National temperature outlook

Issued 24 July 2013

Cooler days likely for most of eastern Australia; warmer days for north and west coasts

Text details of chance of warmer maximum and minimum temperatures

Summary

  • Cooler than normal days are likely over most of eastern mainland Australia, while warmer than normal days are likely over the tropical north, western WA, and Tasmania
  • Warmer than normal nights likely over the tropical north, western WA and the southern coastline and Tasmania
  • Cooler than normal nights are likely over southeast Queensland, most of NSW, and northwest Victoria
  • The main climate drivers for this outlook include a negative Indian Ocean Dipole, a neutral-to-cool tropical Pacific, and warmer than normal sea surface temperatures around the coast of Australia
  • Outlook accuracy for maximum temperatures is moderate over eastern Australia, western WA, and parts of the north, with minimum temperature accuracy moderate over northern Australia and Tasmania.
Probability of exceeding median maximum temperature, large image Probability of exceeding median minimum temperature, large image

Details

The chances of the August to October maximum temperature exceeding the long-term median maximum temperature are greater than 60% over the tropical north, western WA, and Tasmania (see map above). Such odds mean that for every ten years with similar climate patterns to those currently observed, about six to eight August to October periods would be expected to be warmer than average over these areas, while about two to four years would be cooler.

Conversely, there is a 20 to 40% chance of warmer than normal days over the southern NT, the southern half of Queensland, northern and eastern SA, NSW, and Victoria. In other words, there is a 60 to 80% chance of cooler than normal days over these areas.

The chance that the average minimum temperature for August to October will exceed the long-term median minimum temperature is in excess of 60% over the tropical north, western WA, the mainland southern coastline, and Tasmania. Probabilities exceed 80% over the southern and western WA, much of the northern Australian coastline, and Tasmania.

There is a 25 to 40% chance of warmer than normal nights over southeast Queensland, most of NSW, and northwest Victoria. In order words, there is a 60 to 75% chance of cooler than normal nights over these areas.

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 southern 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 northern and eastern Australia. 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 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 eastern Australia, the tropical north, and the southwest half of WA. Elsewhere, the accuracy is only weakly to very weakly consistent.

The effect on minimum temperatures during this season is moderately consistent over the northern half of Australia, most of SA, and Tasmania. Elsewhere, the effect is only weakly to very weakly consistent.