After defeating the Tyranitar, look for the following CP values. These values are those of a Tyranitar with perfect IV's.
Tyranitar has 251 attack, 212 defense, and 200 stamina. As a Raid Boss, it has a CP of 34707.
Tyranitar is a Dark-type and a Rock-type. It has access to the following moves:
other, viable counters
Golem and Rhydon can be used as strong Ground-type attackers.
Feraligatr, Gyarados, Vaporeon, and Kingdra are the best Water-type choices. Even a Salamence with Hydro Pump can be used.
Metagross and Gardevoir can be used for strong Steel or Fairy-type damage, respectively. Be careful of Bite and Crunch!
For less-risky Fairy-types, use an Ursaring with Play Rough or a Clefable. For Gardevoir and Clefable, watch out for Iron Tail.
IMAGE CREDIT: The Pokémon Company