hahhahaha...dont worry my bro, basically there is no problem either with ur wiper blade, rotor or the winshield itself....i also having this kind of problem...
my father is mech, so i ask him long time ago that my wiper blade always skip whenever its rains..my father tols me the same this which is there is no problem either with ur wiper blade, rotor or the winshield itself, the thing that makes your wiper skip whenever its rain is because you apply some rain/water resistance shield on your windscreen, so when the rubber blades moves it will bergeser with the water resistan which is coated on the glass and creat friction on it ...that's y la it skip... at the moment i dun believe, but after some time i never put the water resistance coated on the screen it will never occur again...btw its not gonna harm ur blade or ur screen...
correct me if im wrong..