Humidity

Humidity is the amount of water vapour in the air around a vessel, normally expressed as relative humidity: the percentage of moisture the air holds compared with the maximum it can hold at that temperature. At sea it is closely tied to evaporation, cooling air, condensation, cloud formation and the likelihood of reduced visibility or precipitation.

For boaters, humidity helps interpret changing conditions, especially during night watches, coastal approaches and offshore passages. High humidity combined with falling air Temperature can lead to Fog, making visual navigation and collision avoidance more difficult. It also increases the chance of Rain or drizzle, affects crew comfort, and can leave decks, sails and electronics damp.

Forecast models used by PredictWind factor moisture into broader marine weather guidance alongside wind, rain, cloud and Pressure. Checking humidity-related signals in forecasts helps crews anticipate visibility changes, squalls, damp gear and uncomfortable heat during coastal cruising or offshore passages.