Summer is a great time to visit the city of Boston owing to amiable air temperatures, which are actually quite hot, yet tempered by cooler sea breezes. June also brings the season of showers and thunderstorms which could create some inconveniences.
July is considered the warmest and driest month. However, this is a rather relative claim, taking into consideration Boston does not have a dry season at all. Just comparing to other months, the rainfalls are less frequent. August is a quite nice time to travel to Boston too. It's warm and cloudless, even though short showers and thunderstorms are a common thing.