August Outlook for Australia

Despite cooling of sea-surface temperatures anomalies across the equatorial central and eastern Pacific in recent months and warmer-than-normal waters off western and northern Australia rainfall has been running below normal across much of southern Australia since 1 June.

A couple of factors likely leading to the drier conditions across much of southern Australia so far this austral winter has to be the slow-moving Madden-Julian Oscillation (MJO) that has been largely in phases 1 and 2 since 31 May. Looking at the image below, we can see that phases 1, 2 and 3 of the MJO are not conducive to wet weather in southern Australia. The more favorable phases of the MJO for rainfall in Australia are phases 4, 5 and 6.

Another factor is the Antarctic Oscillation (AAO) or Southern Annular Mode (SAM). The AAO/SAM was predominately positive during June before turning negative at times in July. A negative AAO/SAM tends to favor more rain in southern Australia during winter, and there have been more frequent fronts over the region at times in July, but overall rainfall amounts have been insufficient to get rainfall to normal in many areas.

Looking forward, the AAO/SAM is expected to be predominately weakly positive during August which should result in good rains across eastern and northern New South Wales into southern Queensland. A +AAO should mean dryness concerns across southwestern and far southeastern Australia. Meanwhile, the MJO will likely be weak early in August and shows no signs of entering more favorable phases at least through mid-August. Overall, we expect the MJO to be a minor factor during August, especially early in the month.

Another factor to watch is the continued cooling of the waters across the equatorial central and eastern Pacific as weak La Nina conditions are expected to develop for austral spring. La Nina conditions are typically favorable for rainfall in eastern Australia, so continued cooling of water temperatures could become beneficial for rains in eastern Australia later in August.

Looking at some climate model outputs from the APEC Climate Center multi-model ensemble as well as the NMME most modeling seems to favor wetter-than-normal conditions across parts of eastern Australia.

Based on teleconnections and model output we are favoring above-normal rainfall across much of New South Wales, southern Queensland and northern South Australia during August. However, there is a risk that far southern and western New South Wales and much of South Australia can have normal or even below-normal rainfall.

We are expecting rainfall to be below normal over southeastern South Australia, Victoria and southwestern Western Australia. However, any drops of the AAO into negative territory can lead to brief spells of wet weather over southern Australia as we saw in July. There is a small chance that southwestern Australia can have normal rainfall thanks to any -AAO periods. Much of the rest of Australia will have close to normal rainfall.

Temperatures across Australia during August are expected to average near normal across the south with mostly above-normal temperatures expected farther north. However, portions of southern Australia can be biased a bit warmer than normal, while coastal New South Wales and the southeastern coast of Queensland has the risk of having temperatures averaging near normal.

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