The La Niña event that developed in late September/early October is well under way with the sea surface temperatures in the tropical Pacific Ocean remaining cool and the trade winds stronger than normal. Most models are suggesting that the La Niña will likely peak in December and could eventuate into a strong but short-lived event. A La Niña typically increases the chances of ‘Above Average’ rainfall across much of Australia during spring and summer.
Unlike the Pacific Ocean, the early signs of possible action in the Indian Ocean have since dissipated with the Indian Ocean Diploe (IOD) looking likely to remain neutral for the rest of 2020, however the warmer waters to the north of Australia may be favourable for enhancing rainfall over Australia.
In addition to the above, a positive Southern Annual Mode (SAM) may also contribute to enhancing rainfall over the coming months. SAM is currently strongly positive and predicted to stay positive for the next month. It is also predicted to be positive over summer. During a La Niña event, a positive SAM will typically enhance the wet signal from the La Niña in parts of eastern Australia except for western Tasmania which is often drier.
As a result, the overall outlook for November to January is for ‘Above Average’ rainfall across much of Australia except for south west Tasmania where ‘Below Average’ rainfall is likely. In terms of temperatures minimum are likely to be ‘Above Average’ across most of Australia and maximums are likely to be ‘Below Average’ along coastal New South Wales and the southern coastline of Western Australia with most other areas of Australia likely to experience ‘Above Average’ maximum temperatures.
In October, much of Australia received ‘Above Average’ rainfall (Fig. 1). However, some regions were not so fortunate, most notably south west Western Australia (Fig. 1). The rain that fell during October has greatly contributed to increasing the area of Australia that has now received ‘Above Average’ rainfall for the last three months (Fig. 2). The south west of Western Australia and a few isolated pockets in the other states are exceptions, continuing to receive ‘Below Average’ rainfall (Fig. 2).
The BoM’s ACCESS model predicts that November is likely to deliver ‘Above Average’ rainfall across much of Australia except for south west Tasmania where ‘Below Average’ rainfall is likely and parts of central Australia and Western Australia where they have equal chances of rainfall being ‘Above’ or ‘Below Average’ (Fig. 3). For the three-month forecast, November to January, 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 (Fig. 3).
At this time of year accuracy for the three-month forecast is moderate to high across Australia except for most of the Northern Territory and parts of New South Wales, South Australia, Queensland and Western Australia where accuracy is low (Fig. 3).
Maximum temperatures in October were ‘Below Average’ through central Australia but ‘Above Average’ elsewhere including along parts of northern Australia, the central east coast of Australia and parts of Western Australia (Fig. 4). Minimum temperatures were ‘Above Average’ across much of Australia except for an area in Western Australia and a couple of pockets in central Australia where they were ‘Below Average’ (Fig. 5).
The BoM’s ACCESS model forecast suggests that over the next three months maximum temperatures are likely to be ‘Above Average’ across central Australia, Tasmania, most of Victoria, the northern Australia coastline and parts of Western Australia. In contrast, coastal New South Wales and the southern coastline of Western 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 small pocket of the Northern Territory (Fig. 6). For minimum temperature over the next three months, accuracy is moderate to high across most of Australia except for a large area of the Northern Territory and into northern Western Australia, as well as a small pocket on the Queensland and New South Wales border (Fig. 7).
Climate and Water Outlook Videos
The Bureau of Meteorology releases regular outlook videos, covering all this information. Watch the most recent video below.