Having surfed in the PNW, winter water temps are only a few degrees cooler than summer. I suspect the same for Long Island sound etc. But if you have a wet or dry suit, that should not be a problem.
Something else caused his death.
Lake Lewis did not warn appreciably when I was there for ROTC Summer Camp in 1975. It was probably no more than 60 degrees. Quite a few cadets had difficulty completing their tasks in water activities. If you’ve never been exposed to colder water, the initial shock can be difficult to overcome. After three springs at Fort Lewis, I was well prepared.
LI and the New England coast warm up quite a bit in the summer. The Gulf Stream brings the warm water up. So even the Gulf of Maine/NH can warm up to 70 in August/September.
The west coast current comes down from Alaska. So even in Cabo San Lucas the Pacific is cold.