Expect that percentage to nudge into the 80% possibility of rain on Saturday, with most of the precipitation occurring at night.
As a result, I would advise that people bring rain gear. Or tents, or something.
As a side note we will have a barbeque grill at our disposal, I was thinking of having a midnight snack time so we could grill some stuff and eat something. Nothing sucks worse than hunting people on an empty stomach. And MREs...well...