When I was growing up everybody pronounced it WEER-WOLF.
Now everybody seems to pronounce it WHERE-WOLF. I'm assuming it's an American thing. But even films with British accents seem to say 'WHERE-WOLF, no doubt for the American market.
I find this odd, particularly given the pronunciation of mere, here, sphere, sincere, adhere, revere etc.
I guess there's also premiere and derriere, but they both come from French words where a grave accent helps the 'air' sound (première, derrière).
The best evidence for the defence is there and where. But I suspect shenanigans going on with the h in both cases, which creates the AIR sound.
If I see an American werewolf round here I'm going to give it a sincere kick in the derrière.