El Niño 2026 vs. 1997-98: How the Two Events Compare, Month by Month

Two events, the same calendar position, a decade apart in everything except the numbers. This page sets 2026–27's Niño 3.4 readings directly against 1997-98 — the benchmark super El Niño — at matching points in each event's calendar, rather than comparing a mid-event reading to a final peak. For the full narrative of the 2026 event, see the event page; for 1997-98's complete story, its own history page is the deeper read, alongside the other super El Niños since 1950. The current numbers, updated as they land, are always on the live dashboard.

Same calendar stage, different pace

The table below lines up monthly Niño 3.4 anomalies for both events by calendar month within the onset year — April through July — rather than by days-since-threshold, so the comparison uses the same clock both events were tracked against in real time.

Every April-through-June figure above is a monthly average of that month's weekly Niño 3.4 readings; July 2026 is still in progress, so its entry is the single latest weekly reading rather than a monthly mean — comparing a partial month to 1997's completed July would understate how much of July remains to be counted. Even so, the late-July weekly value already sits solidly inside the "very strong" band (at least +2.0°C), a tier 1997 did not enter until autumn.

The race chart above extends the same comparison across the full event, month by month from January of the onset year through June of the following year, and adds 1982-83 and 2015-16 for context. Both this table and the chart draw on the same NOAA source series: the weekly SST file for 2026's in-progress trajectory, and the long-run monthly Niño 3.4 record for 1997-98's completed one.

Onset: how each event got here

1997's onset followed the classic pattern: a fading La Niña through early spring, a neutral ocean by April, then a fast warm-up as westerly wind bursts fired in the western Pacific and downwelling Kelvin waves carried heat east. Weekly readings crossed into El Niño territory by late spring, and the event was unmistakable by June 1997.

2026 followed a strikingly similar script. The 2025–26 La Niña unwound in February–March, April sat near neutral at the surface while a substantial warm reservoir loaded up below it, and May's Kelvin wave pulse pushed weekly readings across the +0.5°C threshold — the sequence covered as it happened on the forecast page. Both events, in other words, spent the same six-week window doing the same physical thing: converting a loaded subsurface into a surfacing warm anomaly.

The official outlook for 2026–27 today

1997 had no equivalent of a monthly probabilistic outlook in the form used today — the CPC/IRI seasonal probability format matured largely because of the lessons that event taught forecasters. 2026 does: the most recent CPC/IRI outlook puts the odds of a very strong event (at least +2.0°C at peak) at 81%, at least a strong one at 88%, and roughly 97% odds El Niño persists into early spring 2027, with the peak expected October–December 2026. Those are odds, not a promise — the full breakdown, updated after every monthly outlook, lives on the forecast page.

What's different this time

Running ahead of 1997's pace at the same calendar stage is real, but it isn't the whole story. A few differences are worth holding alongside the numbers:

• A warmer starting ocean. Global sea surface temperatures have risen measurably since 1997, so today's absolute readings sit on a warmer baseline than 1997's did — part of why some forecasters cross-check the headline Niño 3.4 anomaly against the Relative Oceanic Niño Index, which adjusts for that background warming.
• Denser observations, better models. The TAO/TRITON buoy array, satellite altimetry and today's coupled ocean-atmosphere models give forecasters a clearer, earlier read on the subsurface heat reservoir than anything available in 1997, which is part of why 2026's odds could be stated with unusual confidence this early in the season.
• A still-open outcome. 1997-98's Oceanic Niño Index peaked at +2.4°C in the November–January season — running ahead in July guarantees nothing about November. 2026's own peak is still several months out, and each monthly outlook narrows the range further.
• More exposure in the path. More people, infrastructure and capital now sit in the regions strong El Niños affect than did in 1997, which is the practical reason the comparison matters beyond scientific curiosity — see the impact guides for what strong-to-very-strong intensity has meant region by region.

Bottom line

At matching points on the calendar, 2026's Niño 3.4 readings are running warmer than 1997-98's — a monthly average of +1.58°C in June 2026 against +1.22°C for 1997, and a late-July weekly reading of +2.2°C against 1997's +1.67°C monthly figure for the same month. That pace, plus a July 2026 outlook putting 81% odds on a very strong event, is why 1997-98 is the comparison this season keeps coming back to. It is not yet a verdict: 1997-98's +2.4°C Oceanic Niño Index peak arrived in winter, and 2026's own peak — favored for October–December — hasn't happened. Track how the gap moves on the dashboard, read 1997-98's full story on its history page, and follow the odds as they update on the forecast page.