Changing weather (cloudy/sunny) in same scene - constant problem

I agree. Also, there are times when you get close-up shots where you can tell by the lighting that they are swimming in an indoor facility.

*shrug* that's beach life

Well at least they shot on location most of the scenes. And there was a real sea, real beach, real streets. Thats why light changed.

These days everything would be shot in front of green screen in the studio lot. With fake beach. They would just throw around sand on few feets. Then put green screen to pretend its rest of the beach.