Zapdos is here for a week (8/8-15/8 HKT), and despite having higher CP than Moltres by about 1000, it is still easier to beat than Articuno, but slightly harder than Moltres.
Your best counter type of pokémon would be rock types like golem, tyranitar, ice types like junx and piloswine (in addition with ground type, which is resistent to electric attacks) & rhydon with stone edge as the charge move.
In case you do not have enough of these pokemons, dragonite would be a wild card for this legendary raid.
Talking about ice types, lapras, dewgong & cloyster are not recommended since they are also water type pokemons, which take severe damage when an electric attack launches.
Again, make sure you dodge every charge move from the legendary Pokémon or yours will be owned very quickly.