The rain … The Rain! When does it ever stop? When I was a child, after a heavy rain it felt like it took hours for it to dry up outside so I could go back out and play with my friends. In Florida, after there are hurricanes, there can be so much water that it takes days to finally dry up. When there is so much water outside, driving and moving around can be rather difficult, so waiting for everything to dry up is the safest course of action you can take.
Obviously to dry up means simply to dry. A phrasal verb for you to add to your idioms! Another example of what you can learn here at EC Miami, your favorite of the US language schools!