La Nina fading, but flood threat remains

31 January 2023

The flood-inducing La Nina weather system is continuing to ease in the tropical Pacific, but the threat of increased rainfall still hangs over much of Australia.

The Bureau of Meteorology says today that while ocean temperatures have dropped from La Nina thresholds “the atmosphere has yet to respond, and remains La Nina-like”, increasing the chances of above-average rainfall for northern and eastern Australia during summer.

This is the third La Nina in a row, and severe east coast floods have occurred in February and March in the past two years.

However, a return to neutral conditions is expected next month, and this should last until at least mid-autumn.

Some experts predict that an El Nino will follow, flipping the risk to heatwaves and bushfires next summer, but the bureau says long range forecasts made during summer have low accuracy and “outlooks that extend past autumn should be viewed with caution”.

The Southern Annular Mode (SAM) is currently strongly positive, but is anticipated to ease over the coming fortnight and then remain neutral over the remainder of February.

During summer, a positive SAM is typically associated with an increased chance of above average rainfall for eastern NSW, eastern Victoria, and north-east Tasmania, and below average rainfall for western Tasmania.

The Madden–Julian Oscillation (MJO) is currently moderate to strong and over the eastern Indian Ocean.

“Most models expect it to move across the Maritime Continent and towards the western Pacific in the coming week, with a possible decline in strength,” the Bureau says.

“While in the Maritime Continent, the MJO may increase the chance of an active monsoon period in northern Australia.”