Climate outlook for July to October
Climate outlook overview
- July to September rainfall is likely to be above median for most of Australia, though areas in western WA, coastal south-east Australia, and western Tasmania are tending towards a more neutral rainfall outlook. July and August rainfall show a similar pattern though the chances of exceeding the median are not as high in August.
- Maximum temperatures for July to September are likely to be above median for the northern tropics and parts of south-west and south-east Australia, while below median daytime temperatures are more likely for a broad area extending from SA across western NSW and into southern Queensland. July and August show a similar pattern, although July is likely to be below median more broadly for much of the southern two-thirds of the mainland.
- Above median minimum temperatures for July to September are likely Australia wide. Likewise, July and August outlooks indicate above median minimum temperatures for most parts of the country.
- Large parts of the eastern Indian Ocean are warmer than average, and a negative Indian Ocean Dipole event is looking increasingly likely, which can favour above average rainfall for parts of Australia. The El Niño–Southern Oscillation is currently neutral.
Above median July to September rainfall for most of Australia
- Rainfall for July to September is likely to be above median for most of Australia (i.e. chance of exceeding median is greater than 60%), with most of the eastern three-quarters away from the coast showing a greater than 80% chance. Parts of western WA, eastern NSW, southern Victoria, and western Tasmania have roughly equal chances of above or below median rainfall (chance of exceeding the median is close to 50%).
- The pattern for July and August is similar to the July to September outlook, though the likelihood of exceeding the median rainfall is not as high in August.
- For the week of 5 to 11 July, rainfall is likely to be above median in a band extending from south-east WA, across SA and into NSW and southern and eastern Queensland. South-west and south-east Australia including Tasmania are likely to have neutral to below median rainfall; this is likely the positive Southern Annular Mode acting against the wetter influence from the Indian Ocean.
- Historical accuracy for July to September rainfall is high to very high for most of Australia, with moderate accuracy for parts of western WA and south-east Australia.
- It should be noted that the northern Australian dry season commenced in May. This means tropical northern Australia (with the exception of the Queensland tropical east coast) typically has very low rainfall totals, and only a small amount of rainfall is needed to exceed the median.
Warmer days for northern tropics and parts of southern Australia, but cooler days for parts of the east; warmer nights nationwide
- Maximum temperatures for July to September are likely to be above median for tropical northern Australia, southern parts of west coastal WA, southern and eastern Victoria, much of eastern NSW, and Tasmania (greater than 60% chance), with most of these areas very likely to have warmer July to September days (greater than 80% chance). Below median daytime temperatures are more likely for a broad area extending from SA across western NSW and into southern Queensland (chance of exceeding the median is 30 to 40% chance). Elsewhere, there are roughly equal chances of above or below median maximum temperatures (chance of exceeding the median is close to 50%).
- July and August maximum temperatures show a similar pattern to July to September, although for July, below median temperatures are likely for much of the southern two-thirds of the mainland away from the south-east.
- Minimum temperatures for July to August are very likely to be warmer than median for most of Australia (chances are greater than 80%); parts of western WA, southern SA and western Victoria have slightly lower chances (60 to 80% chance).
- Likewise, minimum temperatures for July and August are likely to be above median for most areas, although in July southern parts of Australia have roughly equal chances of having warmer and cooler than median overnight temperatures.
- Historical accuracy for July to September maximum temperatures is moderate to high for most parts of Australia, with low accuracy in central Australia. For minimum temperatures, accuracy is moderate to high for most parts of Australia but low to very low in southern and central WA.
Climate influences
- The Bureau's climate model suggests a negative Indian Ocean Dipole (IOD) is likely to develop in winter. An IOD event is declared when the index reflects a positive or negative state for at least 8 weeks. The most recent weekly value of −0.44 °C is the sixth consecutive weekly value below the negative IOD threshold (−0.4 °C). A negative IOD increases the chance of above average winter-spring rainfall for much of southern and eastern Australia.
- More generally, above average sea surface temperatures to the north of Australia and in the eastern Indian Ocean may also be providing more conducive conditions for rainfall across some parts of Australia.
- The El Niño–Southern Oscillation (ENSO) is neutral. Most models indicate neutral ENSO conditions are likely to persist throughout winter and early spring. Tropical central and eastern Pacific sea surface temperatures are forecast to slowly cool over the coming six months, which may be contributing to the wetter than median outlooks for parts of the county.
- The Southern Annular Mode (SAM) index is forecast to remain positive for the next fortnight. This could see cold fronts shifted further south than usual. The positive SAM may be competing against the wet signal across the southern regions in the shorter term, contributing to the neutral to drier outlook across south-west and south-east Australia in the coming fortnight.
- Australia's temperature and rainfall variability are also influenced by global warming caused by human activities. Australia's climate has warmed by around 1.44 °C for the 1910–2019 period, 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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