What causes onshore breeze and fog?

Onshore breezes and fog are primarily caused by the differential heating of land and water. When the sun heats the land during the day, it warms up faster than the ocean. As the land temperature rises, the air above it also warms and becomes less dense. This warm air rises, creating an area of lower pressure over the land.

Meanwhile, the ocean remains cooler due to its higher specific heat capacity, which means it absorbs and retains heat differently than land does. The relatively cooler air over the ocean remains denser and creates higher pressure. The difference in pressure leads to a onshore breeze, as air moves from the high-pressure area over the ocean to the low-pressure area over the land.

Furthermore, when moisture-laden air moves in from the ocean and encounters cooler air near the surface, especially in the presence of a cool breeze, it can condense to form fog. The combination of these factors ultimately results in the characteristic onshore breeze and fog typically observed in coastal regions.