The US Climate Prediction Center has just sounded the alarm. La Niña is back.

Cooler waters have taken hold across the Pacific Ocean, and experts overseas say this global weather pattern is set to stick around for months. But, the Bureau of Meteorology has yet to echo the call, so what does this mean for Australians and the upcoming summer?

La Niña is a weather phenomenon that brings cooler ocean temperatures in the Pacific and typically results in increased rainfall and more frequent storms across much of Australia. It is the counterpart to El Niño, which causes drier conditions.

Australians will have no trouble remembering the three consecutive La Niña events from 2020 to 2022, -- an unusual occurrence known as a "triple-dip" -- which led to record-breaking rainfall in many areas, causing widespread flooding, particularly in eastern states like Queensland and New South Wales.

Experts warn that the impacts of La Niña are becoming more pronounced due to climate change, making it crucial to prepare for more intense weather cycles in the future.

The US Climate Prediction Center (CPC) announced late last week that a La Niña event is officially underway. According to the advisory, the pattern is expected to last through the end of the year and into early 2026, before likely returning to neutral conditions between January and March next year.

In simple terms, La Niña occurs when the surface waters in the central Pacific Ocean become noticeably cooler than usual -- at least half a degree below average -- and stay that way for several months. But it's not just about ocean temperatures. To confirm a true La Niña, scientists also look for changes in the atmosphere above the Pacific, such as stronger trade winds and shifts in rainfall patterns.

The CPC says both of these signs -- cooler ocean waters and the expected atmospheric response -- are now in place. In other words, the ocean and atmosphere are working together in a way that indicates La Niña conditions.

The US and Australian weather agencies don't currently see eye to eye on whether La Niña has arrived. While the US Climate Prediction Center (CPC) has officially declared that La Niña conditions are underway, Australia's Bureau of Meteorology (BoM) is holding off, saying the climate pattern remains in a neutral phase for now.

That's because the BoM uses slightly stricter criteria than the CPC. It requires cooler-than-normal ocean temperatures in the tropical Pacific to be both stronger and last longer before making a formal declaration. So even though the Pacific Ocean meets the US definition of La Niña, it hasn't yet crossed the Australian threshold.

The BoM says the El Niño-Southern Oscillation, or ENSO, is still neutral. Its modelling suggests the Pacific might briefly reach La Niña levels during spring but will probably shift back to neutral by summer. In other words, if La Niña does develop by Australia's standards, it's expected to be weak and short-lived.

If La Niña were to be declared in Australia, it would mean an increased chance of wetter-than-normal conditions over summer, when the "strongest impacts" of the weather events are felt.

When a moderate or strong La Niña develops during late spring or early summer, it usually brings more cloud cover, increased rainfall, and cooler daytime temperatures across much of Australia -- especially in the north, centre and east. But when La Niña is weak or only borderline, its effects on the weather become much harder to predict.

At the moment, the Pacific Ocean is showing clear signs of a La Niña-like setup. However, forecasts suggest it will likely be mild and short-lived, meaning it probably won't have a major impact on Australia's weather this season.

Instead, other climate influences are expected to play a bigger role. These include the Indian Ocean Dipole (IOD), the Southern Annular Mode (SAM), and unusually warm sea surface temperatures around Australia. For the latest rainfall and temperature forecasts, it's best to check the Bureau of Meteorology's most recent climate outlook maps.

Just weeks ago a negative Indian Ocean Dipole (IOD) was announced by the Bureau of Meteorology, which resulted in predictions of a wetter than average summer.

What La Niña update means for Aussie weather over spring and summer