In my other game the rain starts at second day of spring, in my main i'm on summer and never rain it's so quirky. I need fishes and materials that appear when it rains
I think it might then be just random. Be patient and keep playing. If it doesn't rain until winter, then it may be a bug, I guess. Otherwise you might check a mod that changes the weather. I think the Cheat Mod can do that. Go to the Mod section and look.
Same issue. I'm on the 20th of Summer, and I've had a total of 2 rain days the entire game. My wife started playing when I did, and on her computer, she has rain every second or third day.
I got very few rains til mid summer, than it was storm every other day, sometimes even consecutive days.