Heroes of the Storm II: Thread. Augmented. Logical Decision

[Malistrae]

I don't believe any of the base maps are from Warcraft, they have their own backstory. Interestingly, Hearthstone has referenced Captain Blackheart (there's a Tavern Brawl named "Captain Blackheart's Treasure"), although apparently there's also a WoW NPC who's a pirate named Burgy Blackheart.

You are right, the maps, without the exception of the Eternal Conflict ones, are completely original and have no relation to Warcraft. They do have some minimal story elements, mostly through the announcers.