Formal:
* E komo mai hou (literally "Come in again") - This is a very common and respectful way to welcome someone back.
* E hoʻokipa hou ʻia ʻoe (literally "You are welcomed again") - This is a more formal and poetic way to say it.
Informal:
* Aloha hou (literally "New hello") - This is a friendly and casual way to say "Welcome back."
* Ua hoʻi mai ʻoe (literally "You have returned") - This is a simple and straightforward way to say it.
You could also use a phrase like "Ua hauʻoli au e ʻike hou iā ʻoe" (I'm happy to see you again), which is a bit more personal and expresses your joy at seeing the person.
Ultimately, the best way to say "Welcome back" in Hawaiian depends on your relationship with the person and the situation.