The hydrological cycle plays a fundamental role in the Earth's climate system. It is the result of a continuous circulation of water on the planet through a series of interconnected reservoirs, which involves processes of evaporation, atmospheric transport of humidity, condensation, precipitation, and surface runoff. To analyze the dynamics of water vapor in the atmosphere, a diagnosis of the integrated humidity flow in the vertical can be made with information from atmospheric humidity and wind data, while the divergence of the flow, net evaporation, and precipitation contribute to explain the precipitable water in the atmosphere. Various studies show that El Niño conditions affect the interannual and interdecadal variability in rainfall in the tropical Americas, by modifying the flow of humidity towards the region, as well as the activity of easterly waves and tropical cyclones in the Atlantic. A first approximation can be made by comparing El Niño and La Niña years and their effects on the rainy season in the intra-American seas. This comparison is made from the components of the atmospheric water balance equation. A comparison is made between the summer of 1982, characterized by the presence of an El Niño event, and the summer of 2010, influenced by a La Niña event. The main finding is that during El Niño, the moisture content in the Atlantic and eastern Caribbean region is significantly lower compared to during La Niña. This decrease in humidity translates into a reduction in rainfall in the tropical Americas.