This is why the NEC states that conduit, when installed outdoors, or buried underground, it is considered a wet location. Therefore the wire or cable inside the conduit has to be listed for wet locations.

It's considered a wet location because:

1. It can leak at any of the couplings.

2. It can fill with water from condensation.

Is there any way you can pull out the Cat6 and use it as a pull string to pull new (wet location rated) wire?