The pattern of seasonal maximum temperature odds across Australia
is a result of the combined effects of above average temperatures
in the Indian Ocean surrounding the west coast of WA, and a
warming trend in the Pacific. The Indian Ocean signal dominates the
Averaged over the September quarter, the chances are between 60 and 75%
for above-normal maximum temperatures over most of WA, the southern
NT, all of SA and Victoria, far southwest Queensland, western NSW
and parts of Tasmania (see map). In a large part of central and
western WA the chances are between 75 and 85%. So for every ten years
with ocean patterns like the current, about six to eight July to September
periods are expected to be warmer than average over these parts of Australia,
with about two to four being cooler.
Over the rest of the country, the chances of exceeding the three-month median maximum
temperature are between 40 and 60%. So the chances of being warmer than normal are
about the same as the chances of being cooler.
Outlook confidence is related to how consistently the Pacific and Indian
Oceans affect Australian temperatures. During the September quarter, history shows this
effect on maximum temperatures to be moderately consistent in WA, the NT,
Queensland, northern and eastern NSW, and far northern Tasmania. Elsewhere
it is only weakly consistent (see background information). Therefore, this outlook
should be used with caution in Victoria, Tasmania, western NSW and much of SA.
The outlook for seasonal minimum temperatures shows a mixed pattern
of odds: warmer nights are favoured in southwest WA (60-70% chances), while
cooler nights are favoured in eastern Queensland (35-40% chances of exceeding
the median) - see map. Over the rest of the country the odds are in
the 40 to 60% range, so the chances of being warmer than average are
similar to the chances of being cooler.
History shows the oceans' effect on minimum temperatures in July to
September to be moderately consistent over Queensland and the east of the NT, the
southern half of WA, and parts of north and east NSW. Elsewhere the
effect is only weakly or very weakly consistent.