Here's another take on this issue: does your oil light come on strong, or is it kind of dim? Sometimes if the oil pressure sensor on the top of the engine block behind the alternator gets wet or had accumulated coolant residue, on humid days the oil light will come on (it's an LED and doesn't take much current to do so). When the engine gets warm and the moisture evaporates, then the light goes off (my car does this after I had an upper radiator hose break).