The relationship between tropical Atlantic hurricanes (Hs), atmospheric easterly waves (AEWs), and West African mesoscale convective systems (MCSs) is investigated. It points out atmospheric conditions over West Africa before hurricane formation. The analysis was performed for two periods, June–November in 2004 and 2005, during which 12 hurricanes (seven in 2004, five in 2005) were selected. Using the AEW signature in the 700？hPa vorticity, a backward trajectory was performed to the African coast, starting from the date and position of each hurricane, when and where it was catalogued as a tropical depression. At this step, using the Meteosat-7 satellite dataset, we selected all the MCSs around this time and region, and tracked them from their initiation until their dissipation. This procedure allowed us to relate each of the selected Hs with AEWs and a succession of MCSs that occurred a few times over West Africa before initiation of the hurricane. Finally, a dipole in sea surface temperature (SST) was observed with a positive SST anomaly within the region of H generation and a negative SST anomaly within the Gulf of Guinea. This SST anomaly dipole could contribute to enhance the continental convergence associated with the monsoon that impacts on the West African MCSs formation. 1. Introduction The tropical North Atlantic is a World Ocean basin where cyclonic activity is intense. It presents a substantial interannual and interdecadal variability [1], depending directly on atmospheric and oceanic conditions. The Atlantic hurricane (H) activity occurs between July and November, and major Hs form in the Main Development Region (MDR), defined as the tropical North Atlantic south of 21°N and the Caribbean Sea. This cyclonic activity mainly originates from the African atmospheric easterly waves (AEWs) that propagate from West Africa towards the tropical North Atlantic basin and the Caribbean Sea [2, 3]. These waves, which have a 3-to-4-day period [4], are responsible for about 60% of tropical storms and minor Hs, and 85% of Hs of strong intensity [5–7]. Several studies [5, 8, 9] have even suggested that some tropical cyclones occurring in the eastern Pacific develop in association with AEWs that were initially generated in Africa and then propagated across the tropical Atlantic and Central America. Upstream in their propagation across the ocean, these AEWs are themselves generally accompanied by mesoscale convective systems (MCSs), which cross the center Sahel region between 8°N–18°N and 10°W–17°E and dissipate in the tropical Atlantic Ocean towards 20°W
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