Why may wāw be omitted with ʿalā katifihi sayfun in context?

Wāw with Nominal Circumstantial Clauses: Omission, Inclusion and Disputed Cases

• A pronoun automatically forbids wāw
• The fronted adverbial makes the circumstantial relation intelligible
• Every nominal ḥāl must have a postponed subject
• The tanwīn on sayfun replaces wāw