The Bureau of Meteorology has declared a La Niña event is under way in the Pacific Ocean and communities in eastern Australia should be prepared for above-average rainfall over spring and early summer.
Bureau of Meteorology head of long-range forecasts Dr Andrew Watkins said the bureau's three-month climate outlook showed a high chance of above average rainfall for most of the eastern half of the Australian mainland and eastern Tasmania.
“During La Niña events, waters in the eastern tropical Pacific Ocean are cooler than normal, and waters in the western tropical Pacific Ocean warmer than normal,” Dr Watkins said.
“This causes changes in wind, cloud and pressure patterns over the Pacific. When this change in the atmosphere combines with changes in ocean temperature, it can influence global weather patterns and climate, including increasing rainfall over large parts of Australia”.
Dr Watkins said while La Niña criteria had been met, most models forecast this event to be weak to moderate in strength, likely to peak during spring and ease during summer.
"La Niña is not the only driver influencing this wet outlook. To our west, a significant negative Indian Ocean Dipole event is underway. We expect the IOD influence will reduce in late spring or early summer,” Dr Watkins said.
“The Southern Annular Mode is also in a positive phase, and likely to remain positive into summer. Positive SAM during summer pushes weather systems south, which increases the chance of rain in New South Wales, eastern Victoria and southern parts of Queensland.”
Dr Watkins said all these climate influences pushed Australia's climate towards a wetter phase, and together had shaped the outlook for the coming months that showed more than 80 per cent chance of above average rainfall for many parts of the eastern half of Australia.
With catchments already wet, the flood risk remains, particularly for eastern Australia.
The Bureau encourages communities to keep up to date with the latest forecasts and warnings on the bureau's website and BOM Weather app.