What happens if rain It is covered?

No, not on the outside viewing platform. You arrive inside were there is a coffee shop and souvenir shop, upstairs from there is a bar / restaurant. The entrance is inside the Mall at Hudson Yards, plenty of shops and coffee shops. Views are amazing and the surrounding area below has street vendors. It's right beside the Vessel. Hope this helps

Not the outside deck you are out in the open the mall part is definitely covered

The outside viewing deck is not covered so when raining they will inform you of the instructions.