The temperature of the surface layer of ocean water must be 26.5circmathrmCleft(80circmathrmFright) or warmer, and this warm layer must be at least 50mathrm~m(150 feet) deep. As the warm, moist air rises, it expands and cools, quickly becoming saturated and releasing latent heat through the condensation of water vapour. The column of air in the core of the developing disturbance is warmed and moistened by this process.