A few hot days and the water in Long Island Sound has warmed quickly. The 3-day average water surface temperature from the Ocean Remote Sensing Group and Johns Hopkins Applied Physics Laboratory shows a pool of very warm water in the western 2/3 of the Sound.
25C water temperatures are common from Madison to Greenwich but, as usual, a pocket of much colder water (near 20C) exists around The Race and Fishers Island Sound.
Here are two water temperature traces from New Haven Habor and New London Harbor showing the big disparity from the central Sound and the eastern Sound. You can see a definite diurnal trend in the water temperature in New Haven (warmest water during the evening and coolest around mid morning) while the New London water temperature shows no such trend.
If you're wondering average water temperature peaks in New Haven during August while New London maxes out during the last 15 days of July and first 15 days of August at 75F and 72F, respectively.
The coldest water in summer on the east coast is in Eastport, Maine that peaks at a bone crushing maximum temperature of 51F.