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Will El Niño break NOAA's all-time record? The official ONI value for Aug–Oct 2026 (record: +2.59)
2
Ṁ100Ṁ55
Nov 12
10%
Below +2.30
16%
+2.30 to +2.44
33%
+2.45 to +2.59
41%
+2.60 or higher (new record)

Question: What value will NOAA publish for the Oceanic Niño Index (ONI) for August–September–October 2026 (ASO 2026)?

The ONI is NOAA's official El Niño yardstick: the 3-month average sea-surface temperature anomaly in the Niño 3.4 region of the Pacific. The highest ONI ever recorded is +2.59 (NDJ 2015). The 1997 peak was +2.37.

Where it stands (Oct 23): JJA 2026 = +1.80, JAS 2026 = +2.16, and the weekly Niño 3.4 readings for October are running near +3.3°C, the highest in the weekly record. September's monthly Niño 3.4 temperature was an all-time high per Copernicus. So ASO could land right around the record.

Resolution source: the CPC ONI table https://www.cpc.ncep.noaa.gov/data/indices/oni.ascii.txt (the ASO 2026 row, ANOM column). Backup if that file is down: CPC's ONI page https://origin.cpc.ncep.noaa.gov/products/analysis_monitoring/ensostuff/ONI_v5.php

Rules:

  • I use the first ASO 2026 value CPC publishes (usually early November). Later revisions don't change the result.

  • Buckets are on the published two-decimal value. "2.45–2.59" includes both 2.45 and 2.59.

  • If CPC hasn't published ASO 2026 by Nov 20, 2026, I'll extend the close until it does.

I won't trade this market for its first 7 days.

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My rough numbers: Below 2.30 ~7%, 2.30–2.44 ~25%, 2.45–2.59 ~38%, new record ~30%.

How I got there: the 3-month averages imply monthly values of about +1.7 (Jul), +2.2 (Aug) and +2.55 (Sep). October's weekly readings are ~0.4°C above September's (+3.3 vs ~+3.0 in the weekly series), so October probably comes in around +2.85. Averaging Aug–Oct gives roughly +2.5, just under the 2015 record. The uncertainty is about ±0.15, so a record is very live.

Sources: ONI table https://www.cpc.ncep.noaa.gov/data/indices/oni.ascii.txt and CPC weekly index https://www.cpc.ncep.noaa.gov/data/indices/wksst9120.for

What would move me: the late-October weekly readings. If they stay at +3.3 or higher, the record bucket goes up. My monthly split is back-solved from 3-month averages, so the actual monthly ERSST values could shift this by ~0.1 either way.

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