Remember the box is 30 feet above the ground, the water has nowhere to collect so Hurricane and Brooklyn are going to be the only ones who get wet ... and the chicks will be fine, there are only three and they are all still small enough to fit under Hurricane. And both the adults appear to be good at feeding quickly in the rain so the chicks don't get wetter then they have to before they get snugged back under.
Nothing to be done but wait and watch so long as it doesn't distress you of course.
According to the Weather Network Brandon is in the midst of a light thunderstorm and the rain is suppose to end in 5 hours. Hang in Hurricane!!