Influence of the Agulhas Current on Summer Rainfall along the Southeast Coast of South Africa

Abstract

Summer rainfall on the southeast coast of Africa is shown to be influenced by the proximity and temperature of the adjacent warm Agulhas Current. Student's t-test correlations between coastal rainfall and local sea surface temperature (r = +0.88), shelf width (r = −0.92), and offshore distance to the thermal core (r = −0.73) all exceed significance at the 99% confidence limit. Summer rainfall patterns indicate the existence of a large-scale gradient from northeast to southwest, in the same direction as that of the SST. Alongshore variations in the rainfall gradient appear related to the distance between the coast and the warm current at the shelf edge, and to orographic effects. It is thought that a quasi-stationary mesoscale circulation system over the Agulhas Current interests with transient weather systems to produce alongshore changes in the rainfall gradient. Additionally, the modification of onshore moving air by surface heat fluxes gives rise to the close relationships between summer rainfall and oceanographic parameters along the southeastern coast of South Africa.