The El Niño Briefing #14: ONI +2.46 °C, the highest August–October on record

NOAA's Oceanic Niño Index for August–October 2026 came in at +2.46 °C. No August–October in the record is close: 1997 reached +2.04 °C and 2015 +2.02 °C. The index starts in 1950, and only two three-month seasons in the whole series ran higher, both in the winter of 2015–16: +2.59 °C for November–January and +2.50 °C for December–February.

The weekly number held. Niño 3.4 read +3.4 °C for the week centred 28 October, level with the week before. Same record, not a new one.

This week in one line: ONI +2.46 °C (Aug–Oct) · RONI +1.97 (Aug–Oct) · Niño 3.4 +3.4 °C · Niño 3 +4.4 °C · Niño 1+2 +5.4 °C · Bureau of Meteorology +2.88 °C.

The relative index tells a smaller story. CPC's RONI takes out the warming of the tropical oceans as a whole. On that measure August–October reads +1.97, just under 1997's +2.07 for the same season. Very strong either way, but on RONI 1997 is still ahead.

Further east, new highs. Niño 3 rose to +4.4 °C; before this year its best week was +3.3 °C, in November 1997. Niño 1+2, off Peru and Ecuador, reached +5.4 °C, above anything in the file, including +4.5 °C in June 1983.

The Bureau, again. The Bureau of Meteorology's relative Niño 3.4 read +2.88 °C for the week ending 1 November, the highest in a series that starts in 2008. A correction: last week we quoted +2.88 °C for the week ending 25 October. The Bureau's file now gives +2.84 °C for that week.

The same week in 1997 and 2015. Niño 3.4 read +1.9 °C in the week centred 29 October 1997 and +2.5 °C in the week centred 28 October 2015.

On the ground: Peru. ENFEN, Peru's El Niño commission, kept its coastal El Niño alert on 30 October. The warming off Peru is the strongest since the event began, it says, and the coastal El Niño should stay "extraordinary", its top category, until February 2027, then ease by June. From November to January ENFEN expects above-normal rain on the north and central coast and the western highlands, with moderate to strong episodes. Rivers in the north (Tumbes, Chira, Piura, La Leche, Jequetepeque) should run high, and from December the rise spreads to Lima's Chillón, Rímac and Lurín. The south-eastern highlands and Lake Titicaca face the opposite: less rain than normal. ENFEN expects air temperatures along the whole coast to stay far above normal, with new records, and the anchoveta to stay deep, out of reach of the seabirds and sea lions that feed on them. How El Niño plays out in Peru →

Next. NOAA's weekly file updates on Monday 9 November with the week centred 4 November. CPC's next discussion is due on 12 November, and ENFEN's next communiqué on 13 November.

Live dashboard → · Live map → · Event log →

— The El Niño Briefing