Dido ---- We checked on status of swells before deciding to visit, no idea they could have such an impact. Bay was glass for us all night! thank you for the insite.
We've chartered in BVI for going on 5 years and have NEVER seen the surf that high. We've been in 8 - 12 ft swells sailing from VG to Cane Garden on the north side, but never had that kind of action in a mooring field/anchorage.
The biggest action we saw was when a squall from Hurricane Emily swept through one night. We had lots of warnings; got moored in Sophers Hole early in the evening and rode it out without a problem. Heavy winds passed in 90 min - faster than we could get through a game of Rummikube.
Those on a mooring ball at Diamond Caye and those anchored in harbors at Jost Van Dyke had a bit more exciting evening (VHF listening became the sport of the evening), but most of the problems were due to lack of "seaman skills" - watch the weather, confirm your anchor holding, duck into a sheltered hole for a storm.
BVI's are great cruising grounds. Just be aware that you are not in Disneyland - God and Nature both have a wicked sense of humor...