If sun stays up Metagross is a gonner i dont think dragonite is a good replacement seeing you already have a dragon on your team
id use Gastrodon hes a great counter to other weather effects
Gastrodon@Leftovers
Bold Hp 252, Def 252, Sp.Def 4
or
Calm Hp 252, Sp.Def 252, Def 4
Storm Drain
Scald...