Is September 9-14 too late for summer weather? Mostly sightseeing, shops, restaurants and driving up down Coastline to near Hyannis, Newport, R.I. Maybe day in Boston.
Summer weather is welcome year-round. Not clear what you are asking. You probably won't be spending time on the beach unless it's really hot. Driving around, sure.
Could be 50s in the day. Could be 80s. Will be chilly in the evening.
You know that Rockport is north of Boston and Hyannis (Cape Cod) and Newport are south of Boston, right?
Any of these places can have a cool breeze off the water on any particular day, or there can be a warm land breeze - or no breeze at all. Sun or rain (but no snow in September!)