THE CLIMATE KELPIE BLOG: What’s predicted in December?
The La Niña event continues in the tropical Pacific Ocean. Most models are continuing to suggest that it will likely peak in December but persist until the end of February 2021. There are also warmer than normal sea surface temperatures to the north of Australia which look likely to persist and are helping to contribute towards the forecast for ‘Above Average’ rainfall across much of Australia over the summer months.
The Indian Ocean Dipole (IOD) has now remained neutral for some time and isn’t expected to change from this state anytime soon. Therefore, the IOD is not likely to influence Australia’s rainfall over summer 20/21. The Indian Ocean remains warmer than normal evaporating greater moisture.
The Southern Annular Mode (SAM) on the other hand, whilst currently neutral looks like it may return to positive values over the next week or so. During a La Niña event, a positive SAM will typically enhance the wet signal in parts of eastern Australia except for western Tasmania where it is often drier.
As a result, the overall outlook for December to February is for ‘Above Average’ rainfall across much of Australia except for the west coast of Tasmania where ‘Below Average’ rainfall is likely. In terms of temperatures, minimums are likely to be ‘Above Average’ across most of Australia and maximums are likely to be ‘Above Average’ across parts of the southeast and far west of Australia as well as along the coastline of northern Australia. ‘Below Average’ maximum temperatures are however expected in the north west of Western Australia as well as along the south coast of Western Australia into South Australia.
In November, much of the eastern two thirds of Australia received ‘Below Average’ rainfall (Fig. 1). However, some regions did receive ‘Above Average’ rainfall most notably the north west and south west of Western Australia and a few small pockets in Victoria, New South Wales and Queensland (Fig. 1). For the last three months much of Australia has received ‘Average’ rainfall, however some regions experienced ‘Below Average’ rainfall including south west Tasmania and south east Queensland and other areas recorded ‘Above Average’ rainfall including South Australia, western New South Wales, south west Victoria, the northern tip of Queensland and north west Western Australia (Fig. 2).
The BoM’s ACCESS model predicts that December is likely to deliver ‘Above Average’ rainfall across much of Australia except for western Tasmania, the south west of Victoria and a pocket in central Australia where there are equal chances of rainfall being ‘Above’ or ‘Below Average’ (Fig. 3). For the three-month forecast, December to February, rainfall is expected to follow a similar pattern with ‘Above Average’ rainfall likely across most of Australia excluding south west Tasmania where ‘Below Average’ rainfall is forecast and an area around Darwin which has equal chances of it being ‘Above’ or ‘Below Average’ (Fig. 3).
At this time of year accuracy for the three-month forecast is high along parts of Western Australia’s coastline, moderate across much of Australia and low for much of the Northern Territory into Queensland and Western Australia as well as northern New South Wales, south west Tasmania and northern and southern parts of South Australia (Fig. 3).
Maximum temperatures in November were ‘Above Average’ across much of Australia except for the south west of Western Australia where they were ‘Below Average’ (Fig. 4). Minimum temperatures were also ‘Above Average’ over most of Australia however, the far south west tip of Western Australia and a small pocket in northern Queensland were ‘Below Average’.
The BoM’s ACCESS model forecast suggests that over the next three months maximum temperatures are likely to be ‘Above Average’ along the west coast of Western Australia, the northern coastlines of the Northern Territory and Queensland, along the Queensland and New South Wales border, all of Victoria and Tasmania as well as parts of New South Wales and South Australia (Fig. 6). In contrast, north west Western Australia as well along the southern coastline of Western Australia into South Australia are likely to experience ‘Below Average’ maximum temperatures (Fig. 6). For minimum temperatures, most of Australia is likely to be ‘Above Average’ for the next three months (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 large area in the Northern Territory and across into Queensland (Fig. 6). For minimum temperature, accuracy is moderate to high across most of Australia except for a large area of the Northern Territory and Queensland, as well as a small pocket in Western Australia (Fig. 7).
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