Western Australian temperature outlook
Issued 28 August 2013
The chances of the spring maximum temperatures exceeding the long-term median maximum temperature are greater than 60 % in large parts of northern and western WA, and over 80% in the southwest corner (see map above). Such odds mean that for every ten years with similar climate patterns to those currently observed, about six to eight spring periods would be expected to be warmer than average over these areas, while about two to four years would be cooler.
The chances that the average minimum temperature for spring will exceed the long-term median minimum temperature are greater than 60 % for most of WA. Probabilities exceed 80% in the far north Kimberley and southwest corner. In southeast WA, the chances of warmer or cooler night-time temperatures are roughly equal.
The negative Indian Ocean Dipole (IOD) event that has been influencing Australian climate since mid-May has weakened over the past four weeks. Despite this, sea surface temperature patterns continue to be consistent with a negative dipole event. The majority of climate models expect this negative IOD event to persist until mid-spring. 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 eastern and southern parts of WA.
The tropical Pacific has remained ENSO-neutral since mid-2012. The dynamical seasonal outlook model suggests ENSO-neutral conditions will remain for the rest of 2013. This means there is no strong shift in the odds from the tropical Pacific, and is reflected to some degree in the temperature outlook, with much of the southern half of the country having odds close to 50% for maximum temperatures.
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 September to November period, historical accuracy shows the outlook for maximum temperatures to be moderately consistent over the eastern half of WA and southwest coast.
The effect on minimum temperatures during this season is moderately consistent over southeast WA. Across the remainder of WA, the effect is only weakly to very weakly consistent.