Average sea temperatures for Bermuda around that time of year are 68 degrees Fahrenheit, so still on the chilly side of things (relatively speaking!). Air temperatures are beginning to warm, too, but bear in mind that the summer season in Bermuda trends toward what you might find on the U.S. mainland around North and South Carolina in June-August. Should be pleasant beach weather but perhaps a bit nippy for swimming. Apparently the locals don't consider it swimming season until around Bermuda Day, which is at the end of May!