The BOM this week updated its outlook from 'La Niña WATCH' to 'La Niña ALERT' meaning it is highly likely the spring will be wetter than average for much of the eastern Australian mainland between September and November.

The outlook reflects a range of climate drivers including a negative Indian Ocean Dipole (IOD) event and warmer than average waters around Australia.

La Niña refers to changes in sea surface temperatures in the tropical Pacific Ocean, with waters in the eastern Pacific being cooler than normal, and waters in the western tropical Pacific being warmer than normal.

Trade winds strengthen, increasing the water moisture in the air, which usually brings rainfall to eastern and central Australia and a wetter start to the northern wet season.

The BOM says with wet soils, high river levels and full dams, and the outlook for above average rainfall, an elevated risk of flooding remains for eastern Australia.

Should a La Niña event be established in the Pacific Ocean, the wet conditions should  persist into summer.