Rain

Rain is a transition event that can occur in any surface biome (except for the Snow Biome, where it manifests as a blizzard). When rain begins to fall the music changes and the lighting and background dims. It doesn't make water levels rise, but it does enable new and variant enemies to spawn. It's unconfirmed whether the rain event happens randomly or has a predictable pattern. During the rain, Goldfish are capable of moving on land and "walking" on their fins during rain. Also, NPCs will stay inside their homes during the rain, just like during the night.