The United States Climate Prediction Center has an El Niño Watch in place, and in its mid-May 2026 discussion it put the odds of El Niño emerging in the tropical Pacific by mid-year at about 82 per cent, rising to 96 per cent for the Northern Hemisphere winter of 2026-27. After the strong El Niño of 2023-24 and the weak La Niña that followed, a return is now the expected path rather than one possibility among several. The objective model plume run by the International Research Institute for Climate and Society is firmer still, assigning El Niño roughly a 98 per cent chance for the May to July period.

The ocean signal itself is still modest, and the two groups were reading it slightly differently in real time. The Climate Prediction Center’s latest weekly Niño 3.4 value was plus 0.4 degrees Celsius, while the IRI’s OISSTv2 measure had recent weekly readings near plus 0.9, a gap the IRI attributes to differences between the sea surface temperature datasets used in real-time analysis.

What is far less settled is how strong it gets.

What the forecasts actually say about strength

The arrival and the amplitude are two different questions, and the models are much more confident about the first. In its May discussion the Climate Prediction Center was clear about the event forming but much less definite about how strong it becomes. It said no single strength category exceeded a 37 per cent chance, and described substantial uncertainty in the peak strength. The outlook leaves a wide range open, including a strong or very strong event, but the Center’s own emphasis is on uncertainty rather than confidence.

It is explicit on a related point that often gets lost: a stronger El Niño does not guarantee strong impacts, it only makes certain ones more likely.

Why strength is harder to call than arrival

Forecasts issued in the Northern Hemisphere spring are the least reliable of the year, because the ocean-atmosphere system is in transition and small differences compound. The May outlooks sit just past that window, which is part of why confidence in the event forming has firmed since the more cautious readings earlier in the year.

The amplitude is the harder part. The strongest El Niño events in the record are marked by tight coupling between ocean and atmosphere through the summer, with the equatorial trade winds weakening as sea surface temperatures rise and reinforcing the warming. Whether that feedback locks in this year is not yet known. The European Centre for Medium-Range Weather Forecasts noted in its April assessment that the 2026 signal looked stronger and more focused than the comparable forecast in early 2023, the year that went on to reach about 2 degrees by December. The same assessment offered a caution worth keeping: in 2017 the models pointed one way and the Pacific went another, developing a moderate La Niña the systems had not captured.

Why the rest of the world feels it later

El Niño is a warming of the central and eastern equatorial Pacific, but most of its consequences land far from there and well after the ocean signal appears. Events of this kind typically build through the second half of the year, peak around the turn of the calendar, and exert their strongest influence on weather elsewhere during the Northern Hemisphere winter. The lag is physical, not statistical. It takes time for the shifted band of tropical rainfall to reorganise the wider atmospheric circulation, redirecting jet streams and moisture far downstream.

So the warming building in the Pacific now points toward its broadest global effects around late 2026 and into early 2027.

What it tends to do, and what it does not promise

The teleconnections are well established as tendencies rather than guarantees. El Niño typically tilts eastern Australia, Indonesia and parts of southern Africa toward drier and warmer conditions, can weaken the Indian monsoon, and raises the risk of stressed harvests, and in the most vulnerable farming regions outright crop failures, where rainfall shifts hit agriculture hardest. It tends to bring wetter conditions to parts of the southern United States, the Horn of Africa and parts of South America. It usually suppresses the Atlantic hurricane season while energising the central and eastern Pacific.

It also nudges global mean temperature upward, which is why the 2023-24 event coincided with record global heat. Each of these is a shift in probability for a given region and season, not a forecast for any particular place. The honest position is that the Pacific is loading the dice, and the specific outcomes will depend on how the season unfolds.

What to watch

The next ENSO Diagnostic Discussion from the Climate Prediction Center is due on 11 June 2026, and it will be the first full update past the spring uncertainty window. The signals that matter over the coming weeks are concrete: whether the weekly Niño 3.4 anomaly climbs and holds above the El Niño threshold, whether subsurface warm water keeps feeding the surface, and whether the trade winds weaken and stay weak. If those line up, the case for a strong event firms. If they do not, the more moderate end of the range comes back into play.