Western Australian 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 north Kimberley, and near the western and southern coasts of WA (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 35 to 40% chance of warmer than normal days over an area near the WA-NT-SA border. In other words, there is a 60 to 70% chance of cooler than normal days over this area.
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 Kimberley, northwest, western, and southern WA. Probabilities exceed 80% over much of the Southwest Land Division of WA. For inland central parts of the State, there is no strong tendency towards being warmer or cooler than average.
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 the July to September period, historical accuracy shows the outlook for maximum temperatures to be moderately to highly consistent over most of WA.
The effect on minimum temperatures during this season is moderately consistent over eastern WA, and an area in the west Pilbara. In the remainder of western WA, the effect is only weakly to very weakly consistent.