In September, equatorial sea surface temperatures (SSTs) were above average [Fig. 1], though positive anomalies weakened in the eastern Pacific. All of the latest weekly Niño index values remained in excess of +1.0°C: Niño-4 was +1.2°C, Niño-3.4 was +1.5°C, Niño-3 was +1.9°C, and Niño1+2 was +2.6°C [Fig. 2]. Area-averaged subsurface temperatures anomalies decreased [Fig. 3], but remained above-average, consistent with elevated subsurface temperatures across the central and eastern equatorial Pacific Ocean [Fig. 4]. Tropical atmospheric anomalies were consistent with El Niño. In areas of the central Pacific, low-level winds were anomalously westerly, while upper-level winds were anomalously easterly. Convection was enhanced around the International Date Line, stretching into the eastern Pacific, just north of the equator. Convection was suppressed near Indonesia [Fig. 5]. The equatorial Southern Oscillation Index (SOI) and the traditional station-based SOI were both significantly negative. Collectively, the coupled ocean-atmosphere system reflected El Niño.

The most recent IRI plume favors El Niño to continue through the Northern Hemisphere spring 2024 [Fig. 6]. Also considering recent observations and the NMME, the team favors at least a "strong" event with a 75-85% chance through November-January (≥ 1.5°C for the seasonal average in Niño-3.4). There is a 3 in 10 chance of a "historically strong" event that rivals 2015-16 and 1997-98 (seasonal average ≥ 2.0°C). Stronger El Niño events increase the likelihood of El Niño-related climate anomalies, but do not necessarily equate to strong impacts locally. Consider consulting CPC seasonal outlooks for probabilities of temperature and precipitation in the coming seasons. In summary, El Niño is anticipated to continue through the Northern Hemisphere spring (with an 80% chance during March-May 2024; [Fig. 7]).

This discussion is a consolidated effort of the National Oceanic and Atmospheric Administration (NOAA), NOAA's National Weather Service, and their funded institutions. Oceanic and atmospheric conditions are updated weekly on the Climate Prediction Center web site (El Niño/La Niña Current Conditions and Expert Discussions). Additional perspectives and analysis are also available in an ENSO blog. A probabilistic strength forecast is available here. The next ENSO Diagnostics Discussion is scheduled for 9 November 2023.

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