Is the abnormal rain only in Tokyo? Is it all over Japan? World wide? Does it follow Hina?
I don't think it's world wide, or the consequences would have been much greater. On the other hand we see sea level rising a lot, flooding Tokyo. Shouldn't water just "flow" and rise almost evenly everywhere? Does it imply that everywhere in the world the seas have risen?
The movie does not address much directly outside Tokyo. But the novelization gives a bit more context.
It's mentioned that undoing her sacrifice means the rain resumes, flooding Japan for years to come. By the time Hodaka returns in 2024 to see Hina, most of Tokyo has been one third submerged, affecting the shape of the Kanto Plain.
This implies that the primary impact was on Tokyo and the Kanto region.
