Connecting African Easterly Wave Development and Offshore Precipitation

Transition of African Easterly Waves from continental West Africa to the Atlantic Ocean leads to high variability in precipitation and difficulty forecasting in this coastal region. Meridional wind data from radiosondes launched from the island of Sal, Cabo Verde is used to connect African Easterly Wave development and precipitation near coastal West Africa. We employ two methods to examine two different aspects of this link. Firstly, we utilize the direction of meridional wind to identify the relative position of the waves to Sal. Then, we create composites of coastal precipitation during all days with northerly, southerly, and neither wind direction using satellite-derived precipitation data. Secondly, we use the meridional wind data to measure how the strength of waves affects coastal precipitation. We define two regions, one along the West African coast, and a second further southwest, towards the Intertropical Convergence Zone. These regions are used to quantify the average precipitation so a comparison can be made between both the meridional wind and precipitation totals. We find that on days with northerly winds, rainfall is enhanced to the southwest, near the Intertropical Convergence Zone. On days with southerly winds, precipitation is enhanced in the coastal region and sparse to the southwest. In terms of wave strength, we find that there is little relationship between meridional wind strength and precipitation amounts, although there is a slight tendency for more coastal precipitation when southerly winds are stronger on Sal, and more Intertropical Convergence Zone precipitation when northerly winds are stronger on Sal.