It has been well established that tropical cyclone intensity depends crucially on sea-air heat transfer in the core of the storm, yet very little is known about the physics of air-sea interaction at the extraordinary wind speeds found in tropical cyclones. Several recent publications contain speculations to the effect that sea spray can reduce tropical cyclone intensity by cooling the surface layer. We show that, to the contrary, sea-air enthalpy flux (sensible plus latent heat flux) is enhanced by the presence of spray droplets that re-enter the ocean. Droplets that completely evaporate do not directly affect the enthalpy flux, since the heat of vaporization is then supplied entirely by the air. But droplets that re-enter the ocean at temperatures less than the ocean temperature cool the ocean and thus represent a net enthalpy flux to the atmosphere. Most droplets will be colder than the ocean, owing to partial evaporation. We will present quantitative estimates of this effect, including its dependence on wind speed, and also show the results of numerical simulations of tropical cyclones that include the effect of re-entrant sea spray.