Humidity/condensation problem in Hawaii

Aloha..This is way out of my league so hope you can help me. I was a licensed roofing contractor in Calif. (long since retired). I have been told that I was the first female licensed roofing contractor in Calif. My company did shake, tile, built-up and comp roofs but never a corrugated metal roof. I also have quite a bit of experience with single ply. Some friends from Colorado invited me to stay in their cottage in Hanalei, Kauai which is where I am now. They bought this home in June. The home has a corrugated metal roof, open beam interior ceiling. The roof is definitely leaking from the ridge area, about once a day. The owners say the previous owners had the same problem and said it was due to condensation and the humidity. That may be true but roofs are not supposed to leak. It does not leak during rain storms. I suspect a proper moisture barrier was not installed but do not know what is required. Can you advise, please? I'll follow up with a local roofer. Mahalo! Linda (Carlsbad, Calif.)