Storms look stunning in trailers, but mechanically they can be vague. We try to hash out which systems the trailer evidence actually supports.
What dynamic storms would mean
Visibility: reduced during bad weather. Rain: wet surfaces altering vehicle physics. Flooding: pooling water changing how you navigate. Wildlife: animals behaving differently. NPCs: population density shifting.
Rockstar did some of these in RDR2. Others would be new ground.
What we can read from the trailer
Storms that are visually convincing. Flooding that looks dynamic instead of scripted. We can't really say anything about mechanics one way or another.
Rockstar usually ships at trailer quality. If the storms play the way they look in the trailer, the system probably works.