Australia on watch for El Niño as ocean temperatures surge

There are fresh signs an El Niño weather pattern is edging closer, with forecasters tracking a spike in Pacific temperatures that could trigger the climate driver this winter.

If this system develops, it could put a warmer and drier season on the cards, with less rainfall, milder days and reduced snow cover.

The Climate Council warns that an upcoming El Niño would hit an atmosphere already 1.5°C warmer than pre-industrial levels due to fossil fuel pollution. This extra trapped heat will supercharge the system, making future El Niño cycles progressively hotter.

According to the Bureau of Meteorology, the El Niño–Southern Oscillation (ENSO) remains neutral for now. Still, ocean temperatures have risen, and all major climate models point to further warming in the months ahead.

While Australia’s weather is influenced by multiple climate drivers, the ENSO has one of the strongest influences on the country’s year-to-year climate variability.

It’s determined by water temperatures in the central and eastern tropical Pacific Ocean and alternates between El Niño, characterised by sustained ocean warming, and La Niña, marked by months of ocean cooling.

The latest update shows the key Niño 3.4 region of the Pacific − used to monitor El Niño and La Niña events − has warmed by about 0.2 degrees in the past fortnight and by 1.3 degrees since early March.

While that region has not yet reached the Bureau’s El Niño threshold, a large pool of unusually warm water sitting beneath the ocean surface is expected to fuel additional warming as winter gets underway.

For those wondering if an El Niño declaration is imminent, the short answer is not yet.

Sea surface temperatures are forecast to reach El Niño levels during early winter, but meteorologists say an official declaration also requires the atmosphere to respond. That means broad-scale changes to trade winds, air pressure and cloud patterns across the tropical Pacific.

Those atmospheric indicators are still within the neutral range, although recent observations suggest they are moving toward El Niño conditions.

As of May 24, the Southern Oscillation Index (SOI) − a measure used by forecasters − sat at -13.4 over 30 days, a reading commonly associated with El Niño-like conditions.

The Bureau said the atmosphere and ocean are increasingly aligning, but more evidence is needed before an event can be officially declared.

In April, Weatherzone meteorologists said the Pacific was already displaying the strong early warning signs typically observed at this time of year.

One of the clearest signals is a vast pool of exceptionally warm water lying at depths of 50 to 250 metres beneath the surface of the tropical Pacific.

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In some locations, temperatures within that subsurface pool are sitting over six degrees above average.

As this warmth rises towards the surface over coming weeks and months, it is expected to help push Pacific Ocean temperatures into El Niño territory.

Global forecast models are also unusually in sync.

Forecast confidence is often lower during autumn due to what scientists call the “autumn predictability barrier”, a period when forecasting ENSO events becomes more difficult.

Although this year, model agreement remains strong, with all major forecasting systems projecting continued warming across the tropical Pacific.

There is still uncertainty around how intense the event may become.

The Bureau’s modelling suggests the developing El Niño will be at least moderate, but there’s still a chance it could turn into a strong event later in 2026.

Weatherzone reports some international modelling is even raising the prospect of a so-called “super El Niño”, although current forecasts suggest that outcome remains far from guaranteed.

Even if El Niño is declared, experts stress it does not automatically determine Australia’s weather.

El Niño is only one of several climate drivers influencing rainfall, temperatures and weather systems across the nation.

In the past, El Niño events have increased the likelihood of below-average winter and spring rainfall across much of the country, alongside warmer daytime temperatures in many southern and eastern regions.

They can also heighten drought risk, raise the chance of dangerous fire weather later in the year and reduce alpine snow depths.

However, meteorologists caution that no two El Niño events behave the same way.

The Indian Ocean Dipole is currently neutral and could also play a role in Australia’s weather later this year, while regional sea surface temperatures around the continent remain an important factor.