CPC's 9 November Deck: Niño 1+2 at 4.7 °C as RONI Climbs to 2.0 °C

The NOAA Climate Prediction Center kept its ENSO Alert System Status at El Niño Advisory in the agency's 9 November 2026 ENSO update, reporting that El Niño is present, that equatorial sea surface temperatures are above average across the east-central and eastern Pacific, and that the event continues to strengthen. CPC states that a strong-to-very strong El Niño remains likely through January–March 2027, with the probability holding at greater than 83%.

What the indices show

The deck lists the latest weekly sea surface temperature departures for the four Niño monitoring regions: 4.7 ºC in Niño 1+2 off the South American coast, 3.5 ºC in Niño 3, 2.3 ºC in Niño 3.4 and 0.2 ºC in Niño 4, the westernmost region. CPC notes that its weekly monitoring uses the OISSTv2.1 dataset, while the Relative Oceanic Niño Index is computed from the Extended Reconstructed SST analysis, which switched from version 5 to version 6 on 10 August 2026 after NCEI discontinued the earlier version.

The RONI, which CPC describes as a principal measure for monitoring, assessing and predicting ENSO, subtracts the tropical-mean (20ºS–20ºN) SST departure from the Niño 3.4 departure and applies a three-month running mean. Its most recent value, for August–October 2026, is 2.0 ºC. The agency's published table traces the 2026 climb from −0.9 ºC in December–February through 0.0 ºC in March–May, 0.5 ºC in April–June, 1.0 ºC in May–July, 1.4 ºC in June–August and 1.7 ºC in July–September. Under NOAA's operational definition, El Niño is characterised by a RONI at or above +0.5 ºC, and a full-fledged episode requires that threshold to be met across at least five consecutive overlapping three-month seasons.

Ocean interior and atmospheric signals

CPC reports that above-average subsurface temperatures have persisted over the past two months across the east-central and eastern Pacific, while below-average subsurface temperatures have strengthened in the western Pacific and spread eastward at depth. Positive upper-ocean (0–300 m) anomalies persisted from August through mid-October 2026 and have decreased slightly since, according to the deck, which also notes that recent upper-ocean heat anomalies are above average and the thermocline slope index is below average. Downwelling oceanic Kelvin waves were initiated in December 2025, January 2026, March 2026 and June 2026.

In the atmosphere, CPC describes below-average outgoing longwave radiation — indicating enhanced convection and rainfall — along the equator from near the Date Line to the eastern Pacific over the past 30 days, with above-average OLR, or suppressed convection, over the Philippines, Indonesia and Papua New Guinea. Low-level (850-hPa) westerly wind anomalies extended from the western to the east-central equatorial Pacific, with easterly anomalies aloft at 200 hPa and an anomalous anticyclonic couplet straddling the equator over the east-central Pacific. CPC judges these circulation anomalies consistent with El Niño.

Forecasts

The probabilistic outlooks reproduced in the deck were last updated on 8 October 2026. They have El Niño expected to persist through March–May 2027, with chances favouring ENSO-neutral in April–June and May–July 2027, and a strong-to-very strong event most likely through January–March 2027. CPC also puts the chance of a historic event — a three-month RONI of +2.5 ºC or more, which would exceed the strength of every El Niño since 1950 — at 54% for September–November, 83% for October–December and 70% for November–January.

Separately, the NCEP CFS.v2 forecast issued on 9 November 2026 has its ensemble mean favouring El Niño continuing through Northern Hemisphere winter 2026-27; these are model output rather than observations. The deck also carries CPC's November 2026 – January 2027 seasonal temperature and precipitation outlooks for the United States, which the agency says combine long-term trends, soil moisture and, where appropriate, ENSO. CPC notes that its summary statements are refreshed once a month, on the second Thursday, alongside the ENSO Diagnostics Discussion.