Climate outlook for September to December

Issued 13 August 2020

Climate outlook overview

The fortnight 17 to 30 August is likely to see above average rainfall across most of mainland Australia, although chances are close to average, or favour drier than average conditions, in south-west WA, Tasmania and much of the northern tropics.
The outlook for September to November indicates a wetter than average three-month period for the eastern half of Australia, but drier than average for northern to central WA, and south-west Tasmania.
Days are likely to be warmer than average during spring for Australia's northern tropics, Tasmania, and southern Victoria. Cooler than average days are likely across much of NSW and southern Queensland, but chances of warmer or cooler than average days and nights are roughly equal across much of the southern half of the mainland.
Nights are likely to be warmer than average over most of Australia for September to November, but chances of warmer or cooler than average nights are roughly equal across much of south-west WA.
The tropical Pacific Ocean is expected to approach or exceed La Niña levels by the end of spring, while warmer than average waters are likely in much of the central and eastern Indian Ocean. La Niña and warmer eastern Indian Ocean temperatures typically increase the likelihood of above average rainfall across much of Australia during winter and spring.

The fortnight of 17 to 30 August is likely to be wetter than average for most of Australia (greater than 65% chance across most of the southern half of the mainland), although chances are close to average in south-west WA, Tasmania and much of the northern tropics. The outlook favours a drier than average fortnight (greater than 60% chance) for the far south-west of WA and some areas of the tropics, mostly around the Gulf of Carpentaria.
September to November is likely to be wetter than average across the eastern half of the mainland (greater than 70% chance in most areas), wetter than average in north-eastern Tasmania and drier than average in south-west Tasmania, and also drier than average (greater than 60% chance) over much of northern to central WA.
The northern Australian dry season spans May through September. As tropical northern Australia typically has very low rainfall totals during the dry season only a small amount of rainfall is needed to exceed the median.

Daytime temperatures for the fortnight 17 to 30 August are likely to be warmer than average for most of the northern tropics, but cooler than average for much of the southern half of Australia. Chances of warmer or cooler than average days are close to average in eastern NSW, about the Alps, for most of Tasmania, and south-west WA.
For 17 to 30 August, nights are likely to be warmer for most of Australia, though chances are close to average for most of Tasmania, much of south-west WA, coastal SA, and western and south coast Victoria.
Days during spring are likely to be warmer than average for of Australia's northern tropics and Tasmania (65% to greater than 80% chance) and also for southern Victoria (mostly 60 to 70% chance). The outlook favours cooler than average nights (generally greater than 70% chance) across much of NSW, southern Queensland, and parts of eastern SA and northern Victoria.
Night-time temperatures for spring are very likely to be warmer than average for most of Australia (greater than 80% chance in most areas), although chances are close to equal for much of south-west WA.

The central and eastern tropical Pacific is expected to continue to cool in the coming months. The majority of models anticipate this cooling will exceed La Niña thresholds by the end of spring. A La Niña WATCH is active.
While much of the eastern Indian Ocean remains warmer than average, the Indian Ocean Dipole (IOD) remains neutral. The Bureau's model suggests a neutral IOD is most likely for the coming months.
The Southern Annular Mode (SAM) is currently negative, but is expected to return to weak positive values for the last part of August. A positive SAM during winter can bring drier conditions to the southern reaches of the country including Tasmania, but wetter in northern NSW and southern Queensland.
Australia's temperature and rainfall variability are also influenced by global warming caused by human activities. Australia's climate has warmed by around 1.4 °C since 1910, while southern Australia has seen a reduction of 10–20% in cool season (April–October) rainfall in recent decades.
The Bureau's climate model uses the physics of our atmosphere, oceans, ice and land surface combined with millions of observations from satellites and on land and sea. As a result, it incorporates the influence of climate change and natural climate drivers like ENSO, IOD, the MJO, and SAM in its outlooks.

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