Pacific Ocean subsurface water now 8°C above normal – what this means for El Niño

A large pool of exceptionally warm water sitting below the surface of the eastern tropical Pacific Ocean is laying the foundation for a prolonged and potent El Niño in the second half of 2026.

El Niño occurs when sea surface temperatures in the central and eastern tropical Pacific Ocean are above average for several consecutive months and there is an associated response in the overlying atmosphere.

But while sea surface temperatures are a key metric used to define El Niño, what’s happening beneath the surface is also an important indicator for how El Niño will develop in the coming weeks and months.

When unusually warm water sits below the surface of the tropical Pacific Ocean, it typically rises towards the surface, which can help sustain or intensify El Niño.

Warm pool sitting beneath tropical Pacific Ocean surface

A pool of abnormally warm water is currently lying beneath the surface of the central and eastern tropical Pacific Ocean. In one region about 50 to 100 m below the equator in the eastern Pacific, the water is more than 8°C above average for this time of year.

Sea surface temperature anomalies in the Pacific Ocean on July 4, 2026
Image: Cross section of water temperature anomalies below the equator, with the Pacific Ocean sitting at the centre of the image between the two inner-most grey bars. The y-axis on the left shows depth in metres. Source: NOAA

This slab of anomalously warm water below the surface is likely to cause El Niño to gain strength in the coming months.

According to the latest modelling from the Bureau of Meteorology, sea surface temperature anomalies in the central and eastern tropical Pacific Ocean will continue to climb between July and October, before reaching a peak sometime between October and December. Based on this forecast, the current El Niño event will become very strong and will likely persist well into the first half of 2027.

Image: Relative Nino3.4 forecast, showing El Niño likely to strengthen in the coming months. Source: Bureau of Meteorology.

What does this mean for Australia's weather in the coming months?

El Niño typically makes the following weather more likely in Australia:

Reduced rainfall during winter and spring, particularly over the eastern half of Australia.

Above average daytime temperatures in southern and southeastern Australia from winter to summer.

Increased winter and early-spring frost risk in southeastern Australia due to clearer skies.

Less snow, including a lower peak snow depth and shorter snow season.

Delayed monsoon onset in northern Australia.

Increased risk of fires.

However, it is important to point out that no two El Niño events are the same and neither are their impacts.