Climate models from the United States and Europe now agree, in their early-September updates, that this year's El Niño will peak between November and December, with sea surface temperatures around +4°C above average in the Niño 3.4 region of the central equatorial Pacific. The reading comes from Brazil's MetSul Meteorologia, published on Thursday (10). On the same day, NOAA, the U.S. ocean and atmosphere agency, raised to 97% the probability that the phenomenon will reach the very strong category by late September, up from 93% in last month's outlook, according to Folha de S.Paulo.
NOAA's latest weekly bulletin puts the anomaly at +2.7°C in the Niño 3.4 region on the ONI index, the official measure used to define El Niño. Readings at or above +2°C mean a very strong event, informally known as a Super El Niño. This year NOAA also began publishing a second index, RONI, which subtracts the long-term warming of tropical oceans; on that measure the anomaly is +1.8°C, still in the strong category. The phenomenon began in June, as equatorial Pacific waters near the coast of Peru warmed above average.
A September with no precedent in the Pacific
By historical standards, no September has ever found the Pacific this warm. In the first week of the month, the anomaly stood at 1.6°C in 2023, 1.7°C in 2015, 2.1°C in 1997 and 0.6°C in 1982, according to a MetSul survey of NOAA data. The highest weekly value ever measured in an El Niño was 3.0°C, in the week of November 18, 2015, followed by 2.6°C in the week of December 29, 1982. In 2026 the +2°C mark was crossed in the week of July 8. In 1982 that only happened on November 24, in 1997 on September 3 and in 2015 on September 16.
The speed of the buildup is what most impresses meteorologists tracking the event, according to Luiz F. Nachtigall, the MetSul meteorologist who wrote the analysis. If the peak near +4°C is confirmed, this episode would far exceed the peaks of every 20th-century event and move into territory never observed in 170 years of measurements.
NOAA's probabilities and caveats
NOAA puts at 93% the probability that equatorial Pacific temperatures stay at the very high level through January. For the October-to-December quarter it assigns a 75% chance of a historic event, more intense than every El Niño recorded since 1950.
"In the October to December 2026 quarter, there is a 75% probability of a historic event that would exceed the intensity of all previous El Niño events recorded since 1950."
The agency's statement expects El Niño to keep strengthening through the end of the year, with one caveat: an event of this magnitude raises the probability of typical El Niño impacts but does not guarantee consequences worse than normal. The effects are already visible. Indonesia is in extreme drought that feeds forest fires and blankets the country in smoke; in Palembang, in South Sumatra province, firefighters were battling fire fronts this week. Monitoring continues, with monthly model updates and NOAA's weekly bulletins on Pacific temperatures.