It will be raging from the Northeast 15 to 20 mph, 5 of 7 days. You'll get the Northwest, and Southwest. Tibbet's and Stake Bay are always divable. Southeast and Northeast areas get pounded during the winter.
Hopefully you can get to the South Walls or even Little Cayman when the winds calm.
I start at Spot Bay and work west until the swells stop. Usually around Heritage reef it simmers down. Coming up over bluff, if it's breaking in Spot Bay the whole South will be big swells. You can dive, but the exits involve clawing up the iron shore and taking the hits. Definitely give it a go, no crowds and the rough water doesn't affect the vis too much. Plus the Nassau Groupers are congregating that time of year all along the south and are awesome.
The valet diving at Brac Scuba Shack and Reef divers is special. However, I seldom see the dive boats venture more than a 1/2 mile from the resort in either direction. I like diving Brac from shore. Swim out to MV Tibbets, shore dive Public Beach,and then a night dive a Nina's Miniwall. And that's only the first day of diving..
If you can't find a spot to dive on Brac, then you are stuck at the bar.
Have fun