THE CLIMATE KELPIE BLOG: What’s predicted in September?

Posted by BCG on 14th September 2020

In August, the El Niño-Southern Oscillation (ENSO) outlook changed from La Niña ‘Watch’ to ‘Alert’. Driving this shift was the central Pacific Ocean temperatures continuing to cool and the development of stronger than normal trade winds. This means that there is now roughly a 70% chance of a La Niña developing over the coming months which would typically bring ‘Above Average’ rainfall to much of Australia. The Indian Ocean is also looking favourable to help deliver increased rainfall in Spring as temperatures in this ocean are currently ‘Above Average’ and if they continue to warm a negative Indian Ocean Dipole (IOD) could form.

As a result, the overall outlook for Spring is for ‘Above Average’ rainfall for much of Australia except south west Tasmania and the Western Australia coastline where ‘Below Average’ rainfall is likely. For temperature, maximums are likely to be ‘Above Average’ except for parts of southern mainland Australia where they are likely to be ‘Below Average’. Minimums are also likely to be ‘Above Average’ for most of Australia except for the south west of Western Australia where there is an equal chance ‘Above’ or ‘Below Average’ temperatures.

Rainfall Roundup

After a dry start to winter, most of Australia received ‘Above Average’ rainfall in August (Fig. 1). However, there were regions which received ‘Below Average’ rainfall including western Tasmania, and southern parts of Western Australia (Fig. 1).

Despite the rain in August, the overall rainfall totals across much of Australia for the last three months were ‘Below Average’ (Fig. 2). Most notably, Western Australia, with some areas recording the ‘Lowest on Record’. Exceptions to this are the south east of Tasmania, far east of Victoria, south east coast of New South Wales and a few areas in the other states and territories where ‘Above Average’ rainfall was observed over winter (Fig. 2).

Figure 1. Rainfall deciles for August 2020.
Figure 2. Rainfall deciles for June to August 2020.

Rainfall Forecast

The BoM’s ACCESS model predicts that September is likely to deliver equal chances of ‘Above’ or ‘Below Average’ rainfall for much of Australia except for parts of Tasmania, south west Victoria, south east South Australia, the central west to south west coastline of Western Australia and isolated parts of Queensland where ‘Below Average’ rainfall is likely (Fig. 3). For the central third of Australia however, ‘Above Average’ rainfall is likely (Fig. 3).

For the three-month forecast, September to November, rainfall is likely to be ‘Above Average’ for the eastern two thirds of Australia (Fig. 3). However, western Tasmania and along the coastline of Western Australia ‘Below Average’ rainfall is likely (Fig. 3).

At this time of year accuracy for the three-month forecast is moderate to high across Australia except for an area in Western Australia where accuracy is low at this time of year (Fig. 3).

Figure 3. Australian outlook for September to November 2020.

Temperature Roundup

Maximum temperatures in August were ‘Above Average’ across northern Australia with several locations in Western Australia, Northern Territory and Queensland experiencing the ‘Highest on Record’ with some temperatures recorded above 40°C (Fig. 4). In contrast, south eastern Australia was ‘Average’ to ‘Below Average’ for maximum temperatures (Fig. 4).

Minimum temperatures were ‘Above Average’ across much of western and central Australia (Fig. 5). There were only a few small areas across the country which experienced ‘Below Average’ minimum temperatures (Fig. 5)

Figure 4. Maximum temperature deciles for August 2020.
Figure 5. Minimum temperature deciles for August 2020.

Temperature Forecast

The BoM’s ACCESS model forecast suggests that over the next three months maximum temperatures are likely to be ‘Above Average’ across much of Australia except for regions in the eastern states and southern Western Australia where there is roughly equal chances of ‘Above’ or ‘Below Average’ maximum temperatures (Fig. 6).

For minimum temperature, except of the south west of Western Australia where there are equal chances of minimum temperatures being ‘Above’ or ‘Below Average’ during Spring the rest of Australia is likely to be ‘Above Average’ (Fig. 7). Note that frosty nights are also still possible particularly in areas without decent rainfall. 

At this time of year accuracy for the three-month maximum temperature forecast is moderate to high for all of Australia (Fig. 6). For minimum temperature over the next three months accuracy is moderate to high across most of Australia except for a few small pockets in Queensland and the Northern Territory (Fig. 7).

Figure 6. September to November 2020 maximum temperature outlook.
Figure 7. September to November 2020 minimum temperature outlook.

Climate and Water Outlook Videos

The Bureau of Meteorology releases regular outlook videos, covering all this information. Watch the most recent video below.

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