Abstract
From February to March 2024, the equatorial Atlantic experienced its highest sea surface temperatures in at least 40 years. This extreme warm event was triggered by a favorable combination of El-Ni & ntilde;o-induced westerly wind anomalies in the western equatorial Atlantic and Rossby wave reflection at the western boundary, leading to an exceptionally strong downwelling Kelvin wave. The warm event was extinguished abruptly around May by a locally-forced upwelling Kelvin wave, causing an unprecedented rapid transition to a cold phase which lasted until August. The cold event did not fully develop into an Atlantic Ni & ntilde;a due to weak Bjerknes feedback, warming from surface heat fluxes, and thermocline deepening due to a series of equatorial wave reflections. Nevertheless, the cold event is consistent with a northward shift of the intertropical convergence zone, increased rainfall over West Africa, Sahel, and Sahara, reduced rainfall over the Gulf of Guinea, and an earlier onset of the West African monsoon.
