National temperature outlook
Issued 28 August 2013
The chances of the spring 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 spring 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 30 to 40% chance of warmer than normal days over southern NSW, northern and central Victoria and far southeastern parts of SA. In other words, there is a 60 to 70% chance of cooler than normal days over these areas.
The chance that the average minimum temperature for spring will exceed the long-term median minimum temperature is in excess of 60% over the northern half of the continent, extending through western WA, central SA and Tasmania. Probabilities exceed 80% over the tropical northern coasts, the far southwest and Tasmania.
Over the rest of the country, 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 the winter-spring period 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, while over parts of northern Australia it increases the chance of higher humidity.
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 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 spring, historical accuracy shows the outlook for maximum temperatures to be moderately to highly consistent over most Australia, excluding parts of WA (see further details below).
The effect on minimum temperatures during this season is moderately to highly consistent over eastern WA, most of the NT, SA, southern Queensland, most of NSW, Victoria and Tasmania. Elsewhere, the effect is only weakly to very weakly consistent.