NOAA's Climate Prediction Center says El Niño continues to strengthen. Its October outlook puts the median October–December Relative Oceanic Niño Index at +2.74°C, beyond a +2.5°C threshold associated with an exceptional event. Those figures are forecasts; the observed three-month index remains to be measured.
What is known.
The October CPC discussion reports a strengthening coupled ocean-atmosphere pattern and sea-surface anomalies above +2°C in the Niño-3.4 region. The RONI outlook describes a distribution of possible October–December outcomes, with the 25th percentile at +2.54°C.
What earlier cases show.
NOAA compares the +2.5°C three-month strength threshold with its post-1950 record. Past El Niño strength is an ocean measure, not a promise of a specific flood, drought or storm at any location.
Why it is a possibility.
Existing ocean heat and atmospheric coupling make a very strong three-month outcome plausible. A shift in winds, a cooling episode or model error could keep the observed RONI below the line.
How the 83% was assessed.
Reference point. CPC's 8 October diagnostic discussion gives an 83% chance that the October–December three-month RONI reaches at least +2.5°C. The 83% estimate adopts that official probability; it is not an independent statistical calibration.
Why it could be higher. The published median is +2.74°C and CPC reports a strengthening El Niño with coupled ocean-atmosphere indicators.
Why it could be lower. The lower tail of CPC's own distribution remains below +2.5°C, and strong-event forecasts can miss extremes.
The editorial judgment. The point estimate tracks the official forecast without claiming certainty or a direct prediction of local weather disasters.
Limits of the estimate. The decisive value is the later observed OND RONI. If NOAA revises its forecast, the original 83% stays frozen for scoring.
What could prevent it.
A shift in Pacific winds or cooling of the central-eastern ocean could bring the final October–December RONI below 2.5°C. Forecast distributions can be wrong, particularly at extremes.
How it will be assessed.
YES only if NOAA's Climate Prediction Center publishes an observed Relative Oceanic Niño Index (RONI) for October–November–December 2026 of at least +2.5°C by 15 February 2027. Use the observed OND three-month RONI value in CPC's official historical/monitoring data, not a forecast percentile, a single-month sea-surface temperature, or the traditional ONI. If the observed value is below +2.5°C, this resolves NO after the deadline.
Sources and primary records
Probabilities are provisional editorial estimates, not guarantees. Sources document the present evidence and resolution rule. Read the full disclaimer.