Water leak after rainstorm - how to pinpoint?

2.5yr old home. Had a pretty strong storm pass through yesterday and our 2nd floor window at the corner of the house started dripping water. I’ve traced it up the wall/ceiling. We’ve had previous storms and didn’t have any leaks prior.

How do I go about diagnosing the source of this and what type of contractor do I call? I’ve ruled out the window since it’s coming from above it, and I’m assuming it’s not the roof since we would’ve noticed it from other storms? Do I just find a siding contractor?

Pictures of the leak location and house as it was being built

https://imgur.com/a/5qJts76/