Western Australian temperature outlook

Issued 24 July 2013

Warmer days and nights likely for northern and western WA

Text details of chance of warmer maximum and minimum temperatures

Summary

  • Warmer than normal days are likely over the Kimberley and western WA
  • Warmer than normal nights likely over the Kimberley, western and southern WA
  • 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
  • Outlook accuracy for maximum temperatures is moderate over western and southern WA, and parts of the far north, with minimum temperature accuracy moderate over the Kimberley.
Probability of exceeding median maximum temperature, larger view Probability of exceeding median minimum temperature, larger view

Details

The chances of the August to October maximum temperature exceeding the long-term median maximum temperature are greater than 60% over much of the Kimberley and western WA, and over 80% in western parts of the Southwest Land Division (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 40% chance of warmer than normal days over far eastern central parts of WA. In other words, there is a 60% chance of cooler than normal days over this area.

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 Kimberley, and western and southern WA. Probabilities exceed 80% over the Southwest Land Division and much of the Kimberley.

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 typically increases the chances of above normal rainfall, and thus cloud amount, over southern Australia, with increased cloudiness reducing sunshine hours, and hence daytime temperatures. However, the outlook suggests this is most likely to impact the far eastern central parts of WA.

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 WA. 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 the August to October period, historical accuracy shows the outlook for maximum temperatures to be moderately consistent over western and southern WA, and parts of the far north.

The effect on minimum temperatures during this season is moderately consistent over the Kimberley. Across the remainder of WA, the effect is only weakly to very weakly consistent.