Where the Event Stands
The headline number going into September is the Oceanic Niño Index: +1.39°C for the May-June-July period, comfortably above the +0.5°C threshold that defines El Niño. NOAA declared El Niño conditions on June 11, and the Climate Prediction Center currently gives a 63% chance the event reaches Super El Niño strength (an ONI of +2.0°C or higher) by the 2026-27 winter.
What's notable is the speed. The ONI went from −0.21°C in January-March to +1.39°C in May-July — one of the sharpest La Niña-to-El Niño flips on record, and the shortest gap between a La Niña and an El Niño since 1963. The subsurface heat in the equatorial Pacific is rivaling the build-up seen before the 1997-98 Super El Niño.
What to Watch in September
Three things matter this month:
- The JJA reading. The June-July-August ONI closes out this month and will be published in NOAA's next update. It's the first window that fully captures the post-declaration strengthening — expect it to come in above the +1.39°C MJJ figure.
- The September 10 diagnostic. NOAA's Climate Prediction Center publishes its monthly ENSO diagnostic discussion on the second Thursday (September 10). That's the official update on Super El Niño probability and the winter peak forecast.
- The plume spread. Whether the IRI/CPC model ensemble keeps tightening toward a stronger peak, or starts widening, tells you how confident forecasters are in the Super El Niño scenario.
Why the 63% Number Matters
A Super El Niño isn't just a stronger version of a normal one — it's a different beast for global weather. The last three Super events (1982-83, 1997-98, 2015-16) each reshaped rainfall, drought, and hurricane patterns on a continental scale. If 2026 joins that list, the southern US and California can expect a wet winter, Australia and Indonesia a dry one, and 2027 would likely become the hottest year on record.
For the day-to-day numbers, the El Niño Tracker updates each month as NOAA publishes new ONI data, and the IRI plume guide explains how to read the model ensemble behind the forecast.
Sources: NOAA Climate Prediction Center (monthly ENSO diagnostic discussion; Oceanic Niño Index, ERSSTv5). Data retrieved September 2026. This outlook is written before the September 10 diagnostic and will be updated after it is published.