Ocean conditions influence the economies and climate of West Africa. Based on the 30-year daily Optimum Interpolation Sea Surface Temperature (OISST) dataset during May–October, upwelling surface variability and marine heatwaves (MHWs) at the northern coast of the Gulf of Guinea are investigated. The cooling surface decreases more rapidly around Cape Palmas than around Cape Three Points and extends eastward. MHWs variability exhibits a frequent occurrence of such events since 2015 that is consistent with the observed oceanic warming and the decrease in upwelling surface. The empirical orthogonal functions performed on the annual cumulated intensity of MHWs show four variability modes that include the whole northern coast, an east–west dipole between the two capes, a contrast between the northern coast at the two capes and the meridional section east of 5° E, and a north–south opposition. These patterns show 3-year, 6-year, and 8-year trends, and are related to coastal upwelling at the northern coast of the Gulf of Guinea. Similarly, surface ocean and atmospheric conditions are modified according to MHW periods. These changes take place before, during, and after MHW events. These results could be used to understand how this change influences the marine ecosystem, the local fisheries resources, and the extreme rainfall episodes in West Africa.

This study investigates the importance of convective systems for extreme rainfall along the northern coast of the Gulf of Guinea (GG) and their relationship with atmospheric and oceanic conditions. Convective system data (MCSs), daily precipitation, sea surface temperature (SST) and moisture flux anomalies from June to September 2007–2016 are used. The results show that 2/3 of MCSs crossing Abidjan are produced in June, which is the core of the major rainy season. Likewise, 2/3 of MCSs originate from continental areas, while 1/3 come from the ocean. Oceanic MCSs are mostly initiated close to the coast, which also corresponds to the Marine Heat Waves region. Continental MCSs are mostly initiated inland. The results also highlight the moisture flux contribution of three zones which have an impact on the onset and the sustaining of MCSs: (i) the seasonal migration of the intertropical convergence zone (ITCZ), (ii) the GG across the northern coastline, and finally (iii) the continent. These contributions of moisture fluxes coincide with oceanic warming off Northeast Brazil and the northern coast of the GG both two days before and the day of extreme rainfall events. The ocean contributes to moisten the atmosphere, and therefore to supply and sustain the MCSs during their lifecycle.

This study investigates the importance of convective systems for extreme rainfall along the northern coast of the Gulf of Guinea (GG) and their relationship with atmospheric and oceanic conditions. Convective system data (MCSs), daily precipitation, sea surface temperature (SST) and moisture flux anomalies are used from June to September 2007-2016. The results show that 2/3 of MCSs crossing Abidjan are produced in June, which is the core of the major rainy season. Likewise, 2/3 of MCSs originate from continental areas, while 1/3 comes from the ocean. Oceanic MCSs are mostly initiated close to the coast, which also corresponds to the Marine Heat Waves region. Continental MCSs are mostly initiated inland. The results also highlight the moisture flux contribution of three zones which have an impact on the onset and the sustaining of MCSs: (i) the seasonal migration of ITCZ, (ii) the GG across the northern coastline, (iii) and finally the continent. These contributions of moisture fluxes coincide with oceanic warming off the Northeast Brazil and the northern coast of the GG both two days before and the day of extreme rainfall events. The ocean contributes to moisten the atmosphere, and therefore to supply and sustain the MCSs during their lifecycle.