Two steady-state situations over the Gulf of Tonkin during winter were selected for a detailed study of air-sea interaction in relation to observed cloudiness. In one case southeasterly winds prevailed, and skies were nearly clear. The cloudy situation was marked by strong outflow from the continent with very low cloud bases over the whole Gulf of Tonkin. The exchange of sensible and latent heat at the air-sea interface is calculated for these two cases, and deductions are drawn concerning the difference between the states of sky utilizing these calculations in conjunction with synoptic-scale convergence and divergence patterns.