Typically, rain on the coast beach here blows through quickly when it does rain and I have had a number of weddings where we were able to wait 20 minutes for a clear sky. The all-day downpours do happen, but not that frequently. I think last year out of 200 + weddings there along the beach I remember only 2 or 3 that had to deal with a Plan B’s for downpours.
A Plan B along the beach is either a gazebo, a porch at a beach house, or I remember several years ago a very group was allowed to use a banquet room at the condo they were at.
When it comes to rainy weather, I am flexible and keep a close eye on the forecast, too.