maximum and minimum temperatures

Summary

  • Cooler days and nights are likely over large parts of the southeast mainland, while warmer days and nights are likely across Tasmania
  • Warmer nights are likely across coastal SA and southern Victoria
  • The main climate drivers for this outlook include a 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 over southeast Australia, excluding northern and western parts of SA, with minimum temperature accuracy moderate over Tasmania, western and northeast SA, and northern parts of NSW.
Probability of exceeding median maximum temperature, larger view Probability of exceeding median minimum temperature, larger view

Details

The chances of August to October maximum temperatures exceeding long-term median maximum temperatures are less than 40% over NSW, most of Victoria and Pastoral and eastern districts of SA (see map above). Such odds mean that for every ten years with similar climate patterns to those currently observed, two to four August to October 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 August to October minimum temperatures exceeding long-term median minimum temperatures are less than 40% across eastern NSW, extending into northwest Victoria. Conversely, the chances of warmer than normal nights are in excess of 60% across coastal areas of SA and Victoria while probabilities exceed 80% over Tasmania.

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 in progress, and is expected to persist through 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 is ENSO-neutral. The dynamical seasonal outlook model suggests a brief period of weak La Niña-like conditions forming during the next few months. This has contributed to an increased chance of above normal rainfall for southeast Australia, and hence below average daytime temperatures. 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 being the coolest (most La Niña-like).

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 August to October, historical accuracy shows the outlook for maximum temperatures to be moderately consistent over most of southeast Australia, excluding northern and western districts of SA.

The effect on minimum temperatures during this season is moderately consistent over northeast and western districts of SA, northwest NSW, and Tasmania. Elsewhere, the effect is only weakly to very weakly consistent.