Climate outlook for June to September

Climate outlook overview

  • Winter (June to August) is likely to be wetter than average for most of Australia.
  • However, chances of a wetter than average winter are slightly lower along the NSW and Victorian east coasts, while parts of the tropical north and southern Tasmania 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 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.
  • 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. 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 Australia

  • The winter months of June to August are likely to be wetter than average for virtually all of Australia (mostly 65–80% chance in WA, much of the tropical north and areas east of the Great Dividing Range, with chances greater than 80% generally elsewhere). However, the likelihood of a wetter or drier winter is roughly equal across the far north of Australia 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). 
  • 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 north and east; cooler for southern mainland

  • 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, most of southern and central WA, SA, western NSW and western Victoria 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 (65–80% 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 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, 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 towards La Niña levels is possible by the end of winter. 
  • The Southern Annular Mode (SAM) is forecacst to be neutral for the next three weeks. During winter, a positive SAM typically means less rainfall for southwest WA, southern Victoria and Tasmania, while a negative SAM means more rainfall for these regions. A neutral SAM has little influence on Australian climate. 
  • 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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