Tempest Roar is a Unique Helm in Diablo IV Season 15. It comes from World drop (any difficulty, drop rate scales with Torment tier); Horadric Cube: Item Transmutation (Upgrade to Unique) - Common item of the same slot + 1 Enhanced Primordial Dust + 10 Primordial Dust (random Unique of that slot).
Unique power
Lucky Hit: Storm Skills have up to a [15-35]% chance to grant 4 Spirit. Your base Storm Skills are now also Werewolf Skills.
Affixes
1,200 Armor
+[1-20] Maximum Resource
+[2.5-21.3]% Willpower
+[35-94] Willpower
+[1-630] Lightning Resistance
Where it drops
World drop (any difficulty, drop rate scales with Torment tier)
Horadric Cube: Item Transmutation (Upgrade to Unique) - Common item of the same slot + 1 Enhanced Primordial Dust + 10 Primordial Dust (random Unique of that slot)