I am sensitive to high humidity due to Asthma. I was worried about the humidity in Jamaica during November when we went but i just talked to my doctor and brought my extra puffers, i also emailed the nurses at CN about the issue and they got right back to me about their on-site services etc(they happened to have what i would need if it turned to be a problem). So we went mid-november and i didn't have one problem, i found it to be nice and hot but not humid, it didn't bother my breathing at all. Again, i'm not on oxygen so i don't know how high his sensitivity is.
just talk to doc, and email the resort or phone and talk to them.
Couples Negril Nov 13 - 20, 2010