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

Posted by BCG on 6th September 2021

The Indian Ocean Dipole (IOD) has remained around the negative threshold level and is forecast to remain in this state for the rest of Spring before returning to neutral in December. A negative IOD greatly increases the chances of ‘Above Average’ rainfall across southern and eastern Australia during winter and spring. Large parts of the eastern Tropical Pacific Ocean also remain warmer than average which can have a favourable impact on spring rainfall for parts of Australia.

In terms of the El Niño–Southern Oscillation (ENSO), this climate driver remains neutral and is predicted to stay this way for the rest of the year. However, it is still anticipated that ocean temperatures in the tropical Pacific Ocean will continue to cool and whilst this might not be enough for a La Niña to form this cooling may also increase the chances of ‘Above Average’ spring rainfall for much of eastern and northern Australia.

Our shorter-term climate driver, the Southern Annular Mode (SAM) is currently positive and forecast to remain this way for the next fortnight. A positive SAM typically has a drying influence on south-west and south-east parts of Australia, but can have a wetter influence on SE Coastal areas at this time of year.

The Madden-Julian Oscillation (MJO) is currently over the western Indian Ocean and predicted to be slow moving in this region. Whilst its not having a direct influence on Australia’s rainfall patterns it is helping to increase cloudiness over the eastern Indian Ocean and south east Asia.

The overall outlook for September to November is for the likely rainfall to be ‘Above Average’ for the eastern two-thirds of Australia, extending into south east Western Australia but ‘Below Average’ for parts of Western Australia and south west Tasmania. In terms of temperatures, minimums are likely to be ‘Above Average’ much of Australia except for south west Western Australia where ‘Below Average’ minimums are likely. Maximum temperatures are forecast to be ‘Above Average’ for northern Australia, southern parts of Victoria and Tasmania with ‘Below Average’ maximums likely for southern and central regions of Australia.

Rainfall Roundup

In August, rainfall was ‘Below Average’ for much of the southern half of Australia (Fig. 1). Notable exceptions include the eastern coastline of Victoria, the southern coastline of New South Wales, northern parts of Queensland as well as northern areas of the Northern Territory where rainfall was ‘Above Average’ (Fig. 1).

Over the last three months much of Australia has recorded ‘Average’ rainfall however some areas including central parts of Western Australia have received ‘Below Average’ rainfall and parts of south west Western Australia, eastern New South Wales as well as a large area of the Northern Territory and Queensland recorded ‘Above Average’ rainfall (Fig. 2).


Figure 1. Rainfall deciles for August 2021.
Figure 2. Rainfall deciles for June 2021 to August 2021.

Rainfall Forecast

The BoM’s ACCESS model predicts that rainfall in September is likely to be ‘Above Average’ for much of Australia (Fig. 3). However, western parts of Western Australia and north west Tasmania are likely to be ‘Below Average’ and the remainder of Tasmania, northern Queensland and parts of inland Western Australia have equal chances of ‘Above’ or ‘Below Average’ rainfall (Fig. 3).

For the three-month forecast, September to November, rainfall is likely to ‘Above Average’ for much of the eastern two-thirds of Australia extending into south-east Western Australia (Fig. 3). Parts of western Tasmania and the western coastline of Western Australia are however likely to receive ‘Below Average’ rainfall and the rest of Western Australia has equal chances of rainfall being ‘Above’ or ‘Below Average’ (Fig. 3).

At this time of year accuracy for the three-month forecast is moderate to high for most of Australia except for central parts of Western Australia where accuracy is low (Fig. 3). 

Figure 3. Australian rainfall outlook for September to November 2021.

Temperature Roundup

Maximum temperatures in August were ‘Above Average’ for most of Australia with the northern tips of the Northern Territory and Western Australia recording highest on record temperatures (Fig. 4). Minimum temperatures were ‘Average’ to ‘Above Average’ across much of Australia however a few areas in the Northern Territory, Western Australia, eastern South Australia and northern New South Wales were ‘Below Average’ (Fig. 5).

Figure 4. Maximum temperature deciles for August 2021.
Figure 5. Minimum temperature deciles for August 2021.

Temperature Forecast

The BoM’s ACCESS model forecast predicts that over the next three months maximum temperatures are likely to be ‘Above Average’ for northern Australia as well as all of Tasmania and southern parts of Victoria and coastal New South Wales (Fig. 6). For a large area stretching from Western Australia, to New South Wales and up into southern Queensland there is an increased chance of ‘Below Average’ maximum temperatures (Fig. 6).

For minimum temperatures, much of Australia is likely to be ‘Above Average’ for the next three months, except for south west Western Australia where they are likely to be ‘Below Average’ (Fig. 7).

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 temperatures, accuracy is moderate to high for much of Australia excluding parts of Queensland and the Northern Territory where accuracy is low (Fig. 7). 

Figure 6. September to November 2021 maximum temperature outlook.
Figure 7. September to November 2021 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.

Leave a Reply