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Why do trade winds become more humid as they move westward across oceans?

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World map with continents shaded in colors representing climate zones, from warm reds and yellows near the equator to cool blues and whites at the poles. — Climate Even in our warming world, there will be some chilly evenings.

Trade winds become increasingly humid as they move westward across oceans because they are in constant contact with the sea surface during their journey toward the Equator.1

As these winds travel, they facilitate evaporation, a process where liquid water transitions into a gaseous state and enters the atmosphere as water vapour. This transfer of moisture is driven by the interaction between the moving air and the ocean surface; as the air flows over the water, it absorbs moisture, thereby increasing its humidity. Additionally, as the trade winds move, they typically become warmer, which further influences the exchange of energy and moisture between the ocean and the atmosphere. This continuous replenishment of humidity is a fundamental component of the water cycle and plays a significant role in shaping global climate patterns.231