Climate outlook for September to December
Climate outlook overview
- The fortnight 7 to 20 September shows below average rainfall is likely across much of Australia, though wetter than average conditions are expected for the Kimberley, northern interior of WA, and pastoral SA.
- The spring outlook indicates a wetter than average three months for the eastern two thirds of Australia but drier than average for west coast Tasmania, and large parts of west and north-west WA.
- Spring days are likely to be warmer than average for most of Australia. Chances of warmer or cooler than average days are roughly equal for the west and south coasts of WA.
- Spring nights are likely to be warmer than average over most of Australia. 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.
- The Indian Ocean Dipole (IOD) index has been at negative values for the past three weeks; most models anticipate this will continue long enough to be considered a negative IOD event.
- La Niña and a negative IOD typically increase the likelihood of above average rainfall across much of Australia during spring.
A wetter spring for much of Australia, drier in the west
- The fortnight of 7 to 20 September is likely to be drier than average for much of the eastern states, south-east SA, large parts of the central north and east of the NT, and the west of WA (greater than 65% chance across much of Victoria and northern Tasmania, greater than 75% chance for west coast WA).
- There is a chance of a wetter than average fortnight for areas of the northern and Kimberley in WA, extending into the northern interior of WA and large parts of pastoral SA. Chances of a wetter than average fortnight exceed 75% in the northern coastal Kimberley, and are generally less pronounced elsewhere.
- September to November is likely to be wetter than average across the eastern two thirds of mainland Australia and in north-east Tasmania (greater than 75% chance in much of the eastern half of the mainland). Chances of a drier than average spring are seen in western Tasmania and much of west coast and north-west WA (greater than 60% chance in WA, up to greater than 80% chance in parts of west coast Tasmania).
- The September map indicates much of the drier spring signal may originate in this month. September is likely to be drier than average for the west coast of WA (greater than 70% chance in some areas), and also for parts of western and northern Tasmania and for far south-eastern SA and south-western Victoria. The month is likely to be wetter than average for much of eastern WA, the NT, and pastoral areas of SA (greater than 70% chance in the northern Kimberley and adjacent NT).
Warmer days and nights for most of Australia during spring
- Daytime temperatures for the fortnight 7 to 20 September are very likely to be warmer than average for most of Australia (greater than 80% chance in most areas). Chances of warmer or cooler than average days are close to equal for much of Queensland’s north tropical and central coast.
- For 7 to 20 September, nights are very likely (greater than 80% chance) to be warmer than average for much of Australia. However, chances are weaker (generally greater than 60% chance) for much of south-west and southern WA, inland north-eastern NT, south-east SA and south-west Victoria, extending into parts of north-west and central Victoria.
- Days are likely to be warmer than average during September to November for most of Australia. Chances are mostly greater than 80% for Australia's northern tropics, inland of the ranges in eastern Victoria, and across Tasmania. The outlook indicates chances of warmer days are generally weaker over much of central SA, north-west Victoria, north-east NSW, and south-east Queensland (mostly 55 to 65% chance), while chances of warmer or cooler than average days are roughly equal for the west coast and south coast of WA.
- 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 in the west of the basin. Values of the Indian Ocean Dipole (IOD) index have been at negative IOD levels for three consecutive weeks.
- For this to be considered an official negative IOD event the IOD index needs to remain at or cooler than −0.4 °C for eight weeks. Four of the six surveyed models anticipate negative IOD values through October and November.
- The Southern Annular Mode (SAM) is currently negative. However, neutral values are expected for the rest of 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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