We've done over 3 dozen dives in Negril in November over Thanksgiving week. Visibility is prisitne, and the water hasn't been choppy at all. Last year, there were 2-3' slow rolling swells and some current, but that's nothing. The current actually led to some nice, easy drift dives. Negril is relatively protected.
There is the potential for choppy waters (dives being cancelled) and reduced visibilty at any time of year. Having said that - we always visit out of hurricane season as we like to dive every day and this obviously reduces the likelyhood of encountering a big storm.
Couples provide a dive service to divers of all levels of experience and age, consequently if there is a risk of injury getting off/on the boat - then the dive boat doesn't go out.
Ian and Vanda