Videos - Battlemage and Wildhunter

I've been wondering, how fast does the Tornado deal damage? Since monsters don't have flashing invincibility frames like characters do, they should take damage as often as the skill allows (i.e: Hurricane), correct?

It does damage roughly once per second. Hits up to 6 mobs. One thing i can't figure out though is sometimes the tornado starts up immediately, rather than 2ish seconds after casting.