For it (actor) to make daylight conditions (patient -on) dull.
Actor, presumably clouds, occurs only in the sentence as a pronoun -na `it'. A substantive with patient role, presumably daylight conditions, is unexpressed in the sentence.
Lidudumōna hi munggāwa ti den do'ol di būnut.
It will make (it) dull in the late morning because, you see, there are many clouds.