The Bureau of Meteorology's Winter 2022 Climate Outlook shows a slowly weakening La Nina is one climate factor influencing above average winter rainfall for most of central and eastern Australia in coming months.
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Parts of south-western Australia and south-western Tasmania are likely to have below average rainfall this winter.The Outlook predicts the unusually wet conditions for inland parts of NSW, South Australia, Queensland and the Northern Territory are likely to be in the top 20% of wettest winters.
With Northern Australia's dry season starting in May, it only takes a small amount of extra rain to be above average at this time of year.With already saturated catchments in south-eastern Australia, the winter rain extends the flood risk for these regions.
The flood waters in low lying areas in Queensland and NSW will slowly move inland towards South Australia over coming months.There is an above 80% chance of unusually high winter temperatures in coastal, south-western and northern parts of Western Australia, coastal northern areas of the Northern Territory and Queensland, south-eastern NSW, southern and eastern Victoria, and all of Tasmania.
A large section of central Australia has an increased chance of unusually low winter daytime temperatures, in the coolest 20% of past winters. This extends from Western Australia's eastern area through central Australia into the eastern states.Warmer than average nights are likely almost everywhere - with at least an 80% chance of higher minimum temperatures for most of Australia.
The winter outlooks reflect several climate influences, including a developing negative Indian Ocean Dipole, a slowly declining La Nina in the Pacific Ocean and warmer than average waters around northern Australia.
The Indian Ocean Dipole (IOD) is currently neutral. However, the IOD index has become more negative over the past fortnight. All climate model outlooks surveyed suggest a negative IOD may develop in the coming months. While model outlooks have low accuracy at this time of year and some caution should be taken with IOD outlooks, there is strong forecast consistency across international models. Outlook accuracy for the IOD begins to significantly improve during June. A negative IOD increases the chances of above average winter-spring rainfall for much of Australia. It also increases the chances of warmer days and nights for northern Australia.
BOM has released a formal record of the extreme rainfall and flooding that occurred in south-east Queensland and eastern NSW in February and March this year. In the last week of February, parts of south-east Queensland and north-east NSW had rainfall 2.5 times their monthly average with some regions recording more than five times their monthly average.
In parts of northern NSW, flood levels broke previous records. Wilsons River in Lismore peaked at a record high level, estimated to be 14.4 m on 28 February. The previous record was 12.27 m in February 1954. In recent decades, there has been a trend towards a greater proportion of high-intensity, short-duration rainfall events, especially across northern Australia.