El Niño 2026 event log: what happened, week by week
Latest entry: September 30, 2026
Short dated entries, newest first. Each one gives the number, when that number was read, and a link to the primary source it came from — a NOAA file, an official discussion, or a government page. When NOAA revises a value, the entry shows the current one and says it changed. This week's live reading is on the dashboard; the standing guide to the event is El Niño 2026.
Weekly Niño 3.4 reached +3.2 °C, the second record week in a row in a series that starts in 1981. Niño 1+2, off Peru and Ecuador, read +5.3 °C — also the highest in the series.
- Niño 3.4, weekly
- +3.2 °Cweek centred 30 Sep 2026; NOAA file read 5 Oct 2026
- Niño 1+2, weekly
- +5.3 °Cweek centred 30 Sep 2026; NOAA file read 5 Oct 2026
July–September closed with the conventional ONI at +2.16 °C, the highest for that season since the index begins in 1950 (1997: +1.79). The relative index, RONI, read +1.69 — second for the season, behind 1997 at +1.84.
- ONI, Jul–Sep
- +2.16 °CJAS 2026; NOAA file read 5 Oct 2026
- RONI, Jul–Sep
- +1.69 °CJAS 2026; NOAA file read 5 Oct 2026
Source: NOAA CPC Oceanic Niño Index (oni.ascii.txt) · NOAA CPC Relative Oceanic Niño Index (RONI.ascii.txt)
Weekly Niño 3.4 reached +3.1 °C, the highest in the series, beating +3.0 °C from the week of 18 November 2015. Niño 3 (+3.9 °C) and Niño 1+2 (+4.7 °C) set series highs the same week. The same week read +1.8 °C in 1997 and +2.0 °C in 2015.
- Niño 3.4, weekly
- +3.1 °Cweek centred 23 Sep 2026; NOAA file read 5 Oct 2026
- Niño 3, weekly
- +3.9 °Cweek centred 23 Sep 2026; NOAA file read 5 Oct 2026
- Niño 1+2, weekly
- +4.7 °Cweek centred 23 Sep 2026; NOAA file read 5 Oct 2026
California's Insurance Commissioner asked residents to review their cover before the El Niño storm season. The release notes that homeowners, renters and commercial policies typically exclude flood damage, and that flood insurance generally takes effect 30 days after purchase.
- Flood-insurance waiting period
- 30 daysCalifornia Department of Insurance release, 22 Sep 2026
“Consumers should plan rather than wait until a storm is approaching.” — California Department of Insurance
California's governor proclaimed a state of emergency for El Niño preparedness. State agencies are to stage flood-fighting supplies such as sandbags and pumps; Caltrans is to stage road-closure and snow-removal equipment. The release cites NOAA's 75% chance of a historic event.
- CPC odds of a historic Oct–Dec
- 75%CPC discussion of 10 Sep 2026, cited in the release
“We are not waiting for this season’s storms to be on our doorstep.” — Cal OES Director Caroline Thomas Jacobs
Weekly Niño 3.4 reached +3.0 °C, level with the series high from the week of 18 November 2015 — about two months earlier in the year.
- Niño 3.4, weekly
- +3.0 °Cweek centred 16 Sep 2026; NOAA file read 5 Oct 2026
NOAA's monthly ENSO discussion raised the chance that October–December exceeds every El Niño since 1950 (+2.5 °C or more on the three-month RONI) from 69% to 75%. The odds of a very strong event stayed above 90%.
- Historic Oct–Dec (RONI ≥ +2.5 °C)
- 75%CPC discussion, 10 Sep 2026
- Same, previous month
- 69%CPC discussion, 13 Aug 2026
Weekly Niño 3.4 held at +2.8 °C, level with the week before. NOAA first published this week as +2.9 °C and has since revised it to +2.8 °C; the current value is the one shown. Before 2026 no September week in the series had passed +2.1 °C (1997).
- Niño 3.4, weekly
- +2.8 °Cweek centred 9 Sep 2026, revised from +2.9; NOAA file read 5 Oct 2026
June–August closed with the conventional ONI at +1.80 °C, the highest for that season since 1950 (1997: +1.48). RONI, which nets out the warming of the wider tropics, read +1.36 — second for the season, behind 1997 at +1.50.
- ONI, Jun–Aug
- +1.80 °CJJA 2026; NOAA file read 5 Oct 2026
- RONI, Jun–Aug
- +1.36 °CJJA 2026; NOAA file read 5 Oct 2026
Source: NOAA CPC Oceanic Niño Index (oni.ascii.txt) · NOAA CPC Relative Oceanic Niño Index (RONI.ascii.txt)
Weekly Niño 3.4 read +2.6 °C for a third week running (weeks centred 12, 19 and 26 August), while Niño 1+2 climbed to +4.2 °C.
- Niño 3.4, weekly
- +2.6 °Cweek centred 26 Aug 2026; NOAA file read 5 Oct 2026
- Niño 1+2, weekly
- +4.2 °Cweek centred 26 Aug 2026; NOAA file read 5 Oct 2026
The Panama Canal Authority cut daily transit slots to 34 for bookings from 4 September and to 32 from 15 September. Its advisory puts watershed rainfall since May 34% below the historical average and inflows 44% below, and names the 2026–27 El Niño as a reason the deficit could deepen.
- Daily transit slots
- 34, then 32Advisory to Shipping A-29-2026, 20 Aug 2026
- Watershed rainfall, May–Aug
- −34%vs historical average; same advisory
NOAA's August discussion put the chance of a very strong event above 90% and gave a 69% chance that October–December would exceed every El Niño since 1950 (+2.5 °C or more on the three-month RONI).
- Very strong, fall–winter
- >90%CPC discussion, 13 Aug 2026
- Historic Oct–Dec (RONI ≥ +2.5 °C)
- 69%CPC discussion, 13 Aug 2026
“El Niño is strengthening, with a greater than 90% chance of a very strong event during the Northern Hemisphere fall and winter 2026-27.” — NOAA Climate Prediction Center
NOAA's Multivariate ENSO Index, which tracks ocean and atmosphere together, read +2.41 for June–July — higher than 1997 (+2.27), 2015 (+1.79) or 1982 (+1.65) at the same point. July–August has since come in at +2.54.
- MEI.v2, Jun–Jul
- +2.41JJ 2026; NOAA PSL file read 5 Oct 2026
- MEI.v2, Jul–Aug
- +2.54JA 2026; NOAA PSL file read 5 Oct 2026
NOAA put the chance of a very strong El Niño in October–December at 81% (June's outlook had given 63% for November–January) and the chance the event lasts through early spring 2027 at 97%.
- Very strong, Oct–Dec
- 81%CPC discussion, 9 Jul 2026
- Lasts through early spring 2027
- 97%CPC discussion, 9 Jul 2026
NOAA's Climate Prediction Center moved from El Niño Watch to El Niño Advisory: El Niño conditions were present. It gave a 63% chance of a very strong event in November–January.
- Very strong, Nov–Jan
- 63%CPC discussion, 11 Jun 2026
“El Niño conditions are present and expected to strengthen into the Northern Hemisphere winter 2026-27.” — NOAA Climate Prediction Center
Weekly values are NOAA's OISST-based Niño indices (1991–2020 base), dated by the week's centre; NOAA posts each one the following Monday. Seasonal values are dated by the season's last day. Quotations come only from official sources. New entries are added with the Friday briefing.