Which air mass is usually characterized by relatively warm and moist air?

The maritime tropical air mass is characterized by relatively warm and moist air because it originates over warm ocean waters. The temperature of the air mass reflects the warmth of the water it forms over, leading to higher temperatures. Additionally, as the air moves over the ocean, it picks up moisture from the water surface, leading to the humid characteristics of this air mass. Maritime tropical air is often associated with warm, moist conditions, which can result in the formation of clouds and precipitation when it interacts with other air masses or rises over land.

In contrast, continental polar air masses are typically cold and dry, as they originate over large land areas in high latitudes. Maritime polar air masses are cool and moist but not as warm as maritime tropical. Lastly, continental tropical air masses are warm and dry because they form over land in low-latitude regions where temperatures are high. The distinction among these air masses largely comes down to their source regions and the physical conditions of those areas, making maritime tropical the clear answer when looking for a warm and moist air mass.