Like if it's a storm the rain could actually soak you up and could get you sick if you're not wearing proper clothing to protect you. Nothing to dramatic but just something noticable like constantly coughing/sneezing that could affect gun battles.
Which would give hats and coats a purpose other than fashion statements also.
The wind could actually affect your movement and knock you down if strong enough, and if Rockstar will make objects around the city realistic we could see things like tree branches snap apart and fly all over the place. Objects that can hurt you if they fly into you so you'd have to get out of the way asap.
Hail: Chunks of ice falling from the sky that could hurt your health if you get caught in it at any time.
Getting struck by lightening being possible. I think it be hilarious to see someone else getting hit with a random lighting bolt every once in a while.
Characters sweating when it's extremely hot and possibly fainting. Especially if you're wearing waay too much stuff during a hot day.
Would any of this be welcomed by yall? I think at the least rain should get hair soaked. It doesn't even do that in the shower and it's pretty ridiculous imo.