Having sailed on the Gulf Coast of Florida for more than 20 years I can attest that the heat and humidity can be quite oppressive in the late spring, summer, and early fall. It is stifling in a drifter. I won't be wearing a life jacket in those conditions on my 31 ft boat. We must wear them in the small boat races (I won't get in the boat without it) and the amount of water sweated out in just a few hours is impressive.
One June day I was foredeck crew on a Catalina 30. We were doing 1nm windward-lewards in 15 knots of wind on a bright sunny day. The temperature was in the mid 90s, as was the humidity. My theory was the race committee were sadists. By the time the spinnaker was hauled down, repacked, and the lines re-run, it was time to set it again. In 2 hrs I drank more than a gallon of water, and passed out on the foredeck due to dehydration. (They thought it was a heart attack. It wasn't until the ambulance got me to the hospital and they took fluid samples did they realize the real problem.) I wasn't wearing a life jacket. I was wearing a manually activated jacket in a belt pack. A jacket would have made it worse.
I've never worn any brand/style of life jacket that could be called comfortable. It the heat-humidity it can be unbearable.
