Sea surface temperature observations from the past two weeks suggest that El Niño could be rapidly emerging in the tropical Pacific Ocean.
Computer models have been hinting at the possibility of a 2026 El Niño event for the past three months, with the Bureau’s modelling predicting in January that El Niño could develop by winter.
Things now appear to be moving faster than anticipated, with ocean temperatures in the tropical Pacific Ocean rapidly warming towards El Niño thresholds in the past couple of weeks.
Ocean temperatures inside the key monitoring region for El Niño - an area known as the Niño3.4 region – have warmed rapidly this month, rising by 0.5°C in the last two weeks and 0.3°C in just one week.
El Niño occurs when sea surface temperatures in the Niño3.4 region are warmer than average for several consecutive months. In Australia, the El Niño threshold is 0.8°C warmer than the long-term average (taking the background warming signal from climate change into account).
The latest weekly Niño3.4 index value, measured in the week ending on April 26, 2026, was 0.23°C above average. Just two weeks ago this index was sitting 0.27°C below average and just over two months ago, it was at -0.87°C, below the threshold for La Niña.
Image: Relative weekly Niño3.4 index during the last few years. Source: Weatherzone.
A rapidly rising Niño3.4 temperature can be a sign that El Niño is emerging in the Pacific Ocean. However, this ocean warmth will need to intensify further and be sustained for several months to qualify as an official El Niño event.
READ MORE: What does a 'super El Niño' mean for Australia's weather?
Another important part of El Nino is the atmospheric response to the oceanic warming. For El Niño to become established in 2026, the ocean and atmosphere need to become coupled and reinforce each other.
The atmosphere is starting to show signs of an El Niño pattern, with the 30-day Southern Oscillation Index (SOI) – a measure of atmospheric pressure difference across the tropical Pacific – dipping below –10 in the past week. This is well below the El Niño threshold of –7, however, these negative values will need to be sustained for at least several weeks to qualify as an El Niño signal. Furthermore, easterly trade winds over the western Pacific Ocean are weakening, which is another sign of a developing El Niño.
It is too early to say that El Niño has arrived, but the ocean and atmosphere are showing clear signs that it could be rapidly emerging as we head into the final month of autumn.