Climate outlook for September to December

Climate outlook overview

• September to November rainfall is likely to be above median for the eastern two thirds of Australia, but below median for south-western Tasmania and south-west Western Australia.
• September rainfall is likely to be above median for much of Australia, with the chance of above median rainfall more widespread in September than later in the season.
• September to November maximum temperatures are likely to be above median for the tropics, south-west Western Australia, and Tasmania; cooler than median days are likely across much of the mainland south of the tropics excluding the west of Western Australia and much of Victoria.
• Minimum temperatures generally likely to be warmer than median for September to November over much of Australia, although there is roughly equal likelihood of warmer or cooler nights along the New South Wales central coast northwards to south-eastern Queensland, and through much of central to southern Western Australia and western South Australia.
• The negative Indian Ocean Dipole event, increasing chance of La Niña emerging during spring, positive Southern Annular Mode index, and warmer than average waters around northern Australia are likely to be influencing this outlook.

Wetter than average September to November likely for eastern two thirds of mainland Australia

• There is a moderate to high chance (greater than 75%) of above median rainfall for the fortnight 5 to 18 September for much of the eastern two thirds of mainland Australia, and eastern Tasmania; there is a moderate chance (greater than 60%) of below median rainfall for much of western Tasmania.
• During that fortnight, much of north and east of the Northern Territory, Queensland, most of New South Wales and Victoria except areas eastward of the Great Dividing Range, and large parts of southern South Australia have at least 2.5 times the average chance of unusually high rainfall (in the wettest 20% of all 5 to 18 September periods during 1981 to 2018).
• September is the wettest month of the outlook period, with rainfall likely to be above median for most of Australia except for western Tasmania, eastern Victoria, and along the west and north coast of Western Australia; the increased likelihood of above median rainfall becomes more focused towards the east of Australia as the season progresses.
• There is a moderate to high chance (greater than 70%) of above median September to November rainfall for much of the eastern two thirds of mainland Australia and eastern Tasmania, above median rainfall very likely (greater than 80% chance) for northern Victoria, most of New South Wales and Queensland, and the Top End in the Northern Territory; below median rainfall is likely for south-west Tasmania and south-west Western Australia.
• Large parts of the Top End and far northern Queensland have more than three times the average chance of unusually high September to November rainfall (in the wettest 20% of all such periods over 1981–2018), with unusually high rainfall for the season at least two times more likely than average over much of the eastern mainland states, eastern Tasmania, and most of the north and east of the Northern Territory.
• Past accuracy for September to November chance of above median rainfall outlooks is moderate to very high for most of Australia with the exceptions of parts of Western Australia, most notably in the north-west and in an area inland around the border with South Australia, where it is generally moderate to low.

Warmer days likely for the tropics and Tasmania during September to November, but cooler for much of the rest of the mainland

• For the fortnight 5 to 18 September, maximum temperatures are likely to be above median for most of the northern tropics (greater than 70% chance), but below median (greater than 70% chance) for most of the remainder of the mainland and for eastern Tasmania.
• For the fortnight 5 to 18 September, minimum temperatures are likely to be above median for much of the northern tropics (greater than 70% chance), but there is a moderate likelihood (greater than 75% change) of below median minimum temperatures for much of the interior of Western Australia, and along the east coast of Australia from far south-east Queensland to the Illawarra in New South Wales.
• For that fortnight, there is more than double the average chance of unusually high maximum and minimum temperatures (in the warmest 20% of all 5 to 18 September periods during 1981 to 2018) across the far northern tropics; however, there is two to three times the average chance of unusually cool maximum temperatures (in the coolest 20%) across large parts of the remainder of the mainland, and more than three times the usual chance in a band from the inland Gascoyne in Western Australia through to northern and central New South Wales inland of the ranges and across the southern half of Queensland.
• Maximum temperatures for September to November are likely (greater than 65% chance) to be above median across the northern tropics, south-west Western Australia, and Tasmania; below median maximum temperatures are likely across much of the mainland south of the tropics excluding the west of Western Australia and much of Victoria and far south-east South Australia.
• Minimum temperatures are generally likely to be warmer than median for September to November over much of Australia, although there is roughly equal likelihood of warmer or cooler nights through much of central to southern Western Australia and western South Australia, and along the New South Wales central coast northwards to south-eastern Queensland; there is a greater than 70% chance minimum temperatures will be cooler than median for parts of coastal north-east New South Wales and south-east Queensland.
• For September to November, there is more than double the average chance of unusually high maximum temperatures (in the warmest 20% of all September to November periods over 1981–2018) across large parts of the far northern tropics, and most of Tasmania away from the east coast.
• Unusually cool maximum temperatures (in the coolest 20% of all September to November periods over 1981–2018) are at least two times more likely than average across much of New South Wales, the southern half of Queensland, and most of South Australia except the south-east.
• There is at least double the average chance of unusually high minimum temperatures (in the warmest 20% of all September to November periods over 1981–2018) for much of northern Australia, Tasmania, and Victoria, rising to four times the average chance for much of the northern tropics.
• Past accuracy for September to November chance of above median maximum temperature outlooks is high to very high across all of Australia. For minimum temperatures, accuracy is high to very high for most of Australia.

Climate influences

The climate outlook reflects several significant climate influences. These include:

• At least a 70% chance of La Niña reforming later in 2022, with the ENSO Outlook currently at La Niña ALERT. Four of the seven models are suggesting La Niña thresholds are likely to be met by early to mid-spring.
• A negative Indian Ocean Dipole (IOD) event, which is currently under way. Outlooks indicate the negative IOD is likely to persist until at least the end of spring. A persistent negative IOD phase increases the chance of above average spring rainfall for much of Australia. It also increases the chances of warmer days and nights for northern Australia.
• The Southern Annular Mode (SAM) index, which is currently strongly positive, and is expected to remain mostly positive throughout spring. Positive SAM has a drying influence for parts of south-west and south-east Australia at this time of year, but increases the likelihood of rainfall in eastern New South Wales, far eastern Victoria, and parts of southern Queensland.
• Sea surface temperatures, which are currently warmer than average over the Maritime Continent and around much of Australia. This pattern is likely to be contributing to the wetter outlooks.
• Australia's temperature and rainfall variability are also influenced by global warming caused anthropogenic influences (human activities). Australia's climate has warmed by around 1.47 °C in the period between 1910 and 2020, leading to increased frequency of extreme heat events, reduction in cool season (April–October) rainfall in southern Australia (10 to 20%) in recent decades, and increased proportion of rainfall from high intensity, short duration rainfall events, particularly across northern Australia.

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.