Is my house at risk for rain damage if concrete roofing tiles are broken or missing?

I came home yesterday and it looks like something hit my roof which caused some of the concrete roof tiles to break and become displaced. Since it is the holiday weekend, we cannot contact anyone regarding this until tuesday. In the meantime, we have some rain predicted down here in Tucson. Do I need to find some way to cover the roof or is the tar paper under the tiles protection enough from the rain. Also if I need to cover the spot, what are your recommendations on how to do so?