After extension of the definition of land breeze and introductory discussion of the problem of nocturnal thunderstorms, tables are presented for Lydda Airport, Israel, showing the diurnal variation of thunderstorms and the associated surface wind-directions. There is a notable excess of nocturnal thunderstorms with wind directions in the quadrant from which the land breeze blows. The fundamental fact is pointed out that, because of the curvature of the coast of the eastern Mediterranean (concave toward the sea), the fields of the land breezes and the diurnal winds in the friction layer constitute a convergent wind field, particularly pronounced in the winter. The type of low over the eastern Mediterranean in which land-breeze convergences make an important contribution toward the formation of nocturnal thunderstorms is discussed briefly. A diagram shows the divergent nature of the sea breezes in summer, again, first and foremost, because of the concave curvature of the coast. A number of stations, located on or near notably convex coasts of the eastern Mediterranean, are shown to have daytime maxima of thunderstorm activity. U. S. Weather Bureau data also show a diurnal variation of thunderstorms which varies fairly consistently with the curvature of the coast of the United States, notably concave sections of the coast showing either a majority of nocturnal thunderstorms or, at least, a sensibly higher percentage than at the nearest convex section of the coast.