The wind speed will often decrease at night leading to clean, groomed waves. This is great for surfing but has its own set of dangers as opposed to surfing during the day.
Why this happens is quite complex and all rests on how much the ground heats up during the day.
Why are waves better at night?
During the start of the day, the rising sun begins to heat the ground. This in turn warms up the layer of air directly above the ground up to approximately 100m or 328ft, this is called the surface layer.
As the temperature of the surface area rises it becomes more buoyant causing it to rise as a thermal plume to a height of between 1-1.5km or 3000-4800ft.
As the warmer air rises, the cooler air falls from several thousands of km above, where winds speeds are much higher due to the lack of frictional drag caused by landmasses. This effect means that as the cooler air falls the wind arrives alongside, continuing as the ground temperature continues to rise.
For surfers, this can often mean an onshore breeze ruffling the top of waves. Many surf spots are best surfed in the morning because of the lack of wind and cool mornings.
After sunset, the ground begins to cool and the surface layer cools alongside. This slowly stops the mixing of the cooler, higher speed air from much higher in the sky.