tnHeb “Now Noah was.” The disjunctive clause (conjunction + subject + predicate nominative after implied “to be” verb) provides background information. The age of Noah receives prominence.
tnHeb “and the flood was water upon.” The disjunctive clause (conjunction + subject + verb) is circumstantial/temporal in relation to the preceding clause. The verb הָיָה (hayah) here carries the nuance “to come” (BDB 225s.v.הָיָה). In this context the phrase “come upon” means “to engulf.”