Columbia/IRI, along with Australia's BoM have become our go-to quick
hits for the El Niño-Southern Oscillation. For the deeper dives, we
consult the NOAA in the U.S. and Japan's "Japan Agency for Marine-Earth
Science and Technology" (JAMSTEC).
JAMSTEC defined the modoki flavor of El Niño which arises in the central
rather than the eastern Pacific with the Japanese word meaning "similar
but different", handy for dropping casually into conversation at the
Thursday afternoon salon.
First, a note on terminology for normal people who don't obsess about this stuff:
- ENSO = the El Niño/Southern Oscillation
- ENSO Neutral = the ocean surface temperature anomaly in the ENSO 3.4 region is between +0.5°C and -0.5°C.
- El Niño/La Niña conditions exist when the anomaly is greater than (Niño) or less than (Niña) the half-degree cut-off for neutral.
- A full blown El Niño/La Niña is declared when the conditions persist for three overlapping three-month periods i.e. five consecutive months.
From IRI/Columbia, September 19:
ENSO Forecast
September 2025 Quick Look
A monthly summary of the status of El Niño, La Niña, and the Southern Oscillation, or ENSO, based on the NINO3.4 index (120-170W, 5S-5N)
As of mid-September 2025, the equatorial Pacific remains in an ENSO-neutral state, with sea surface temperatures in the Niño 3.4 region close to average but exhibiting a gradual cooling trend. The IRI ENSO plume forecast indicates a moderate probability (56%) of La Niña conditions developing during September–November 2025. These La Niña conditions are expected to persist through the boreal winter of 2025/2026 (December–February). However, beginning in January–March, ENSO-neutral conditions are forecasted to return, with probabilities ranging from 55% to 74%, while the likelihood of La Niña gradually decreases. The chances of El Niño development remain very low—below 10%—through March–May 2026....
....MUCH MORE
And the plume of the various dynamic (DYN) and static (STAT) model predictions:
The thicker lines are the averages of the two types of models and the consolidated model forecast from NOAA's Climate Prediction Center.
For a deeper dive, IRI/Columbia also features the CPC ENSO Update.
