The National Oceanic and Atmospheric Administration says the El Niño now developing in the tropical Pacific is likely to become very strong during the Northern Hemisphere fall and winter, raising the odds of weather patterns associated with major El Niño events across parts of the world.
In its Sept. 10 ENSO Diagnostic Discussion, NOAA’s Climate Prediction Center put the chance of a very strong event at more than 90% for fall and winter 2026-27. It also projected a 75% chance that the October-to-December period will reach a three-month Relative Oceanic Niño Index, or RONI, of at least 2.5 degrees Celsius — a level NOAA describes as exceeding the strength of previous El Niño events in its record beginning in 1950.
The forecast is consequential because El Niño can alter the likelihood of seasonal heat, rain, drought, wildfire conditions and storm activity. But NOAA’s assessment is a forecast of the Pacific climate pattern’s strength, not a declaration that any particular flood, drought or hurricane outcome will occur in a particular place. Regional seasonal outlooks and local weather agencies are needed to assess those risks.
What NOAA is forecasting
An El Niño Advisory remains in effect, NOAA said. The agency reported that the coupled ocean-atmosphere system showed a strengthening El Niño, with above-average sea-surface temperatures spanning much of the equatorial Pacific and atmospheric conditions responding to that ocean warming.
For August, NOAA measured a Niño-3.4 sea-surface-temperature anomaly of 1.8 degrees Celsius above average. The Niño-3 and Niño-1+2 regions registered anomalies of 2.5 degrees and 3.4 degrees, respectively. Those regions cover different portions of the tropical Pacific, so their readings need not move in lockstep.
NOAA’s official strength-probability table shows a 98% chance that the three-month RONI will be at least 2.0 degrees Celsius in October through December, and a 93% chance for November through January. The higher 2.5-degree threshold carries a 75% probability in October through December. NOAA projects a very high likelihood of a very strong event, while the prospect of surpassing every prior event since 1950 remains likely but not certain.
The agency’s formal category is “very strong.” “Super El Niño,” used in some news coverage, is not an official NOAA classification. CNN reported on Sept. 14 that a later weekly RONI reading had reached 2.0 degrees above average and used the informal “super” label in describing the event.
Why the measurements are not interchangeable
The 1.8-degree August figure in NOAA’s discussion and the 2.0-degree weekly figure reported by CNN should not be treated as competing readings of the same measurement. The former is a monthly sea-surface-temperature anomaly for the Niño-3.4 region. The latter is a weekly RONI estimate. They use different indices, different averaging periods and observations taken at different times.
NOAA’s historic-strength forecast is specifically based on a three-month RONI average. A short-lived weekly value can signal rapid development without establishing where a season-long average will end up. The Climate Prediction Center’s RONI outlook draws on multiple climate models as well as observations, reanalysis data, in-situ measurements and satellite information.
Forecasts of ENSO — the El Niño-Southern Oscillation system — are probabilistic. NOAA’s 75% estimate means the projected historic threshold is more likely than not, not that a record has already been established.
Strength can shift weather odds, not dictate local outcomes
El Niño begins with unusually warm water in the central and eastern equatorial Pacific, but its effects extend through changes in atmospheric circulation. Those remote connections, known as teleconnections, can influence the odds of seasonal weather patterns far from the Pacific.
A stronger event often gives forecasters greater confidence in some broad, recurring ENSO-related patterns. It does not mean every expected pattern will emerge, nor does it establish that the event caused a specific weather disaster. Other climate patterns, day-to-day weather variability and human-driven warming can all shape conditions in a region.
That is especially relevant for public-health and emergency planning. Heat, wildfire smoke, flooding and disruptions to food or water systems can carry health consequences, but this ENSO forecast alone cannot determine where or whether those hazards will materialize. The useful next layer of information is the location-specific probability in seasonal temperature and precipitation outlooks, followed by local forecasts as the season approaches.
NOAA’s next ENSO update will indicate whether the October-to-December three-month RONI is tracking toward the 2.5-degree threshold used in its historic-strength projection.