I've been twice at that time period, and both times I thought the weather was super. Maybe a little cool in the morning, high temperatures were in the low/mid 70s. Come to think of it, it might not be swimming weather, depending on what you're used to. I hope you realize that that week is just after the Marathon weekend (the marathon itself is on Sunday). Expect to see some people in the parks wearing one or more medals-"Embracing the clang" (some runners run more than one event, thus have multiple medals, which "Clang" as they walk).