Where is it raining exactly?
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.