Its the wind chill that gets you if you are wet on a cold windy day. Sometimes I go surfing on cold Winter days when the surf isn't too big and brisk offshore winds are grooming the swells. The thermometer might read 32 F, and the sea-surface temp might be in the high 40's. That sounds cold enough already, but the wind chill factor makes it much worse. I usually get cold after about an hour of surfing in those conditions, even though I'm trying to stay moving all of the time, alert and concentrating so that I do not have to sit and wait very long for a wave. Making the post-session sprint back up the beach to my rig, the wind chill just sucks any remaining body heat away, right through 5mm of neoprene. That's why I don't like to be out on my Tarpon in a wetsuit on a cold Winter's day.