The Ph. are just off the equator. I’ve been in the water in northern Australia and the water was 30c and on the verge of being too warm. Definitely not refreshing, felt like a salty bath tub.
Due to water being a way better conductor of heat than air you lose heat up to 75% faster than in air. Even 30°C warm water can therefore quickly lead to hypothermia if unprotected. Ever seen scuba instructors in warm countries? While their customers would often submerge in nothing but a swimsuit the instructors would often wear 6mm full body wetsuits due to longer exposure. And yet a lot of them are shivering in the evenings.
I've been shivering in the water at 27 degrees Celcius in Australia (diving, no wetsuit, sitting on the bottom). Admittedly I have a very slender build, but clearly 27 degrees is below my equilibrium temperature when not in activity.