National temperature outlook
Issued 19 June 2013
The chances of the July to September maximum temperature exceeding the long-term median maximum temperature are greater than 60% over the tropical north, the western WA coastline, 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 July to September 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 southern and central Queensland, most of NSW, northern and central Victoria, eastern SA, and an area near the WA-NT-SA border. 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 July to September will exceed the long-term median minimum temperature is in excess of 60% over the tropical north and southern Australia, extending up through western WA. Probabilities exceed 80% over the southwest of WA, much of the northern Australian coastline, and Tasmania.
Over the rest of the country, the chance of receiving warmer or cooler night-time temperatures is roughly equal (i.e., close to 50%).
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 southern 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. This has increased the 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 showing stronger odds than most of a weak La Niña.
Warmer than normal sea surface temperatures currently surround much of western and 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 Australia.
The effect on minimum temperatures during this season is moderately consistent over eastern WA, most of the NT, eastern and central Queensland, eastern NSW and Tasmania. Elsewhere, the effect is only weakly to very weakly consistent.