The strongest El Niño ever measured is still intensifying.
The Niño 3.4 region of the Pacific is running +3.4 °C against normal — a reading no instrument has recorded since measurements began. That heat is rewiring the jet stream, and over the coming months it will decide which US rivers run high, which mountains miss their snow, and where the floods go.
Weekly Niño 3.4 anomaly +3.4 °C (2026-10-28, OISST, ONI convention). ONI ASO 2026: +2.5 °C; RONI ASO 2026: +2.0 °C. Niño 1+2 +5.4, Niño 3 +4.4, Niño 4 +1.4 °C. Exceeds the prior ONI-era episode peak (2015-16, 2.59 °C, NDJ 2015) by +0.8 °C on the weekly index. CPC status: El Nino Advisory (issued 8 October 2026).
● RECORD · +0.8 °C above the 2015-16 peak NOAA CPC: El Nino AdvisoryWhere we are on the ENSO scale
Think of this as a thermostat for the whole tropical Pacific. Above +0.5 is El Niño; above +2.0 is "very strong". Below −0.5 is La Niña.
Thresholds per NOAA CPC: ±0.5 weak, ±1.0 moderate, ±1.5 strong, ±2.0 very strong; an episode requires ≥ 5 overlapping seasons. ONI is baseline-sensitive (centred 30-yr climatology); RONI subtracts the 20°S–20°N tropical-mean anomaly and is preferred for inter-decadal comparison.
The race against history
Every El Niño and La Niña since 1950
75 years of ONI
NOAA CPC official outlook
| Season | Chance |
|---|---|
| September-November | 54% |
| October-December | 83% |
| November-January | 70% |
Percentages as quoted in the CPC discussion (context in the full text).
How it works: the Walker circulation
The heat under the surface
Normally trade winds pile warm water up in the west like a bathtub tilted toward Asia. In El Niño the winds falter, the tub sloshes back, and a deep blob of warm water sits off South America — the fuel that keeps the event going.
Shape follows the canonical downwelling-Kelvin-wave structure; amplitude is set from Niño 1+2 / 3 / 3.4 / 4 weekly anomalies. Replacing with GODAS/TAO pentad sections is on the roadmap.
What this means for US rivers, snow and surf
Composite signal, not a forecast for any single storm. Pair with the CPC seasonal outlooks.
Global ripple effects
| Region | Signal |
|---|
Key numbers
| Metric | Value | Source |
|---|---|---|
| Niño 3.4 weekly anomaly (2026-10-28) | +3.4 °C | CPC wksst9120 |
| Oceanic Niño Index (ASO 2026) | +2.5 °C | CPC ONI |
| Relative ONI (ASO 2026) | +2.0 °C | CPC RONI |
| Niño 1+2 / 3 / 4 weekly | +5.4 / +4.4 / +1.4 | CPC |
| Southern Oscillation Index (std., 2026-9) | -3.3 | CPC |
| Max weekly Niño 3.4 this episode | +3.4 °C | derived |
| Prior record episode (ONI peak) | 2.59 °C · 2015-16 | derived from CPC ONI |
Glossary & methods
ENSO — El Niño–Southern Oscillation, the coupled ocean–atmosphere cycle of the tropical Pacific; the largest year-to-year driver of global weather.
Niño 3.4 — the box 5°N–5°S, 170°W–120°W. Its SST anomaly is the standard ENSO index.
ONI — 3-month running mean of the Niño 3.4 anomaly against a centred 30-year climatology.
RONI — ONI minus the tropical-mean SST anomaly, isolating ENSO from global warming.
Walker circulation — the east–west overturning of air along the equator; it weakens or reverses in El Niño.
Thermocline — the boundary between warm surface and cold deep water; its east–west tilt stores the energy ENSO releases.
Analogue composite — averaging past events of similar strength to estimate typical impacts.