Australia Weather News

Australia's key drivers of weather variability are stacking up to produce another wet, severe-weather season, with an increased risk of flooding, thunderstorms and cyclones.

The forecast is based off multiple indicators, including the potential for a late-forming La Niña — whose appearance in 2025 would mark the fifth event in the space of six years, a frequency only previously observed once since 1900.

While an active season amplifies the risk of severe weather, it could dampen the fire risk in most states and offers hope of additional drought relief across Victoria, South Australia and Tasmania.

Negative IOD and now possibly La Niña's return

Long-range outlooks favour above-average rain this spring and summer thanks to a multitude of broadscale influences:

While three of the four influences are basically set, La Niña's arrival and influence is less certain.

The key monitoring index for the state of the Pacific is called Niño3.4, which is a calculation of the temperature relative to the average in a region of the basin along the equator.

The latest value of Niño3.4 is -0.62 degrees Celsius, just shy of the Bureau of Meteorology's (BOM) La Niña threshold of -0.8C, although already below the -0.5C yardstick used by the National Oceanic and Atmospheric Administration (NOAA).

However, the ocean is only one half of La Niña.

For a fully-fledged event, the atmosphere needs to respond — otherwise we would see no changes in the actual weather.

And while some atmospheric indicators, like trade wind strength, do reflect an emerging La Niña, others, including the traditional Southern Oscillation Index are currently around +5, still below typical La Niña levels of at least +7.

Though La Niña territory has not been reached yet, the indicators are slowly trending in that direction, and modelling is tipping further cooling of the Pacific during the coming weeks.

Under the scenario, the transition to La Niña continues.

Its impact on Australia's weather is somewhat uncertain due to a late arrival compared to a typical winter onset and a subsequent relatively weak and short event.

What is clearer though is considering the holistic state of Australia's weather influences, the odds are strongly stacked against a dry severe weather season — especially across eastern states.

For areas of south-east Australia, a wet warm season would bring further relief from the severe rain deficits which have accumulated since early 2024.

However for the drought to end, several seasons of above rain are required and the dry environment will maintain a heightened fire risk if heavy rains do not arrive.

For most remaining corners of Australia, high soil moisture from recent rain combined with the wet forecast has reduced the fire risk relative to drier years.

Enhanced risk of cyclones and thunderstorms

The additional ocean heat and possibility of lower pressure supports a forecast of above average thunderstorms and cyclones.

The Australian region averages 10 tropical cyclones per year, although that figure has dropped to a fraction below nine this century thanks to climate change.

An early prediction from the well-renowned European Centre for Medium-Range Weather Forecasts (ECMWF) model indicates closer to 11 systems this season, which if accurate would make it the equal third-busiest season since 2000.

The model picks six will become severe (category 3 or above), again slightly above the long-term average of five severe tropical cyclones.

Similarly, the additional moisture could help to fuel more thunderstorms.

The thundery outlook is especially true for the eastern seaboard where the BOM's modelling predicts offshore waters to remain abnormally warm — the perfect recipe for stormy afternoons in cities like Brisbane and Sydney.

High humidity but possibly cooler days

Australia's four hottest summers since 1900 have all occurred in the past seven years. However, the presence of additional cloud could moderate the record summer heat of the past few years.

Despite a reduced risk of unprecedented heat, the BOM's modelling still picks above median temperatures for most of the country during the coming months.

Global models also tip warmer than normal seasons ahead, but again not at the peak severity of the past few years.

While extra cloud may take the edge off the afternoon heat, its presence will have the opposite effect on overnight temperatures and humidity — so expect muggy nights and sweaty days, which could mean this summer feels warmer than raw temperature data suggests.

Wet climate drivers inordinately active

The repeated occurrence of wet climate drivers during recent years is almost becoming monotonous and the past five severe weather seasons (October to April) have all brought above-average rain (when averaged across the entire country).

This year's negative IOD is the third since 2021, well above the climatological frequency of one every five years.

La Niña dominance is even more pronounced — on the fringe of five episodes in six years against a long-term average of one every four years.

As a result, most of Australia since 2020 has observed well above average rain, and record falls have soaked parts of NSW, far-southern Queensland and the tropics.

The only other period which has seen La Niña at this frequency was between 1970 and 1975, also an exceptionally wet period in our history.

Despite the odds favouring rain, Australia's western and southern coastline has missed out in recent years, largely due to a shift in the broadscale path of high-pressure systems and cold fronts — another background influence of a global warming.