If you step on the carpet and water comes out is a dead give away :D

Seriously though, seems like a pretty regular thing with the sunroof drains being clogged so it's a good idea to give them a quick check.

In my case the actual tubes in the A-pillars were kinked shut so the only way to fix them was to pull off the trim.

https://i.imgur.com/M9s52sb.jpg

https://i.imgur.com/WGNrKrs.jpg