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

Posted by BCG on 13th October 2021

The negative Indian Ocean Dipole (IOD) is weakening, with the latest IOD values falling outside of the negative threshold. However, the waters to the North of Australia are still warmer than normal which is helping to generate moisture in the region and is likely to contribute towards ‘Above Average’ rainfall for parts of Australia.

In terms of the El Niño -Southern Oscillation (ENSO), this climate driver remains neutral, however recent cooling in the tropical Pacific Ocean has raised the chances of a La Niña threshold being met this year. As a result, the BoM has moved its ENSO Outlook Status to La Niña WATCH, which in the past has meant that the chances of a La Niña forming is around 50% (double the normal odds). Regardless of a La Nina forming or not this activity on the Pacific Ocean is also likely contributing to the increased chances of ‘Above Average’ rainfall for much of eastern and northern Australia.

Our shorter-term climate driver, the Southern Annular Mode (SAM) is currently neutral but forecast to be positive for much of October to December. A positive SAM during spring/summer typically brings ‘Above Average’ rainfall to eastern parts of Australia, except western Tasmania.  

The Madden-Julian Oscillation (MJO) is currently over PNG and is moderate. It is expected to fall to weak in the coming fortnight as it leaves Australia for the western Pacific. The MJO in a moderately strong phase to the north or Australia increases the chances of rainfall over southern Australia. 

Therefore, the overall outlook for October to December is for rainfall to likely be ‘Above Average’ for much of Australia but ‘Below Average’ for western parts of Tasmania. In terms of temperatures, maximums are likely to be ‘Above Average’ across northern Australia extending down into the west of Western Australia and south-east of Australia except for parts of the east and south-west where ‘Below Average’ minimums are likely. Minimum temperatures are forecast to be ‘Above Average’ for most parts of the country except for parts of south-east Western Australia where the chances are equal for ‘Above’ or ‘Below Average’ temperatures.

Rainfall Roundup

In September, rainfall was ‘Above Average’ for much of eastern Australia and the Northern Territory (Fig. 1). There were however areas that missed out, including southern parts of Western Australia and South Australia as well as parts of north-east Tasmania, coastal New South Wales, south-east Queensland and northern parts of the Northern Territory (Fig. 1).

Over the last three months a large part of Western Australia flowing into South Australia has now received ‘Below Average’ rainfall (Fig. 2). Rainfall deficiencies are also starting to show up in eastern Tasmania. The remainder of Australia has recorded ‘Average’ rainfall except for south-west Western Australia, western Tasmania, eastern Victoria, central New South Wales, northern Queensland and parts of the Northern Territory where totals were ‘Above Average’ (Fig. 2).

Figure 1. Rainfall deciles for September 2021.
Figure 2. Rainfall deciles for July 2021 to September 2021.

Rainfall Forecast

The BoM’s ACCESS model predicts that rainfall in October is likely to be ‘Above Average’ for the eastern two-thirds of Australia (Fig. 3). Western parts of Tasmania are however likely to be ‘Below Average’ as well as some parts of Western Australia. The rest of Western Australia looks likely to have equal chances of ‘Above’ or ‘Below Average’ rainfall (Fig. 3).

For the three-month forecast, October to December, rainfall is likely to be ‘Above Average’ for much of Australia (Fig. 3). Parts of western Tasmania are however likely to be ‘Below Average’ and much of the Pilbara region of Western Australia have 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 Australia and western Western Australia where accuracy is low (Fig. 3). 

Figure 3. Australian rainfall outlook for October to December 2021.

Temperature Roundup

Maximum temperatures in September were ‘Average’ to ‘Above Average’ across much of Australia however, a few parts of Australia were ‘Below Average’ including small areas in Queensland, the Northern Territory and Western Australia (Fig. 6). Minimum temperatures were also ‘Average’ to ‘Above Average’ across much of Australia however a few areas in Western Australia, South Australia, New South Wales and Queensland were ‘Below Average’ (Fig. 5).

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

Temperature Forecast

The BoM’s ACCESS model predicts that over the next three months maximum temperatures are likely to be ‘Above Average’ for coastal parts of northern Australia as well as all of Tasmania and southern parts of Victoria into South Australia (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 eastern parts of Western Australia where they have an equal chance of being ‘Above’ or ‘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, except for a very small pocket in north-east Western Australia where accuracy is low (Fig. 6). For minimum temperatures, accuracy is moderate to high for much of Australia excluding a large area of the Northern Territory, parts of north-east Western Australia and a small pocket on the Queensland/New South Wales border where accuracy is low (Fig. 7). 

Figure 6. October to December 2021 maximum temperature outlook.
Figure 7. October to December 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.

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