The pattern of seasonal temperature odds across southeastern Australia is
largely a result of a warming trend in the Indian Ocean. Although there has
been some warming in recent months in the equatorial Pacific, it is generally in a
neutral state, and not contributing to any significant shifts in the odds for the
temperature outlook in southeastern Australia.
Averaged over September to November, the chances of above average maximum temperatures
are mainly between 55 and 60% over southeastern Australia, increasing to 60 to 65% in the
southeast of SA, as well as in western and central Victoria (see map). So for every ten years
with ocean patterns like the current, average spring daytime temperatures are higher
than normal in about six, especially in western Victoria and southeast SA, while
about four out of ten are cooler.
Outlook confidence is related to how consistently the Pacific and Indian
Oceans affect Australian temperatures. During spring, history shows this effect on
maximum temperatures to be moderately consistent across most of NSW and South
Australia. However, over far southern NSW, Victoria, and most of Tasmania confidence is
only weakly consistent so this outlook should be used with caution in those areas (see background information).
There is a moderate to strong shift in the odds towards warmer average spring minimum temperatures,
with nights favoured to be warmer than normal across southeastern Australia, except
for the northeast half of NSW where the outlook is neutral (see map). The chances of
increased overnight warmth (averaged over the coming three months) are between
60 and 80% in SA, Victoria and the southwest half of NSW. This means for every ten
years with ocean patterns like the current, about six to eight would be expected to
be warmer than average in terms of overnight temperatures averaged over spring. In Tasmania the
probabilities are lower at between 60 to 70%.
History shows the oceans' effect on minimum temperatures during spring to be
moderately consistent over SA and western parts of NSW. However, over
much of eastern and southern NSW, Victoria and Tasmania, the effect is generally
only weakly consistent, so this outlook needs to be used with caution in these areas.