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

Posted by BCG on 10th August 2020

Like last month, a weak positive Southern Annular Mode (SAM) is currently the main driver influencing Australia’s climate. In this positive phase, SAM is continuing to bring higher than average air pressure over Australia, which is helping to keep things dry for now, but it is expected to break down very soon. As has been forecast for several months now the Pacific Ocean is still expected to approach La Niña thresholds over the coming months and ‘Above Average’ temperatures are likely in much of the central and eastern Indian Ocean which is also likely to bring wetter conditions to Australia.

As a result, the overall outlook for August to October is for ‘Above Average’ rainfall for most of the eastern two-thirds of mainland Australia but ‘Below Average’ rainfall for the north west of Western Australia. For temperatures, both maximum and minimums are likely to be ‘Above Average’ for most of Australia except for south west Western Australia where there is an equal chance of ‘Above’ or ‘Below Average’ maximum and minimum temperatures occurring.

Rainfall Roundup

In July, much of Australia received ‘Below Average’ to ‘Very Much Below Average’ rainfall. However, some regions across the country did experience ‘Above Average’ rainfall, most notably the east coast of New South Wales where two Tasman lows brought heavy rainfall resulting in July totals being ‘Very Much Above Average’. For example, Moruya, on the south east coast of New South Wales received 351mm across three days (Fig. 1).

For the past three months, much of southern Australia has recorded ‘Below Average’ rainfall with some regions recording the ‘Lowest on Record’ (Fig. 2). In contrast, areas along the east coast of New South Wales and Victoria have experienced ‘Above Average’ rainfall over the last three months (Fig. 2). Northern Australia has also experienced ‘Above Average’ rainfall however it’s important to remember that the dry season commenced in May and therefore only a small amount of rainfall is needed for the median to be exceeded.

Figure 1. Rainfall deciles for July 2020.
Figure 2. Rainfall deciles for May to July 2020.

Rainfall Forecast

The BoM’s ACCESS model predicts that August is likely to deliver ‘Above Average’ rainfall through much of Western Australia, South Australia, New South Wales, as well as pockets in Queensland and the Northern Territory (Fig. 3). For the rest of Australia however, there are equal chances of rainfall being ‘Above’ or ‘Below Average’ except for the south-west of Western Australia, northern Queensland, north west Tasmania and along the Limestone Coast in South Australia (Fig. 3).

For the three-month forecast, August to October, rainfall is likely to be ‘Above Average’ through much of the eastern two thirds of Australia (Fig. 3). For Western Australia however, most of the state has equal chances of rainfall being ‘Above ‘ or ‘Below’ average with some regions in the north and a small area in the far south west likely to experience ‘Below Average’ rainfall over the next three months.

At this time of year accuracy for the three-month forecast is moderate to high across Australia except for Gippsland in Victoria, the far south east corner of New South Wales, a small area in northern Queensland and pockets in Western Australia where accuracy is low (Fig. 3).

Figure 3. Australian outlook for August to October 2020.

Temperature Roundup

Maximum temperatures in July were ‘Above Average’ across much of Australia with parts of Western Australia experiencing days that were the warmest on record (Fig. 4). Minimum temperatures were also ‘Above Average’ across parts of Western Australia, Northern Territory, Queensland and along Australia’s eastern coastline. However, ‘Below Average’ minimum temperatures were recorded through central parts of Australia (Fig. 5)

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

Temperature Forecast

The BoM’s ACCESS model forecast suggests that over the next three months both maximum and minimum temperatures are likely to be ‘Above Average’ for most of Australia (Fig. 6 & 7). The south-west of Western Australia however has equal chances of both minimum and maximum temperatures being ‘Above’ or ‘Below’ average (Fig. 6 & 7). At this time of year accuracy for the three-month maximum temperature forecast is moderate to high for most of Australia except for a small pocket in the Northern Territory where accuracy is low (Fig. 6). For the minimum temperature’s accuracy is again moderate to high across most of Australia except for the south west of Western Australia and along the eastern coastline of the Eyre Peninsula in South Australia where accuracy is low (Fig. 7).

Figure 6. August to October 2020 maximum temperature outlook.
Figure 7. August to October 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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