BoM estimates that a La Niña, usually associated with wetter-than-normal years in eastern Australia, is now looking “more likely than not”.

Dr Andrew Watkins, Manager of the Bureau’s Climate Prediction Services, said that if recent trends in Pacific climate patterns continue, computer model forecasts show that a La Niña event will be established before the end of winter.

However, it is still possible that recent trends may stall without La Niña thresholds being reached. Even if this did occur, parts of Australia may still experience wetter than average conditions, especially if the Southern Oscillation Index (SOI) remains positive.

Historically, La Niña events have often, but not always, brought above average rainfall to much of Australia, particularly inland eastern and northern regions.

Floods hit NSW and Queensland in the event of 1998, while the La Niña of 1988-89 saw flooding also occur in SA and Victoria.

Night time temperatures are usually warmer than average, and tropical cyclone risk for northern Australia increases during La Niña events.

The main feature of a La Niña is a broad region of colder than average water along the eastern equatorial Pacific.

The surface of the equatorial Pacific is currently cooler than average in some areas, while the Southern Oscillation Index (SOI), which is often indicative of pressure patterns over Australia, has been positive since April.

The current value of the SOI is around +6.

Weekly updates on the situation will be posted at the BoM’s ‘ENSO Wrap-Up’ webpage at www.bom.gov.au/climate/enso