Crying wolf with the 2023 El Niño: a predicted event that failed to materialize and an unexpected super-event by the second half of 2024?

Abstract The El Niño–Southern Oscillation (ENSO) is a phenomenon that involves the redistribution of heat in the tropical Pacific Ocean, resulting in irregular oscillations in the sea surface temperature (SST) between warm (El Niño) and cold (La Niña) phases. While ENSO originates in the tropical Pacific, its impacts are global. In July 2023, the World Meteorological Organization, formally responsible to declare the onset of El Niño, officially announced it to the media, urging governments to prepare for potential high impacts on health, ecosystems, and economies. However, our analysis of long-term meteorological and oceanographic data updated to the end of 2023 shows that while the eastern Pacific was warmer than normal in the second half of 2023, the overall configuration of the tropical Pacific climate system did not indicate a notable El Niño event. In fact, we found that the average SST over the global tropical ocean, excluding the eastern tropical Pacific, was significantly above normal during 2023. Therefore, the excess temperature in the eastern tropical Pacific during 2023 could be attributed to the overall warmth of the global tropical ocean itself. Our findings show that the 2023-24 El Niño event, initially predicted to be at least moderate and possibly strong, turned out to be weak and, de facto, the year is closing without the primary metrics, confirming it as a weaker event than the expectations. However, based on historical records, we hypothesize that the state of the Pacific climate system at the end of 2023, following the unusual 2023-24 El Niño, may lead to the development of a strong or very strong El Niño by mid-2024.