An air mass that is described as having warm and moist air is called maritime tropical. This occurs when heat and moisture are transferred to the overlying air from the warm waters of the ocean or seas. Maritime Tropical air mass comes from the warm waters of the tropics and the Gulf of Mexico. When warm air moves northward moist air is transported to the United States which causes the increase in precipitation. Maritime Tropical masses are often felt in the Southeast part of the United States.