The water is from the outside the rain but the car has no signs of leaks are there exterior drains that could be clogged on a 1999 Porsche boxster?

There are drain holes under the roof. put the roof in the service position then check out the soft rubber trays either side of the roof and you will see the holes. gently rod them out then pour water down and it should come out under the car. if this doesn't work then check the rubber trays for signs of wear or tear as water will leak out behind the seats if this is not sorted.