Weather will likely play an important role when you plan your trip to Boston, and keep in mind that cheaper options are usually available when the weather isn't as good. The hottest months are usually September and August with an average temp of 79°F, while the coldest months are February and March with an average of 77°F. The rainiest months in Boston are January, May, June, and November, with each month seeing an average of 15 inches of rainfall.