The National Oceanic and Atmospheric Administration’s Climate Prediction Center says there is a greater than 90% chance that this winter’s El Niño will be very strong. Its September 10 ENSO Diagnostic Discussion, still the current one, also gives a 75% chance that the event will be historic, exceeding every El Niño back to 1950. An El Niño Advisory remains in effect.
The wording comes straight from the synopsis: “El Niño is strengthening, with a greater than 90% chance of a very strong event during the Northern Hemisphere fall and winter 2026-27.” The next scheduled update is October 8, which will show whether those odds have moved.
The September 10 discussion, number by number
The Climate Prediction Center’s discussion is a consolidated NOAA product and names no individual forecaster. It reports that sea surface temperatures in the east-central Pacific ran well above average in August, with the Niño-3.4 index at +1.8°C and the Niño-1+2 region off South America at +3.4°C. Subsurface waters carried anomalies in excess of +10°C at depth, evidence that a large volume of warm water sits beneath the surface.
The historic-event figure applies to a specific window and a specific yardstick. For October through December 2026, the discussion assigns “a 75% chance of a historic event that would exceed the strength of previous El Niño events dating back to 1950,” defined as +2.5°C or more on a three-month basis in the relative index NOAA now uses. In February the agency replaced the older, static Oceanic Niño Index with the Relative Oceanic Niño Index, or RONI, for more accurate real-time tracking of ocean temperature departures, according to NOAA’s June announcement. That change means “historic” is measured on the newer index, so comparisons with older event rankings need care.
A forecast that climbed month after month since June
The September figures are much firmer than the first calls. When NOAA’s National Weather Service declared on June 11 that El Niño had developed, the agency’s release put the probability of a very strong event, meaning surface temperatures more than 2.0°C above normal, at 63%. Ken Graham, director of the National Weather Service, cautioned then that “every El Nino is not the same,” and that each is unique in its imprint on weather. Three months later the probability of a very strong event has passed 90%.
The Climate Prediction Center’s monthly status update, dated September 21, gives the more recent weekly readings: Niño-3.4 at 2.1°C above average, Niño-3 at 3.0°C and Niño-1+2 at 3.9°C. The same document lists the RONI value for June through August at 1.4°C and expects El Niño conditions to last through March to May 2027, with a 55% probability of neutral conditions by April to June.
Outside NOAA, the picture is similar. Columbia University’s International Research Institute, in its September quick look, reports that all 22 models in its plume forecast a very strong event, defined as Niño-3.4 of +2.0°C or higher. Different institutions define strength differently, so the figures are not interchangeable with NOAA’s, but the direction agrees.
Strong El Niño impacts are tendencies, not guarantees
Two other points in the September discussion frame the forecast. First, the advisory status is unchanged: El Niño conditions are present and are expected to strengthen, so the question is no longer whether an event occurs but how large it grows. Second, the probabilities are seasonal. They describe the fall and winter of 2026-27 as a whole. The weekly figures in the status report already sit above the August monthly values quoted in the discussion, which is consistent with the strengthening it describes.
The Climate Prediction Center is careful about impacts. With an event of this magnitude, the discussion says, “the chances of experiencing impacts consistent with El Niño are larger, though not guaranteed.” The forecast is about ocean temperatures, not about any particular storm or rainfall total.
The June NOAA release listed the usual U.S. pattern for a strong event: a jet stream shifted south, more storminess and precipitation across the southern states, warmer than usual winters in the north, and drier conditions in the northern Rockies and the Ohio and Tennessee valleys. It also flagged possible high-tide flooding and harmful algal blooms along the West Coast, and stronger suppression of Atlantic hurricanes. Those are tendencies, and no two El Niño winters have matched.
The 75% chance of a historic event is the sharper claim, since it asks for a three-month value of +2.5°C or more, higher than anything in the record since 1950. The greater than 90% call for a very strong event is the more conservative one, and it is the number the October 8 update will either confirm or revise.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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