Moisture Source for Tropical Cyclones Genesis in the Coast of West Africa through a Lagrangian Approach

Atmospheric moisture transport plays an important role in the genesis of tropical cyclones (TCs). In this study were investigated the moisture sources associated to its genesis in the tropical Atlantic Ocean near West Africa, from 1980 to 2018 from June to November. To detect the TCs it was used the HURDAT2 database from the National Hurricane Center, and the outputs of the Lagrangian FLEXPART model were tracked to determine their moisture sources. This model permits to track backward in time the air masses from the genesis region of the TCs and to identify those regions where the moisture is uptake. The results reveal that a 18.3% (109 TC) of the total number of TCs that were formed in the North Atlantic (NATL) basin were originated in the region of study. The major frequency for the TCs genesis was observed in August and September, each one representing approximately 45% of the total. The transport of moisture for TCs mainly comes from the eastern of the North and South Atlantic Ocean, as well as from the Sahel region, providing the necessary water vapor to initiate the convective activity. A complementary analysis of atmospheric and oceanic conditions confirmed a path of moisture transport and vorticity linked to the West African Monsoon development and the African easterly jet to the Atlantic Ocean. In 1980 and 2010 were formed the major number of TCs in the study region (6 in each season). The average pattern of (E – P) > 0 for the 1980 TCs revealed an enhanced contribution of moisture from the north Atlantic Ocean from the African coast to the Iberian Peninsula. However, in 2010 was observed positive anomalies of oceanic and land evaporation near the coast of the southern West Africa, and across the Sahel, respectively. Consequently, the content of humidity raised and the wind patterns favored an interhemispheric moisture transport (south-north) along the tropical eastern Atlantic Ocean. These moisture transport mechanisms, combined with a sea surface temperature higher than 26 ºC during the NATL hurricane season leads to favorable conditions for the TC genesis.