As memory serves, I believe this scene was near the Act II - Act III break. Moana is returning from the underworld being led by two giant mantas to the ocean's surface. (Apparently in animated movies no one gets the bends!)
The purpose of this sequence was to reunite Moana and her father so that:
1.) they could begin the reconciliation process. (Dad's love for Moana being clearly demonstrated by his braving the open ocean, a tribal taboo, to search for his daughter.)
2.) he would be present for the Act III climax to witness Moana's heroism. Moana thereby earning her fathers respect and admiration as their future tribal leader.
When this scene was first issued to me, one of the directors emphasized the importance of atmosphere to show the looming threat of the Volcano goddess. Black waters, dark skies, driving rain, lightning, and choppy seas. Haha. No sweat!
In this first section everything is quiet and peaceful as Moana makes her way to the surface.