The official Pokémon GO website has released information concerning the arrival of Alolan forms to Pokémon GO.
Originally introduced in Pokémon Sun and Pokémon Moon, Alolan forms take on the same names as the Pokémon that they are modelled after, but they have unique quirks to differentiate them from the Kanto forms. For example, while Vulpix is usually a Fire-type Pokémon, in Alola, Vulpix is an Ice-type.
Aside from the announcement, no future announcements have been made, so it is not known how they will be added into the game. Which one are you looking forward to catching?