Why do onshore and offshore breezes occur along the coast?

Even in the absence of major wind systems or rain showers, there will still often be a coastal breeze because sunlight heats land surfaces more rapidly than sea surfaces. During the day this generates rising air and a breeze blowing from the sea onto the shore. During the night, the land cools more rapidly so there is sinking air flowing from the shore to the sea.

Daytime winds are generally sea breezes and night winds are generally land breezes.