Initial Structure and Downstream Evolution of Caribbean Developing African Easterly Waves

While African easterly waves (AEWs) are a common precursor to tropical cyclogenesis in the Atlantic basin, the majority of AEWs weaken and fail to develop upon departing Africa. Despite this, prior research has found that AEWs that undergo genesis in the Caribbean are on average drier and weaker when first departing Africa than AEWs that develop in the open Atlantic, closer to Africa. In this study, we investigate the initial structure and evolution of Caribbean developing AEWs and how they differ from non-developing and open Atlantic developing AEWs. 

Caribbean developing AEWs and non-developing AEWs that reached the Caribbean were identified from 1996 to 2024 using the AEW tracking algorithm developed by Downs et al. (2025). Using ECMWF Reanalysis v5 (ERA5) data, we found that Caribbean developing AEWs had statistically significant low-level northerly wind anomalies and mid-level easterly wind anomalies when first departing Africa compared to non-developing cases. While open Atlantic developing AEWs have been shown to be significantly moister with stronger low- to mid-level relative vorticity and anomalously warm upper-level temperatures compared to non-developing cases, these favorable anomalies were not statistically significant in Caribbean AEWs until around 40°W. Although not initially as favorable for genesis, Caribbean developing AEWs were, on average, able to avoid the initial significant weakening observed in non-developing cases over the eastern Atlantic and were therefore better able to take advantage of a more favorable downstream environment and strengthen before eventually undergoing genesis in the Caribbean.