CPC's 2 November Deck: Niño 1+2 at 4.6 °C as RONI Reaches 1.7 °C

The NOAA Climate Prediction Center left its ENSO Alert System at El Niño Advisory in its 2 November 2026 briefing deck, reporting that equatorial sea surface temperatures remain above average across the east-central and eastern Pacific and that the atmosphere over the basin is behaving in a way consistent with El Niño. In the deck's summary slide, CPC says the event continues to strengthen and that a strong-to-very strong El Niño is likely through January–March 2027, with the probability remaining greater than 83%.

What the indices show

The update lists the latest weekly departures by Niño region: 0.2 ºC in Niño 4, 2.5 ºC in Niño 3.4, 3.7 ºC in Niño 3 and 4.6 ºC in Niño 1+2 — a steep east-to-west gradient, with the far eastern region running warmest and Niño 4 barely above average. CPC notes that over the past four weeks equatorial SSTs were above average east of the Date Line and below average near and west of it. Weekly monitoring in the deck uses the OISSTv2.1 dataset.

For its episode definition, CPC uses the Relative Oceanic Niño Index (RONI), described in the deck as a principal measure for monitoring, assessing and predicting ENSO. RONI subtracts the tropical-mean (20ºS–20ºN) SST departure from the Niño 3.4 departure (5ºN–5ºS, 120º–170ºW), rescales the variance to match the original Niño 3.4 index, and applies a three-month running mean. CPC's operational thresholds are a RONI at or above +0.5 ºC for El Niño and at or below −0.5 ºC for La Niña, sustained for at least five consecutive overlapping three-month seasons to qualify as a full episode. The most recent value given is 1.7 ºC for July–September 2026. CPC also flags a dataset change: following NCEI's discontinuation of ERSSTv5 on 10 August 2026, RONI is now computed from ERSST.v6, while weekly OISSTv2.1 data are unaffected.

Ocean and atmosphere

Beneath the surface, CPC reports that upper-ocean (0–300 m) heat anomalies are above average and the thermocline slope index is below average, both signatures the agency associates with warm episodes. Positive subsurface anomalies grew from late May into late July 2026 and have since held steady; positive anomalies persist east of the Date Line while negative anomalies have strengthened to the west. The deck attributes some of this evolution to equatorial oceanic Kelvin waves, noting upwelling waves initiated in October 2025 and downwelling waves in December 2025, January 2026, March 2026 and June 2026.

In the atmosphere over the past 30 days, CPC observed below-average outgoing longwave radiation — enhanced convection — along the equator from near the Date Line to the eastern Pacific, and above-average OLR, indicating 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 over the same stretch.

Forecasts and caveats

CPC's probabilistic outlooks in the deck carry an update date of 8 October 2026. They call for El Niño to persist through March–May 2027, with chances then favouring ENSO-neutral in April–June and May–July 2027, and for a strong-to-very strong event to be most likely through January–March 2027. The official outlook also assigns high chances to what CPC calls a historic event — a three-month RONI of +2.5 ºC or more, which would exceed previous El Niño events back to 1950: 54% for September–November, 83% for October–December and 70% for November–January.

Separately, the NCEP CFS.v2 forecast issued on 2 November 2026 has its ensemble mean favouring El Niño continuing through Northern Hemisphere winter 2026-27. Those plume values are model output rather than observations.

Over North America in the last 60 days, CPC noted below-average heights and temperatures over the eastern North Pacific and the US West Coast during September and late October, with above-average heights and temperatures persisting over the central contiguous United States throughout. Its November 2026–January 2027 seasonal outlooks, the agency says, combine long-term trends, soil moisture and, where appropriate, ENSO. The full deck is available from CPC; see also our glossary for index definitions.