Precipitation Pattern in Cape Verde Islands: Santiago Island Case Study

Cape Verde is an archipelago composed by ten islands, located between 14°N-18°N and 22°W-28°W in the Atlantic Ocean. Previous studies associated Cape Verde's rainfall regime with ITCZ. In this study, we reviewed this hypothesis using long-term observed rainfall time series, obtained from the Cape Verde National Institute of Meteorology and Geophysics, for Santiago Island stations network, a total of 4 stations. Monthly and seasonal indices were calculated by standardizing the rainfall monthly totals in the 1981-2009 period. Time section plots of zonal and meridional wind components anomalies over the region were made using reanalysis data from ESRL/PSD/NOAA website. Daily Outgoing Longwave Radiation (OLR) time section plots were also made as proxies for weather systems propagation. Results of the analysis showed that Santiago presents a seasonal rainfall regime characterized by dry (November-June), and rainy (July-October) seasons, with a short transition period. As ancient studies, it is observable a strong relation between altitude and total precipitation amount. The weather systems within the rainy season of wet years were associated with positive anomalies of zonal and meridional wind components of relative short duration, while negative anomalies dominated in the dry years. These results suggest that west to southwesterly winds, coming from warm Atlantic Ocean associated with cold front remainings, are the rain-producing events in wet years, not the ITCZ. North to northeasterly winds, coming from the Sahel, produces dry years.