Climate outlook for June to September
Climate outlook overview
- The week of 11 to 17 May is likely to be drier than average for most of the eastern two-thirds of Australia, but wetter for parts of central and western WA.
- Winter (June to August) is likely to be wetter than average for most of the continent. However, parts of the tropical north—which are now into their dry season—have roughly equal chances of being wetter or drier than average.
- Winter days are likely to be warmer than average across northern and eastern Australia with areas in the southeast to the west of the Divide likely to see cooler days. Winter nights are very likely to be warmer than average nationwide.
- A warmer than average eastern Indian Ocean is currently the main influence on Australia's climate, increasing the moisture available to weather systems as they sweep across the country.
Wetter winter likely for most of Australia
- The week of 11 to 17 May is likely to be drier than average for much of northern, eastern and southern Australia (mostly 60–80% chance), with a wetter week likely for the Pilbara, Gascoyne and interior WA (mostly 60–70% chance, increasing to greater than 80% chance for the Pilbara).
- However, the winter months of June to August are likely to be wetter than average for most of Australia (mostly 65–80% chance, with higher chances across southeast and central Australia). The likelihood of a wetter or drier winter is roughly equal across the tropical north, and southern Tasmania.
- 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 eastern two-thirds of Australia).
- It should be noted that May marks 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 north and east; cooler for inland southeast
- For the week of 11 to 17 May, cooler than average days are likely for most of Australia, although warmer than average days are likely for the far north. Nights are likely to be cooler than average for southern, central and eastern Australia, with warmer nights more likely for the far north of Australia and northern and central WA.
- Winter (June to August) days are likely to be warmer than average in 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, southeast SA, northwest Victoria and southwest NSW are more likely to have cooler winter days (60–70% chance).
- Winter night-time temperatures are very likely to be warmer than average for most of Australia (70–80% chance for southwest and southeast Australia, greater than 80% chance elsewhere).
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 during late autumn and into early winter.
- While the Indian Ocean Dipole (IOD) is currently neutral, the outlook suggests a negative IOD could 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 all other international models surveyed by the Bureau also indicate a negative IOD is likely to form during 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 most likely to remain neutral over winter, though cooling of the tropical Pacific Ocean is likely, with some chance that ocean temperatures could reach La Niña levels late in winter or early spring.
- In the shorter-term, higher pressure systems are expected to dominate much of Australia in early May, corresponding with the expected drier week of 11 to 17 May.
- The Southern Annular Mode (SAM) has recently been negative, but is forecast to briefly rise into positive values before becoming neutral for the next three weeks. During autumn, SAM has little influence on Australian rainfall, though winter marks the time of the year when a positive SAM can mean more rainfall over parts of eastern Australia, but less rainfall in southwest WA, southern Victoria and Tasmania.
- 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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