as per title

Tornado deals dmg in 2 different ways: collision and periodic dmg.
While collision dmg can be blocked, periodic dmg cannot.
Due to next delay collision damage is only applied at a maximum rate of once every 26 frames. Tornadoes also have Last Collide enabled, so each tornado normally only applies collision damage once to a single target.
A single tornado lasts for 75 frames (3 seconds) and applies periodic damage within radius (2 yds) in its first frame and every 15 frames thereafter, so each applies periodic damage 5 times before expiring.