@James
"Well is that because Maui is an island in the middle of the Pacific?"
Maui is situated in the trade wind belt and the easterly trades are as good as wind gets.
You hit on the answer, it is vertical atmospheric stability and temperature gradients.
When the sun goes down and the land temp follows, the lack of vertical temperature gradient keeps the strong higher altitude winds from penetrating to the surface.
It is still blowing at 500 m but at sea level it is calm.
As a windsurfer, knowing about wind is like a powder hound knowing about snow.
It can get very frustrating when the kite guys are ripping with their kites in a good breeze while the windsurfers are schlogging without much.
In south Texas in the spring you can almost set your watch by when the vertical mixing starts and you can sail.
As the land heats up, mixing starts around noon and the wind can go from 5mph to 20mph in a half hour.
Now that I have aged out of my favorite sport I'm getting used to it but I sure do miss it.
Maui No Ka Oi!