To unlock Hurricane must kill 25 enemies with the wind charm equipped. The wind charm is located in Coastal Cliffs.
You cycle through your charms by using LB and RB. Select wind.
Now kill 250 enemies with either your sword or your bow. The enemy does not have to be weak to wind, although that helps speed up the killing process.
If you are looking for a grinding spot, for wind kills the final level is as good as any.