Looks like this will be too late for this particular trip, but there is a nice anchorage on the western tip of Vieques. It's not an ensenada (harbor), just a nice anchorage location sheltered from the typical E or NE winds. It's called Punta Arena, and many of the locals call it Green Beach. Just look for the western tip of Vieques and anchor
on the west side. We used to anchor there a lot and never had problems.
If you're looking for easy in and out and fast access to Puerto del Rey the next day, this is a good spot - since it's not a harbor there is no maneuvering, just find a spot and drop anchor in about 10 feet, it's mainly sand. And the trip to Puerto del Rey is easy and well marked, just head
west for the nearby buoys marking the main channel into the old Roosevelt Roads and you will avoid the sand bar that juts out from the west of Vieques, although I never had problems sailing over it. I never saw less than 8-10 feet, but you know how sand bars can shift.