When you control the propaganda that lies between the data and the public, the underlying availability of the data is irrelevant. The propaganda already overwrites the data.

Honestly I would suspect that limiting the data is a strategic asset. The US can use its knowledge of weather events as leverage to cow other countries, or a weapon against countries it dislikes.

"Hello <other_country>, are you worried about the impact of weather on your population? Lower your tariff rate on us and we will be glad to help give you advanced warnings so you evacuate your people"

And likewise they would completely withhold such data from "enemy" countries.