Wind
Shapes the wave face
Wind blowing against, with, or across the wave makes a huge visual and tactical difference. It is the variable that changes the most through the day.
Offshore wind: blows from land toward sea
Offshore wind blows from the beach out into the ocean, directly against the front of the wave. As the wave tries to break, the wind pushes back on the lip and holds the face open longer. The result is a taller, smoother, more rideable wave.
Light offshore is the condition surfers chase. Strong offshore can be too much: it sprays water into your eyes on takeoff and can push the board back up the face.
Onshore wind: blows from sea toward land
Onshore wind blows in the same direction as the wave, pushing the lip over before the wave has a chance to organise. The face gets bumpy, the wave crumbles instead of peeling, and timing your pop-up gets harder.
Light onshore is still surfable, especially for beginners working on whitewater. Strong onshore usually means staying on the beach.
Cross-shore wind: blows along the coast
Cross-shore wind runs parallel to the beach. It is not pushing the wave open or shoving it closed; it is dragging across the surface. Light cross-shore leaves a usable face with some texture. Strong cross-shore can shred the wave just like onshore.
Gusts can ruin a calm-looking day
Wind forecasts give an average, but a 25 mph gust on top of an 8 mph average will still bump up the face every few minutes. If the gust column is much higher than the average, expect the surface to be lumpier than the numbers suggest.