In meteorology, latent heat flux is the flux of energy from the Earth's surface to the atmosphere that is associated with evaporation or transpiration of water at the surface and subsequent condensation of water vapor in the troposphere. It is an important component of Earth's surface energy budget.

The latent heat flux (LE) is the energy that is absorbed by water at the Earth’s surface during evaporation or transpiration apart from any change in temperature. It is a flux or transfer of energy because we assume the resulting water vapor is transported away from the surface by diffusion and advection in the atmosphere.

Latent heat flux (LHF), the second largest term in the flux budget (second only to surface solar radiation), is the heat used to evaporate water from the ocean surface, resulting in ocean cooling, which is then released to warm the atmosphere when the vapor condenses to form clouds (Taylor et al. 2003).