Typhoon

Anyone else notice that Typhoon sometimes doesn't go off. This is extremely annoying in arenas when a warrior is about to get knocked off the middle and typhoon wont go off.

I am not silenced, I am not in a smoke cloud, and I am not otherwise CC'd in anyway.

Anyone else having this issue?
Yes, I have this issue from time to time as well. It seems Typhoon has a "multi-part" glitch of sorts.

1. If I try to cast Typhoon immediately after another spell (i.e. mashing my Typhoon button before the GCD is up) it will sometimes "cast" the spell but not have any effect. Mana will be used, the GCD will trigger and the Typhoon cooldown will trigger, but there is no damage to enemies and no knockback.

2. More frequently, I notice that the graphic for Typhoon does not appear at all. This could have something to do with my video settings, but there doesn't seem to be any pattern to it. Sometimes the graphic is invisible and the spell hits, sometimes it doesn't hit...seems to be quite random. Sometimes the graphic is visible but the spell still doesn't have any effect.

Frustratingly enough, I can't detect any sort of pattern to either of these issues. I'm sure there are occasions where I get stunned right as I set it off and the latency between my client and the server may affect the spell, but frequently I encounter these problems when I'm standing in the clear just as you mentioned. It feels like there's definitely a glitch of some sort here, but I suppose we'll just have to wait for Blizz to work out the kinks.
How long do you want to wait?
Typhoon has been broken since cata started and blizz hasn't even acknowledged the fact.

Blizzard has stated repeatedly that they don't care about balance because we are a "third spec." Typhoon will never be fixed.
My typhoon is frequently invisible as well. Sometimes it is invisible and still works, sometimes it uses the cooldown but doesn't seem to cast at all.
This has been happening sense typhoon was first implemented in the game, its sickening how it hasent been fixed yet. Id say bout 90% of the time for me, it works; but the graphic dosent show up, 5% it dosent work at all; and 5% it works like normal.