well first off, is it still under warranty? if it is, i would call the manufacturer. DONT tell them it was outside, it may void the warranty.
otherwise, the humidity could be the reason. what is the temperature there? anything above 80-85 probably isnt good for the set. the other factor could just be dust. does the rest of the room get really dusty? you may need to take the back panel off and spray it with compressed air to clean it out.
the other problem could be a change in temperature. if its really humid during the day, then gets a little chilly at night, that could bring in moisture.
or it could just be a problem with the set unrelated to the weather. its hard to say. tvs arent really meant to be outside, but ive seen many people that have them outside with no problem