If you're referring to Pelargonium geraniums (drumstick flowers, summer bedding), and not Cranesbill Geranium (hardy perennials) keep them somewhere sheltered, out of the rain - they withstand 10 degrees of frost, but will rot if they're wet at all. You can pot them up and put them in a greenhouse, even a cold one, too. And now, immediately, if they're still ok.

See Crazy Dis blog on just this subject