Idk what happened but I can keep coming back to a specific day and Celeste + Meteor showers are occuring. I can time travel several times to other days, come back, no Isabelle intro happens and I get the same stars + Celeste. The game treats it like a different day that I just already saved on each time?????
Meteor showers are baked into certain dates upon creating your island. Not all showers are announced by Isabelle (only heavy ones, and not always). I'd say it's perfectly normal.
There's a site you can input your weather data into to find out when your next meteor showers will be, so you don't have to keep going back: https://wuffs.org/acnh/weather/
What was already said. Meteor showers are pre-determined by your weather seed, at least for now if Nintendo doesn't patch it down the road. Everything down to the exact second that the stars appear is already programmed into your game. That will never change.
Celeste is not guaranteed on a meteor shower day, but the shower itself is.
