CPC's monthly ENSO Diagnostic Discussion dropped this morning with an 81 percent chance of a "very strong" El Niño by winter. Bloomberg and Weather.com are already running with "strongest in 75 years." Here's the discussion itself, numbers first, before the headline gets ahead of the data.
Every month, CPC issues one document that resets the baseline for everything written about this event: the ENSO Diagnostic Discussion. Today's edition, issued the morning of July 9, is the reason today's post exists. It's also, for once, not just this site saying the numbers are notable. Bloomberg, Weather.com, Reuters, and other outlets began reporting on the forecast within hours of release. Here's what it actually says, separated from what the headlines are doing with it.
The synopsis is direct: "El Niño continues and will strengthen through the end of the year, with a 97% chance it will persist through early spring 2027." The latest weekly Niño 3.4 index, the benchmark region, came in at +1.2°C. The western box, Niño 4, sits at +0.5°C. The eastern box, Niño 1+2, is at +2.7°C, the steepest of the three and a trend this site flagged back in June when it was "only" +2.4°C.
Underneath the surface numbers, CPC pointed to a recent downwelling Kelvin wave that deepened the thermocline and raised subsurface temperatures in the eastern Pacific, the same mechanism covered here on July 1. Low-level westerly wind anomalies and upper-level easterly anomalies were observed over the western and central equatorial Pacific. Convection was enhanced over the central and east-central Pacific and suppressed over Indonesia, the classic atmospheric signature of a coupled event. Both the traditional and equatorial Southern Oscillation Index readings were significantly negative, consistent with everything above.
CPC's own language: an 81 percent chance of a very strong El Niño during October through December that "would rank among the largest El Niño events in the historical record going back to 1950." That's the number Bloomberg's "strongest in 75 years" framing is drawing on, and it's a fair read of the data. It is not, however, a certainty, and it's not a claim that this will be the single strongest event on record. It's CPC's official probabilistic forecast, informed by the North American Multi-Model Ensemble (including NCEP's CFSv2), current observations, reanalysis, and forecaster assessment, not simply an automated model count. The remaining 19 percent breaks down further: a 16 percent chance of a strong event and a 3 percent chance of a moderate event.
The most interesting number on the page isn't the headline one. It's Niño 1+2, the eastern-most, coastal-adjacent box, now at +2.7°C against a Niño 3.4 reading of +1.2°C. That 1.5°C gap is wider than the 1.3°C gap flagged in June. That pronounced east-to-central gradient continues to give the event a strongly east-weighted signature. It's too early to treat the final event classification (east-based versus Modoki/central-Pacific) as settled, since that's usually judged from the broader spatial pattern over time rather than a single week's reading, but the present pattern is not behaving like a classic central-Pacific event. East-weighted events have historically carried a different regional impact profile than Modoki events, generally a stronger tilt toward the classic wet-Southeast, dry-Pacific-Northwest US winter pattern. These are probabilistic historical tendencies, not deterministic forecasts for any individual winter.
The persistence number matters as much as the strength number for anyone planning around this winter. A 97 percent probability indicates exceptionally high forecast confidence for the event lasting through early spring 2027, though it remains formally probabilistic rather than guaranteed. Combined with the strength outlook, the practical read is: expect this to be a full-season event, not a fast-fading one, and expect it to matter for winter outlooks issued through at least February or March.
The honest summary: NOAA's own numbers support the attention this update is getting. An 81 percent chance of ranking among the largest events since 1950, backed by a 97 percent chance of lasting into next spring, is a genuinely notable monthly release. What it isn't is a finished story. The headlines are reporting a probability as if it's already a superlative. The discussion itself is more careful than that, and so is this post.