The last days of the 2021 Summer season start off Monday with a taste of early Autumn: near seasonable temperatures in the low-mid 70's for highs, and a continued cool and dry night with lows near 50. It's all about the "Dew Point" Temperatures (Td). Right now they're in the upper 40's to low 50's (the temperature at which 'dew' happens = 100% humidity - a better day or night indicator of the concentration of water droplets suspended in the atmosphere). We can thank that bubble of fair weather 'High Pressure' over New England for that.
However, as that 'High' slips off the coast, a southwest flow of air will start allowing in higher-humidity air and warmer temperatures. That won't happen until Tuesday evening, and particularly Wednesday, after the warm front pushes through, leaving us with hazy filtered sun, Td in the upper 60's to boot, and highs in the upper 70's. Officially the Autumn season begins at 3:21 p.m. Wednesday.
Some showers are possible, most likely on Thursday and/or Friday.