I have a 33.5 1989. Is my 33' Hunter strong enough to do a circumnavigation?
Via the major capes or high latitudes? Not a good idea. A downwind tropical tradwind run? Absolutely, provided you and the boat are properly prepared. As long as you acknowledge that you're on a light displacement sloop and not try to sail it to places or in ways that really call for a heavy displacement cutter, you'd have to have some particularly bad luck (or exhibit phenomenally bad seamanship) to not be OK.
There's a book by Liza and Andy Copeland entitled "Cruising for Cowards" that you might want to pick up. They disagree with the conventional wisdom that a fin keel spade rudder light displacement boat isn't suitable for a circumnavigation, and they write about their experiences sailing the world on Baghera, their Beneteau sloop.
You might want to plug your boat's stats into the following:
http://www.gosail.com/boatRating.html
I was surprised when it calculated that our H336's Comfort Ratio was the same as a Valiant 40, which is widely recognized as a suitable cruising boat.
Personally I think you'd have a lot more margin for error if you traded the Hunter for somthing like an older Caliber or Columbia, maybe a small Island Packet or even a Morgan (not the O/I models though). But if you really want to go with the boat you have (which is what they recommend afterall, go now with the boat you have rather than wait forever for the perfect boat), then as long as you've done your research and made the right preparations, you should be fine.
I think your biggest problem as long as you and your boat are in good shape is going to be a severe lack of storage space. There are legs on a circumnavigation that can keep you at sea for up to 30 days, and that's a lot of fuel, water, food, and other stuff to cram into a 33 foot boat.