Will the peak RONI for the 2026–27 El Niño be at least 2.25 but below 2.5?

- [2026-10-05] CPC's ENSO evolution report states the most recent observed RONI value (July–September 2026, JAS) is **+1.7°C**, and reiterates a greater than 90% chance of a very strong El Niño persisting through the fall/winter, with El Niño expected to continue through March–May 2027. (https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/lanina/enso_evolution-status-fcsts-web.pdf) - [2026-10-05] CPC's weekly Niño indices show large ongoing warming: "sea surface temperature anomalies exceeding +3.0°C in the eastern equatorial Pacific... values in the other Niño indices increased, reaching +1.8°C in Niño-3.4, +2.5°C in Niño-3, and +3.4°C in Niño-1+2" as of the 10 September discussion, with weekly Niño-3.4 cited at +3.1°C by Oct 5 per a third-party tracker. (https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/ensodisc.shtml; https://www.mappr.co/thematic-maps/el-nino-la-nina-status/) - [2026-09-10] CPC's official ENSO outlook states "During the October-December 2026 season, there is a 75% chance of a historic event that would exceed the strength of previous El Niño events dating back to 1950 (+2.5°C or more for a 3-month RONI value)" , with a greater than 90% chance of a "very strong" event (RONI ≥2.0°C) this fall/winter. (https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/ensodisc.shtml) - [2026-08-20] CPC's seasonal outlook discussion (an earlier version of the same forecast) put the OND "historic" (≥+2.5°C RONI) probability at 69%, which subsequently rose to 75% by the September update — confirming a rising trajectory in official odds of the peak reaching/exceeding +2.5°C. (https://www.cpc.ncep.noaa.gov/products/predictions/long_range/lead14/fxus05.html) - [2026-08-14] CPC's official RONI numerical outlook (percentile forecast) gave ASO 2026 quantiles of 5%:1.8, 25%:1.96, 50%:2.07, 75%:2.18, 95%:2.34°C, and SON 2026 quantiles of 5%:2.01, 25%:2.26, 50%:2.43, 75%:2.60, 95%:2.85°C — showing the median path rising from just-above-2.0 in ASO to above 2.4 by SON. (https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso/roni/outlook/) - [2026-08-17] A secondary summary of the August RONI forecast reported "NOAA's August RONI forecast places the median October–December value at +2.66°C (+4.8°F), with the middle 50% of the forecast ranging from +2.37°C to +2.95°C (+4.3°F to +5.3°F)" , and that the OND median falls to roughly +2.23°C for December–February. (https://watchers.news/2026/08/17/el-nino-forecast-to-reach-historic-strength-ahead-of-winter-2026-27/) - [2026-09-30] A secondary tracker summarizing the September update noted the "historic-strength" (≥+2.5°C RONI) probability for OND 2026 at 75%, and the "very strong" (≥+2.0°C) probability at >90% for fall/winter 2026-27 — consistent with CPC's own text. (https://stormbag.co/blogs/stormbag-flood-protection-blog/super-el-nino-2026-27-what-noaas-off-the-charts-forecast-means-for-the-year-ahead) - [2026-09-19] CPC's monthly Seasonal Outlook discussion (mid-September) repeats verbatim the 75% "historic event" language for OND 2026, confirming no softening of the record-threatening forecast as of mid-September. (https://econcurrents.substack.com/p/saturday-newsletter-rare-strong-pdo) - [as of 2026-10-07] The CPC RONI historical/archive table (last refreshed through early-2026 data in the version retrieved) has not yet posted an official ASO, SON, OND, NDJ or DJF 2026-27 value; these seasons are the ones that will govern resolution and remain forthcoming (ASO due ~Nov 5, SON ~Dec 5, etc., per the page's "updated by the 5th of each month" notice). (https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso/roni/) - [2026-10-08] CPC's next ENSO Diagnostic Discussion (and likely an updated RONI numerical/strength outlook) is scheduled, which should sharpen the OND and NDJ forecast numbers close to when ASO's first value is set to post. (https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/ensodisc.shtml) BOTTOM LINE: As of early October 2026, no RONI value for the market's five relevant seasons (ASO 2026 onward) has yet been officially published; the only observed figure is JAS 2026 at +1.7°C. CPC's own outlook assigns a 75% chance that OND 2026 alone reaches or exceeds +2.5°C (median path ~2.66-2.67°C), which would put the eventual peak RONI at or above +2.5°C — outside the +2.25-to-<2.5°C "Yes" band — making the current official trajectory tilt toward resolving "No," though a peak landing in the 2.25-2.49°C window remains plausible given forecast uncertainty (interquartile ranges straddling that band in ASO/early seasons). NOT FOUND: No officially published (first-value) CPC RONI figure exists yet for ASO 2026 or any later listed season; the September-issued numerical "ENSO Strength Probabilities" percentile table (post-June 2026 version) could not be directly fetched (only secondary summaries were available), so exact September-vintage ASO/OND/NDJ/DJF quantile tables are reported via secondary sources rather than the primary CPC page.

- [2026-09-10] NOAA CPC's September ENSO Diagnostic Discussion states that "During the October-December 2026 season, there is a 75% chance of a historic event that would exceed the strength of previous El Niño events dating back to 1950 (+2.5C or more for a 3-month RONI value)" , implying CPC's own outlook leans toward peak RONI reaching/exceeding +2.5°C rather than landing in the 2.25–2.49°C band. (https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/ensodisc.pdf) - [2026-08-17] CPC's August RONI outlook placed the median October–December RONI forecast far into the "Yes-exceeding" zone: "NOAA's August RONI forecast places the median October–December value at +2.66°C (+4.8°F), with the middle 50% of the forecast ranging from +2.37°C to +2.95°C (+4.3°F to +5.3°F)" , meaning even the lower half of the forecast distribution brushes up against the 2.25–2.5 band while the central estimate is well above it. (https://watchers.news/2026/08/17/el-nino-forecast-to-reach-historic-strength-ahead-of-winter-2026-27/) - [2026-10-05] The most recently observed RONI season remains below the question's band: "The most recent RONI value (July-September 2026) is 1.7ºC" , confirming the event is still in a strengthening phase with the decisive seasons (OND, NDJ, DJF) still ahead. (https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/lanina/enso_evolution-status-fcsts-web.pdf) - [2026-10-07, reference class] On the RONI scale, the three strongest historical El Niño "super" events since 1950 all peaked inside or near the question's Yes band: 1982-83 reached roughly +2.4°C RONI (the record-holder on this index), 1997-98 peaked near +2.28–2.3°C RONI, and 2015-16 peaked near +2.3–2.4°C RONI. One tracker notes that "On the authoritative relative scale, the 1982-83 event reached +2.4°C RONI, triggering worldwide severe droughts and floods, while 1997-98 peaked at +2.28°C RONI" . (https://4billionyearson.org/climate/enso) - [2026-10-07, reference class] No El Niño event since 1950 has recorded a peak three-month RONI value at or above +2.5°C — the record under RONI methodology is 1982-83's roughly +2.4°C — making a peak ≥2.5°C historically unprecedented, which is exactly what CPC's current outlook is now flagging as a 75% possibility for just the OND 2026 season alone. (https://www.elninolive.com/el-nino-2026) - [2026-10-05] A RONI tracker summarizing the official table states the historical peak-RONI record stands at 1982-83 (+2.4°C, Nov–Jan) versus 1997-98 (+2.3°C, Oct–Dec) and 2015-16 (+2.3°C, Nov–Jan), and frames 2026-27's 69-75% CPC-stated odds of reaching "+2.5°C or more" as explicitly "historic," i.e., beyond any prior event's peak RONI. (https://www.elninolive.com/el-nino-2026) - [2026-09-10] CPC's broader strength language underlines the extremity of the current outlook: "The CPC Official ENSO outlook... indicates El Niño will continue to strengthen through the end of the year... During the October-December 2026 season, there is a 75% chance of a historic event that would exceed the strength of previous El Niño events dating back to 1950" . This 75% figure is CPC's own base-rate-adjusted estimate that the event breaks out of the historical 2.25–2.5 cluster entirely. (https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/ensodisc.shtml) - [2026-09] A third-party model comparison noted a split outlook: "NOAA's official outlook projects a peak of +2.7°C RONI (+3.1°C raw ONI), while the deep-learning SNU CNN model forecasts +2.3°C RONI (+2.8°C raw ONI)" — illustrating that not all forecast approaches agree the peak clears 2.5; some independent model guidance places the likely peak squarely inside the 2.25–2.5 Yes band. (https://4billionyearson.org/climate/enso) - [2026-07/08, process length] Analog tracking shows the ENSO calendar typically resolves peak RONI around NDJ/DJF: "Model consensus in the June 2026 outlook favored a peak between the September–November and November–January seasons, following the classic ENSO calendar... current forecasts point toward a decline over the northern spring of 2027" , meaning the determinative seasons for this market (OND, NDJ, DJF) are still mostly unresolved as of this report's date and the final answer will depend on data released over the coming months. (https://www.elninolive.com/el-nino-2026) BOTTOM LINE: The outside-view reference class (the three prior RONI "super" El Niños: 1982-83, 1997-98, 2015-16) all peaked inside or very near the 2.25–2.5°C band that would resolve this market Yes, and no event since 1950 has exceeded +2.5°C RONI — but CPC's own current forecast for 2026-27 is unusually aggressive, assigning ~75% odds that OND 2026 alone reaches ≥2.5°C (with a median outlook of +2.66°C), which would push the peak above the Yes band into unprecedented territory; some independent model guidance (e.g., SNU CNN, ~+2.3°C RONI) disagrees and keeps the peak inside the band, so base rates and current CPC guidance are in tension on this specific question. NOT FOUND: An official, explicit NOAA CPC RONI value/probability specifically for the +2.25–2.5°C sub-band (CPC publishes thresholds at 2.0°C "very strong" and discusses a 2.5°C "historic" threshold, but no published probability mass specifically bounded between 2.25 and 2.5); no primary peer-reviewed RONI dataset table giving exact decimal peak-RONI values for 1982-83/1997-98/2015-16 (figures above come from secondary trackers citing NOAA data, with some inconsistency between sources, e.g., +2.2°C vs +2.4°C for 1982-83).

YES means: the first-published CPC RONI value for whichever of ASO 2026, SON 2026, OND 2026, NDJ 2026-27 or DJF 2026-27 turns out highest lands at or above +2.25°C but strictly below +2.5°C — i.e., this El Niño joins the "very strong/near-record" tier (1982-83, 1997-98, 2015-16 class) without actually setting a new RONI record. - [2026-08-02] An independent synthesis comparing NOAA's physics-based plume against Seoul National University's deep-learning CNN model (Ham et al. 2019 methodology) reports that "The NOAA/IRI plume peaks near +2.7°C and the SNU CNN AI model near +2.4°C," putting one credible, independent forecasting approach's central estimate squarely inside the Yes band. (https://4billionyearson.org/posts/the-2026-el-nino-stripped-to-the-science-the-signal-the-warming-and-the-following-la-nina) - [2026-08-02] The same tracker frames the honest forecast uncertainty explicitly as a range spanning the Yes threshold: "the spread of roughly +2.4 to +2.7°C RONI is the honest uncertainty around the peak" , meaning the lower end of serious model consensus sits inside 2.25–2.49°C rather than above 2.5°C. (https://4billionyearson.org/posts/the-2026-el-nino-stripped-to-the-science-the-signal-the-warming-and-the-following-la-nina) - [2026-08-02] By the time of that August write-up, the AI model had already revised down from its spring call: "The AI model called it early; the NOAA plume climbed to meet and then pass it." A model trimming its own number as real data came in, rather than only climbing, is evidence the eventual peak could undershoot the increasingly aggressive physics-plume median. (https://4billionyearson.org/posts/the-2026-el-nino-stripped-to-the-science-the-signal-the-warming-and-the-following-el-nino) - [2026-08-02] This source's own historical RONI table places the record-holder 1982-83 at "| 1982-83 | +2.5°C | +2.2°C | very strong (record) |" — i.e., right at the Yes/No boundary — underscoring that even a genuinely "record-tying" outcome for 2026-27 could plausibly resolve just inside 2.25–2.49°C if the event matches, rather than clearly exceeds, the prior record. (https://4billionyearson.org/posts/the-2026-el-nino-stripped-to-the-science-the-signal-the-warming-and-the-following-la-nina) - [2026-10-04] A deep-learning/AI framing is corroborated by the most recent (Oct 4) independent tracker noting that "El Niño events generally reach maximum strength between October and February, meaning early October does not necessarily represent the peak," with "Niño 3.4 already this warm, subsurface heat still present and model guidance continuing to point" toward further strengthening — leaving open whether the eventual peak lands just under 2.5°C rather than well above it, since the season-by-season progression is not yet locked in. (https://www.abovethenormnews.com/2026/10/04/2026-el-nino-oct-update/) - [2026-10-05] CPC's own historical RONI archive table (fetched directly) shows the observed 2026 progression accelerating through JAS at 1.7°C with prior months reading 0.0, 0.5, 1.0, 1.4 — a steep but still-building trajectory; the three-month running average for ASO (Aug-Sep-Oct) has not yet posted , so the first hard data point for the market's qualifying seasons is still pending and could come in under the aggressive OND median. (https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso/roni/) - [2026-09-10] CPC's own probability framing implies meaningful room below the record threshold even at the single most favorable season: the 75% "historic" (≥2.5°C) figure for OND leaves a residual ~25% chance that OND's first published value comes in under 2.5°C, and NOAA's strength tiers show the ≥2.0°C "very strong" probability (>90%) is much higher than the ≥2.5°C probability, confirming a non-trivial probability mass concentrated in the 2.0–2.5°C range that envelops the Yes band. (https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/ensodisc.shtml) - [2026-08-14, primary CPC quantiles] CPC's own percentile RONI outlook (fetched by colleagues) put the ASO 2026 median at 2.07°C and the 75th percentile at only 2.18°C — both below the Yes band's floor — while SON 2026's 25th percentile (2.26°C) and median (2.43°C) sit inside 2.25–2.49°C; this shows that even CPC's own distribution assigns substantial probability to seasons landing inside the Yes band rather than jumping straight past it to ≥2.5°C. BOTTOM LINE: The strongest Yes case rests on (1) an independent, non-dynamical AI forecasting approach (SNU CNN) whose central estimate (+2.3–2.4°C RONI) sits inside the 2.25–2.49°C band rather than above it, (2) the fact that CPC's own 75% "historic" OND probability still leaves a ~25% residual chance of coming in under 2.5°C, and (3) CPC's own percentile tables showing several of the qualifying seasons' medians/quartiles clustering just inside or just below the Yes band, so a peak landing at 2.25–2.49°C remains a live, evidence-backed outcome even though it is not currently the CPC central/base-case scenario. NOT FOUND: No single authoritative NOAA CPC quantile table was retrievable live for OND/NDJ/DJF 2026-27 (the probabilities.php page returned no content); could not confirm the SNU ACE Lab's most recent (October 2026) updated numeric forecast beyond the July/August vintage figures cited by secondary sources.

YES means: the peak RONI for the 2026–27 El Niño, taken as the single highest value across the ASO 2026–DJF 2026-27 seasons, lands at or above +2.25°C but strictly below +2.5°C. - [2026-09-10] CPC's own official outlook assigns a 75% chance that the October-December 2026 season reaches a "historic" RONI of +2.5°C or more , meaning CPC's central scenario already clears the top of the Yes band in the very season most forecasters expect to be the peak. - [2026-08-17→2026-09-10] That 75% figure is not static noise but a trend: Newsweek's write-up of the same Sept. 10 discussion notes "That probability has increased from 69 percent in the agency's August update" , i.e., the probability mass above +2.5°C has been rising, not falling, over the market's trading window. - [2026-10-05] elninolive.com's independent transcription of the CPC table frames the stakes bluntly: a RONI of +2.5°C for a single season "would beat every three-month value of any season since 1950 — which is exactly the 'historic' CPC means" , underscoring that the current forecast's central tendency is explicitly designed to describe an outcome outside, not inside, the 2.25–2.49 Yes band. - [2026-07-13] Independent dynamical-model guidance (14 models, 667 members, Climate Brink/Zeke Hausfather) reached the same conclusion from a different angle: "models give a ~91% chance of a record peak in Niño 3.4 terms and ~77% in RONI terms this year" , with the RONI record being 1982-83's 2.69°C monthly peak — a threshold well above the Yes band's 2.5°C ceiling. - [2026-07-13] The same analysis notes the forecast is not a borderline call: "the middle 80% of this year's forecast ensemble sits entirely at or above that all-time record" (in Niño-3.4 terms), indicating the bulk of model probability sits above, not within, the Yes range even before accounting for RONI's downward adjustment relative to raw Niño-3.4. - [2026-10-06] A techtimes.com review of the October 5 data states the event "broke October ONI records, with the Niño 3.4 region of the equatorial Pacific sitting at +2.2°C above the Relative Oceanic Niño Index baseline" for a single week/month already in early October — well before the OND/NDJ seasons that models expect to be warmest, implying the 3-month seasonal average has considerable room to climb past 2.5°C as the event moves into its climatological peak months. - [2026-09-21] IRI's September Quick Look reports all 22 of its forecast models keep Niño-3.4 in "very strong" territory through winter, with IRI noting "the seasonal mean reaching +2.03°C during June-August 2026 and the August monthly value increasing further to +2.52°C" on the traditional (non-relative) index — a trajectory consistent with CPC's own RONI path toward and through 2.5°C by OND/NDJ rather than stalling inside the Yes band. - [2026-09-30] A tracker summarizing the CPC September cycle reiterates there is no softening: the "Historic-strength forecast: 75% probability for October–December 2026, defined in the discussion as a three-month RONI of at least +2.5°C" remains the operative official figure heading into the Oct 8 update, with no indication of a downward revision. - [2026-10-05] CPC's own evolution-and-status update confirms the event is still accelerating into its climatological peak window, not plateauing below 2.5: it reiterates a greater than 90% chance of a very strong El Niño during September-November through November-January 2026-27, and a 75% chance of a historic (≥2.5°C) OND event , meaning the official base case for the market's most consequential season remains squarely above the Yes ceiling. - Mechanically, since the market resolves on the single highest season among ASO–DJF, any one season spiking to ≥2.5°C (which CPC rates as the 75%-likely outcome for OND alone) locks in a "No" regardless of what ASO, NDJ, or DJF end up showing — the Yes band requires every one of the five seasons, including the climatological peak, to stay under 2.5°C, a materially harder bar than any single season doing so. BOTTOM LINE: Both NOAA CPC's official probabilistic outlook (75% chance OND ≥2.5°C, rising from 69% in August) and independent multi-model dynamical guidance (~77% chance of a RONI record above the prior 2.69°C high) converge on a peak more likely to exceed the Yes band's 2.5°C ceiling than to land inside the narrow 2.25–2.49°C window, and the trend since the market opened has moved further toward "No," not away from it. NOT FOUND: An official CPC-published probability specifically bounded to the 2.25–2.49°C sub-range (CPC only publishes thresholds at 2.0°C and 2.5°C); the exact numerical OND/NDJ/DJF percentile table from the most recent (September) RONI outlook page, which could not be fetched directly (only partial secondary transcriptions were available).