The "maritime continent" area to the north of Australia is one of three major global centres of tropical convective activity and has a fundamental role in the general circulation of the atmosphere. Tropical convection within this region is dominated by island thunderstorm activity which is strongly diurnally modulated, is deep and is geographically fixed. The storms over Bathurst and Melville Islands (11.5°S, 131°E) are representative of island thunderstorms that occur throughout the maritime continent and are believed to be primarily a response to sea breeze convergence. In this paper, we produce an indicative climatology of the Melville and Bathurst Island sea breeze (obtained during a three week period of the 1988 transition season), and we examine the surface patterns of island-scale convergence and divergence, especially in relation to the diurnal modulation of island thunderstorm activity. These observations are placed in the context of the broadscale environment and the relevant surface energy balance and radiation regimes.