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

Posted by BCG on 7th July 2020

A weak positive Southern Annular Mode (SAM) was the main driver influencing Australia’s climate over June. In this positive phase, SAM typically brings higher than average air pressure over Australia resulting in ‘Below Average’ rainfall across much of south west Western Australia, southern Victoria and Tasmania. It is however, expected that this SAM pattern will break down by the end of July and in its place the Pacific Ocean and Indian Ocean will begin to influence our climate.

Over the coming months the central and eastern Pacific Ocean is expected to continue cooling resulting in the likely formation of a La Niña which favours ‘Above Average’ winter-spring rainfall across much of eastern, central and northern Australia. There have also been indications that the Indian Ocean may also warm to our north west, resulting in a negative Indian Ocean Dipole (IOD). This could also contribute to ‘Above Average’ winter-spring rainfall to southern and eastern Australia, however, the chances of a -IOD have reduced in recent months.

As a result, the overall outlook for July to September is for ‘Above Average’ rainfall for much of the eastern two-thirds of mainland Australia except for along Victoria’s south west coast, north west Tasmania, the south east coastline of South Australia, the northern tip of Queensland and a large area in northern Western Australia where ‘Below Average’ rainfall is likely. For temperature, both minimums and maximums are likely to be ‘Above Average’ across Australia.

Rainfall Roundup

In June, ‘Below Average’ to ‘Very Much Below Average’ rainfall was recorded across most of Western Australia, Northern Territory, South Australia, western New South Wales and parts of Queensland (Fig. 1). However, pockets in Tasmania, New South Wales and Queensland recorded ‘Above Average’ rainfall (Fig. 1).

For the past three months the south eastern states have recorded ‘Above Average’ rainfall but note that most of this fell in April (Fig. 2). Northern Australia also experienced ‘Above Average’ rainfall however the dry season commenced in May and therefore only a small amount of rainfall is needed for the median to be exceeded. In contrast, large parts of Western Australia and regions within South Australia, North Territory, Queensland and New South Wales recorded ‘Below Average’ to ‘Lowest on Record’ (Fig. 2).

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

Rainfall Forecast

The BoM’s ACCESS model suggests that July is likely to deliver ‘Above Average’ rainfall for parts of northern Australian (Fig. 3). For the rest of Australia however, there are equal chances of rainfall being ‘Above’ or ‘Below Average’ except for the south west and central Western Australia, pockets of the south and north of the Northern Territory, areas in northern and southern Queensland as well as large regions with the south eastern states, where ‘Below Average’ rainfall is likely (Fig. 3).

For the three-month forecast, July to September, rainfall is likely to be ‘Above Average’ through the central regions of Australia and ‘Below Average’ along the south east coast of South Australia, the south west coast of Victoria, north west Tasmania as well as northern Queensland and the top third of Western Australia (Fig. 3). Note that northern Australia is currently in the dry season so low rainfall totals are to be expected. The rest of Australia has equal chances of rainfall being ‘Above’ or ‘Below Average’.

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 and pockets in Western Australia where accuracy is low (Fig. 3).

Figure 3. Australian outlook for July to September 2020.

Temperature Roundup

Maximum temperatures in June were ‘Above Average’ across much of Australia with Darwin recording its warmest June day on record (35°C) (Fig. 4). Minimum temperatures were also ‘Above Average’ across much of Western Australia, Northern Territory, Queensland, Tasmania and along the New South Wales coastline. However, ‘Below Average’ minimum temperatures were recorded throughout central and south east Australia as well as small areas in Western Australia (Fig. 5).

Figure 4. Maximum temperature deciles for June 2020.
Figure 5. Minimum temperature deciles for June 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). At this time of year, accuracy for the three-month maximum temperature forecast is moderate to high for most of Australia, except for an area on the border of Queensland and the Northern Territory where accuracy is low (Fig. 6). For the minimum temperature’s, accuracy is moderate to high across most of Australia except for a large area of Western Australia where accuracy is low (Fig. 7).

Figure 6. July to September 2020 maximum temperature outlook.
Figure 7. July to September 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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