The 2026-27 El Nino event, dated

This page is a living event log: it auto-appends a new line after every CPC ENSO Diagnostic Discussion cycle, so the list below grows as the season plays out. It's deliberately compact — a scannable, dated record of what's happened and what's scheduled next. For the detailed monthly write-up behind each entry — what actually changed, in plain language — see the update log. For current index readings and advisory status right now, see the live dashboard. Nothing on this page is a live number; it's a schedule and a record, not a snapshot.

Timeline

1. 2025 (approx.): ENSO-neutral conditions prevail through the year — the Nino 3.4 anomaly sits inside the roughly ±0.5°C neutral band, with no sustained El Nino or La Nina signal.
2. Spring 2026: Sea-surface temperatures begin a fast warming ramp in the central and eastern tropical Pacific, the leading edge of what would become this event.
3. June 11, 2026: NOAA issues an El Nino Advisory, upgraded from a Watch — the official signal that El Nino conditions are observed and expected to continue, not just favored to develop. See the glossary for the Watch-vs-Advisory distinction.
4. June–July 2026: Rapid strengthening continues. CPC's probability guidance for a very-strong (≥+2.0°C) event by peak season rises notably month over month, though this remains guidance about likelihood, not a locked-in outcome — see what a very-strong event would mean.
5. Ongoing — Aug 13, Sep 10, Oct 8, Nov 12, Dec 10, 2026: CPC's ENSO Diagnostic Discussion, issued on the second Thursday of each month (CPC ENSO Diagnostic Discussion). Each of these is a scheduled milestone on the calendar, not a preview of what it will say; the detailed writeup for each one lands on the update log shortly after it's issued.
6. Mid-October 2026: NOAA's headline seasonal winter outlook release — the temperature and precipitation probability maps most people are actually waiting for. This is typically the single highest-traffic day of the entire event arc, since it's the first official "what will my winter look like" product of the season. See Winter Forecast 2026-27 and the regional impacts hub once it's out.
7. Nov 2026 – Jan 2027: Expected peak strength window, per current CPC guidance. El Nino events typically peak in Northern Hemisphere winter before fading through spring; this window is where that peak is currently expected to fall, not a guaranteed date. Actual peak timing and magnitude will be confirmed only as the data comes in — check the live dashboard and the ONI/RONI index page for current readings as they update.

A note on what this page won't do: it won't retroactively fill in future dates with numbers we don't have yet. Every entry above for a date that hasn't happened is described as scheduled or expected, sourced to CPC's own published cadence and guidance — never as a specific outcome we're predicting in advance. When each date actually arrives, the real figures belong on the dashboard and the index page, and the story behind them belongs on the update log; this page just gets a new dated line pointing to both.