Humidity is the presence of water vapor in the atmosphere. Due to day time heat in the sea, a lot of evaporation occurs on the surface of the water body. As humid air is heavier, it remains on the surface of the sea. During the day time, the land is warmer than the sea because of which the air is less dense in the land than at sea. Air moves from the region of higher density to a region of lower density and this causes the sea air to be blown towards the adjoining coastal regions thus bringing in a lot of water vapor and thereby increasing humidity.