Westerly anomalies forced by off-equatorial warming prevent the La Niña formation in 2024

Abstract Of the five strong El Niño since 1980, only recent 2023/24 event failed to transition into La Niña, whose distinctive evolution poses a significant challenge to 2024 El Niño–Southern Oscillation (ENSO) prediction and is the core focus of this study. The primary cause of this exception is an unprecedented zonal wind stress standoff over the equatorial Pacific: persistent, La Niña-triggering eastern Pacific easterlies driven by Northern tropical Atlantic warming met robust resistance from central Pacific westerlies, which were triggered by the spring North Pacific meridional mode and sustained by Southeastern Pacific warming, establishing a formidable barrier against La Niña development. Strong central Pacific thermal damping explains this sustaining effect, as its weakened meridional sea surface temperature (SST) gradient and enhanced wind-evaporation-SST feedback, ultimately suppressing La Niña. The multiple linear regression model also confirms that the wind stress anomaly was the critical suppressing factor, revealing that future ENSO predictions should incorporate atmospheric information from off-equatorial, especially after the predictive power of oceanic warm water volume diminishes.