After becoming Primal Kyogre, a heavy rain will start to fall. The main difference between this and Drizzle is that the weather is locked into heavy rain and cannot be changed by another Pokémon's moves or Abilities. Furthermore, damage-dealing Fire-Type moves won't have any effect, and the weather condition will last as long as a Pokémon with Primordial Sea remains in battle.
Primordial Sea doesn't have an effect in the Overworld.
Pokémon With This Ability