Climate outlook for September to December
Climate outlook overview
- The fortnight 31 August to 13 September shows below average rainfall is likely across much of Queensland and parts of southern Australia. Meanwhile, some east-face parts of the coastal northern tropics, south-east WA and western SA, and parts of the south-east mainland coast are more likely to see a wetter than average fortnight.
- The outlook for September to November indicates a wetter than average three-month period for most of Australia, drier than average for south-west Tasmania, and roughly equal chances of wetter or drier conditions across the west and north of WA.
- Days are likely to be warmer than average during September to November for Australia's northern tropics, Tasmania, and the southern half of Victoria. The outlook indicates slightly increased chances of cooler than average days (mostly 55 to 65% chance) 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 south-west WA.
- A La Niña ALERT is active. ENSO indicators in the tropical Pacific Ocean are consistent with La Niña development. La Niña and warmer eastern Indian Ocean temperatures typically increase the likelihood of above average rainfall across much of Australia during spring
A wetter September to November for most of Australia
- The fortnight of 31 August to 13 September is likely to be drier than average for most of Queensland except Cape York Peninsula, and also for parts of the inland north-east of the NT, parts of coastal northern WA, much of Tasmania, south-west WA, southern SA, and western and north-eastern Victoria (greater than 65% chance across most areas).
- There is a chance of a wetter than average fortnight for parts of the east coast of Queensland's Cape York Peninsula, the eastern Top End in the NT, south-east WA and western SA, and parts of the coast in NSW and eastern Victoria.
- September to November is likely to be wetter than average across much of Australia, (greater than 60% chance in most areas, greater than 75% in much of the eastern half of the mainland). Chances of a drier than average spring are seen in south-west Tasmania (greater than 60% chance), and roughly equal chances of wetter or drier conditions across the west and north of WA.
- September is typically the last month of the northern Australian dry season. The Northern Rainfall Onset outlook indicates early rainfall onset is likely for most of northern Australia, but roughly equal chances of an early or late rainfall onset for the western and far northern WA. The northern rainfall onset outlook gives an indication of whether the first significant rains after 1 September are likely to be earlier or later than average.
Warmer nights for most of Australia during September to November; days warmer in the northern tropics but cooler in NSW and adjoining eastern SA
- Daytime temperatures for the fortnight 31 August to 13 September are very likely to be warmer than average for most of Australia (greater than 80% chance in most areas), but favour cooler than average days (mostly 60 to 75% chance) for parts of Queensland’s north tropical and central coast. Chances of warmer or cooler than average days are close to equal for most of the rest of east coast Queensland.
- For 31 August to 13 September, nights are very likely (greater than 80% chance) to be warmer than average for WA and much of the far northern tropics, likely (generally greater than 65% chance) warmer than average for most of the remainder of Australia, while chances of warmer or cooler nights are roughly equal for the inland north-eastern NT.
- Days during September to November are very likely to be warmer than average for most of Australia's northern tropics and Tasmania (mostly greater than 80% chance) and also likely (mostly greater than 65% chance) warmer than average for the southern half of Victoria, extending into the Alpine region and along the coastal fringe of NSW.
- The outlook indicates slightly increased chances of cooler than average days (mostly 55 to 65% chance) across most of the remainder of the southern half of the mainland. The chances of cooler days are highest in coastal south-east WA and around the junctions of the NSW/SA/Victorian borders.
- Night-time temperatures for September to November 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 south-west WA.
- The Bureau's ENSO Outlook is at La Niña ALERT, meaning the chance of La Niña developing in the coming months is around 70%. This is roughly triple the normal risk.
- Indicators in the ocean and atmosphere are generally consistent with La Niña development. Five of eight surveyed international climate models anticipate La Niña thresholds will be reached during September or October.
- Large parts of the Indian Ocean are warmer than average, with some weak cool anomalies near the Horn of Africa. More than half of the surveyed models reach the negative Indian Ocean Dipole (IOD) threshold during early spring 2020.
- The Southern Annular Mode (SAM) is currently negative. However, neutral values are expected for September.
- 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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