You can paint both the exterior and interior of your house when it rains but not with rain touching the painted surface. … For both exterior and interior surfaces, you can expect it to take longer for the paint to dry in the humid conditions of a rainy day than on dry, sunny days.
Rainy days and wet surfaces pose two major problems for painting. Rain will wash wet paint off the surface and paint won’t be absorbed into a wet surface. When it is raining outside, the paint will wash away if it isn’t dry. The best way to handle this is to be sure to avoid rainy days.