Most forecasts will indicate the possibilities of showers everyday, because there is the threat of showers everyday, but the showers pass quickly, and are as comfortable to be in as taking a nice shower at home on a Sunday afternoon.
I don't know where you are from, although I imagine you live in Phiily. I can guarantee you the weather will be 100% better in Las Terrenas than it is, or will be, in Philly.
