It's not just Florida. According to the European Union, the world's average global sea surface temperature hit 20.96C (69.73F) this week, breaking a record set in 2016.
"The water feels like a bath when you jump in," says Dr Kathryn Lesneski, who is monitoring a marine heatwave in the Gulf of Mexico for the National Oceanic and Atmospheric Administration. "There is widespread coral bleaching at shallow reefs in Florida and many corals have already died."
"We are putting oceans under more stress than we have done at any point in history," says Dr Matt Frost, from the Plymouth Marine Lab in the UK, referring to the fact pollution and overfishing also change the oceans.
A chart prepared by the BBC shows that this summer has been an extreme outlier, diverging sharply from the trend lines three months ago. For the global ocean heat cycle, usually at its peak in March, a record being set in August is not just hot, but weird. "The fact that we've seen the record now makes me nervous about how much warmer the ocean may get between now and next March," Dr Samantha Burgess told them.