One of the primary causes of surface cooling in the Arabian Sea during late spring and early summer is upwelling along the Somali and Arabian coasts. Along the Somali coast, upwelling apparently occurs as rather intense mesoscale phenomena associated with variations in the Somali Current. A three-dimensional numerical model of an equatorial ocean indicates that the formation and behaviour of these upwelling areas is sensitive to the orientation of the western boundary. Analysis of the local vorticity sources and sinks in the model solution indicates that the movement of the systems along the coast is caused by an imbalance between advective effects, producing northeastward motion, vortex stretching and the beta-effect producing southwestward motion, and the curl of the wind stress which is capable of producing either. These results suggest that surface cooling may be very sensitive to wind scales of the order of the baroclinic radius of deformation of the ocean near the coast.