CPC's 5 October Deck: Niño 1+2 Hits 4.5 °C as RONI Climbs to 1.7 °C

The NOAA Climate Prediction Center kept its El Niño Advisory in force in the ENSO status update prepared on 5 October 2026, reporting that El Niño is present and strengthening, with equatorial sea surface temperatures above average across the east-central and eastern Pacific and atmospheric circulation anomalies the agency describes as consistent with El Niño.

The headline figure in the deck is the spread between the Pacific's warm east and cooler west. The CPC lists the latest weekly sea surface temperature departures as 0.1 °C in the Niño 4 region, 2.3 °C in Niño 3.4, 3.3 °C in Niño 3 and 4.5 °C in Niño 1+2 — the far eastern box closest to South America. Over the previous four weeks, the agency says, equatorial sea surface temperatures were above average east of the Date Line and below average near and west of it.

How the basin got here

The CPC traces the evolution back through the year: below-average equatorial Pacific sea surface temperatures prevailed through February 2026, above-average values appeared in the far eastern equatorial Pacific in early February, and below-average waters expanded to the Date Line during June and July 2026. Since mid-April 2026, according to the agency, above-average temperatures have increased across the east-central and eastern Pacific.

Below the surface, the 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 temperature anomalies, which increased from late May to late July 2026, have since held steady, and above-average subsurface temperatures have persisted across the east-central and eastern Pacific over the last two months. The deck notes downwelling oceanic Kelvin waves initiated in December 2025, January 2026, March 2026 and June 2026.

In the atmosphere, the CPC describes below-average outgoing longwave radiation — indicating enhanced convection and rainfall — along the equator from near the Date Line to the eastern Pacific, with suppressed convection over the Philippines, Indonesia and Papua New Guinea. Low-level 850-hPa westerly wind anomalies ran from the western to the east-central equatorial Pacific, with easterly anomalies over the eastern Pacific.

Index bookkeeping

The deck gives the most recent Relative Oceanic Niño Index value, for July–September 2026, as 1.7 °C. The CPC's table shows RONI rising from -0.4 °C in February–April 2026 to 0.0, 0.5, 1.0, 1.4 and then 1.7 °C through the July–September season. The agency calls RONI "a principal measure for monitoring, assessing, and predicting ENSO" and notes that it subtracts the tropical mean (20ºS–20ºN) sea surface temperature departures from the Niño 3.4 anomaly.

The CPC also flags a data change: as of 8 October 2026, with NCEI discontinuing ERSSTv5, RONI values have switched to ERSST.v6, while weekly monitoring continues on OISSTv2.1. Under the operational definitions reproduced in the deck, a full-fledged episode requires the ±0.5 °C threshold to be met for at least five consecutive overlapping three-month seasons.

What the forecasts say

The CPC's probabilistic outlooks, both updated 10 September 2026, put the chance of a very strong El Niño at greater than 90% from September–November through November–January 2026-27. For the October–December 2026 season, the agency assigns a 75% chance of a historic event that would exceed the strength of previous El Niño episodes dating back to 1950. El Niño is expected to persist through March–May 2027, with what the CPC calls a possible chance — 55% — of ENSO-neutral conditions in April–June 2027.

Model guidance issued the same day points the same way: the NCEP CFS.v2 ensemble mean, which is forecast output rather than observation, favors El Niño continuing through Northern Hemisphere winter 2026-27.

Over North America, the CPC notes that since mid-August below-average heights and temperatures have been present over the eastern North Pacific and Gulf of Alaska, while above-average heights and temperatures have persisted over the central contiguous United States. The agency says its seasonal outlooks combine long-term trends, soil moisture and, when appropriate, ENSO. The full update is available from the Climate Prediction Center; background on the indices is collected in our glossary.