Climate outlook for June to September
Climate outlook overview
- Winter (June to August) is likely to be wetter than average across most of Australia.
- However, chances of a wetter than average winter are slightly lower along the NSW and Victorian east coasts, parts of the tropical north, and for most of Tasmania. In these areas, there are roughly equal chances of being wetter or drier than average.
- Winter days are likely to be warmer than average across northern and eastern Australia as well as Tasmania, with much of the southern mainland likely to see cooler days. Winter nights are very likely to be warmer than average nationwide.
- However, cooler days are likely for the fortnight of 25 May to 7 June for much of northern Australia, and closer to normal elsewhere.
- Outlooks suggest a negative Indian Ocean Dipole could develop from mid-winter, while the tropical Pacific Ocean is likely to cool over the winter months.
Wetter winter likely for most of Australia
- Winter (June to August) is likely to be wetter than average (65–80% chance) in southern WA and much of the tropical north, with above average rainfall very likely (chances greater than 80%) for most of the remainder of the mainland. Only the far north of Australia, the NSW and Victorian east coasts, plus Tasmania, have roughly equal chances of a wetter or drier winter.
- Similarly, July to September is also likely to be wetter than average for most of Australia (mostly 65–80% chance, with higher chances for the inland southeast of Australia).
- May marked the official start of the northern Australian dry season. This means tropical northern Australia typically has very low rainfall totals, and only a small amount of rainfall is needed to exceed the median.
Warmer winter days for tropical north and east; cooler for southern mainland
- Cooler days are likely for the fortnight of 25 May to 7 June for much of northern Australia, and closer to normal elsewhere. Much of the northern half of Australia are likely to have days which are 1 to 2 degrees cooler than average, with northern WA 2 to 3 degrees below average. Elsewhere, days are likely to be closer to average.
- Winter (June to August) days are likely to be warmer than average in tropical northern Australia, along the east coast and extending into Tasmania (greater than 80% chance for the tropical north, mostly 60–80% in other parts). However, most of southern and central WA, SA, western NSW and northwestern Victoria are more likely to have cooler winter days (mostly 60–75% chance).
- Winter night-time temperatures are very likely to be warmer than average for most of Australia (65–80% chance for southwest and southeast Australia, greater than 80% chance elsewhere). The southeast coast of SA has roughly equal chances of warmer or cooler than average nights.
Climate influences
- A warmer than average eastern Indian Ocean is increasing the likelihood of northwest cloudbands interacting with rain-bearing fronts and troughs as they sweep across the country.
- While the Indian Ocean Dipole (IOD) is currently neutral, the model outlook suggests a negative IOD will develop from mid-winter. Caution should be exercised when using IOD forecasts issued during autumn, as they are less accurate than forecasts made at other times of the year. However, it should be noted most other international models surveyed by the Bureau also indicate a negative IOD is likely to form during the second half 2020.
- Negative IOD events typically increase the likelihood of above average winter-spring rainfall across southern Australia. They also increase the likelihood of cooler days in the south, and warmer days in the north, a pattern which is largely reflected in the winter maximum temperature outlook.
- The El Niño–Southern Oscillation (ENSO) is likely to remain neutral over winter, though cooling towards La Niña levels is possible by the end of winter.
- The Southern Annular Mode (SAM) is forecast to be positive for the next three weeks. During winter, a positive SAM typically means less rainfall for southwest WA, southern Victoria and Tasmania. This drier influence of SAm appears to be counteracting the wetter influence from the Indian Ocean, with the rainfall outlook in the south for this period largely showing no strong rainfall signal.
- 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 oceans, ice and land surface combined with millions of observations from satellites and on land and sea. As a result, it includes the influence of climate change and natural climate drivers like ENSO, IOD, the MJO and SAM in its outlooks.
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