ONI (Oceanic Niño Index)
Updated: July 2, 2026 · 1 min read · Live dashboard
The Oceanic Niño Index is the number that makes El Niño official. NOAA computes it as a three-month running mean of the sea-surface-temperature anomaly in the Niño 3.4 region, using the ERSSTv5 dataset against a rolling 30-year climatology. Each value carries a season label — "NDJ" is November–December–January — and the full table back to 1950 is the reference history of every El Niño and La Niña on record.
The thresholds are simple: +0.5°C or above is El Niño territory, −0.5°C or below is La Niña. For an official event classification, NOAA requires five consecutive overlapping seasons beyond the threshold. Intensity is graded by the peak value: weak (0.5–0.9), moderate (1.0–1.4), strong (1.5–1.9) and very strong (2.0 and above) — the tier often called a "super El Niño." The record peaks: +2.2°C in 1982-83, +2.4°C in 1997-98 and +2.6°C in 2015-16.
Because it smooths across three months, the ONI moves deliberately — the weekly readings on our dashboard lead it, and the seasonal index confirms. The 2026–27 event's climb through the table is exactly what the ONI history chart on this site tracks.
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Keep reading
Niño 3.4
The equatorial Pacific box (5°N–5°S, 170°W–120°W) whose sea-surface-temperature anomaly is the standard measure of El Niño's strength.
RONI (Relative Oceanic Niño Index)
The ONI recomputed relative to average tropical ocean warming — a fairer gauge of El Niño's true atmospheric punch in a warming world.
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