I have pokémon white and I beat the elite four. I have decided to hunt..

Once you start to head for the Pokemon League for the first time, the person behind the counter at the North Opelucid Gate will tell you that a thunderstorm is raging at Route 7. Go near the second house you see along Route 7 from Mistralton, and an old lady will come from the house. She'll ask you to come in, where she'll tell you about Thundurus. When you leave the house, Thundurus will confront you and then flee. It is a roaming legendary. It will be at a different part of Unova depending on the time of day. It's in the south in the morning, and in the north during the evening. The electrical boards will tell you what Route Thundurus is currently at. Just simply go in and out of a gate in the general area Thundurus is until it starts raining. Then, look for Thundurus in the grass.

If you have Pokemon black than you can't catch him you will find tornadus instead so black version: thundorus white: tornadus

Yes go to route 7 then it will start raining hard and lightning keep going forword then a lady will come out she will start telling you stuff and thats where you start your hunt. Be careful he fleds after the first attack.

Actually, Thundurus is in Pokemon White. Tornadus is in Pokemon Black.

I have a kyurem and if you want one you have to finish the game go to giant chamber you have to go to this hole and then go strait until you see a cave door you see one hope I helped