Nantucket weather is certainly at its best during the summer. There was a time when tourist activity was largely limited to the summer months, starting after Memorial Day and generally closing down after Labor Day. This is no longer the case, as Nantucket Island is witnessing more tourist activity during the shoulder months of spring and autumn. As a general rule, the Gulf Stream determines Nantucket weather in both the summer and the winter. The Gulf effect renders temperatures an average of 10 degrees warmer in the winter and 10 degrees cooler in the summer. The offshore winds mean that fog is inevitable, but you can count on sunshine about two out of every three days.
Summer: The summer months are the most pleasant time to visit when it comes to temperature. The average high temperatures in the months of June through September hover comfortably between the low to mid-70s and rarely dip below the 60s at night. July and August are the most popular months and provide evidence that many people feel this is the best time to travel to Nantucket. The temperatures are at their warmest during these two months and the Atlantic heats up for swimming. Swimming is no good until July as the temperature of the water is too cold. There are a lot of sunny days and some humidity toward the end of the summer.
Autumn: The average high temperatures in October and November drop into the 50s and there is a greater chance of precipitation, including snow, as it gets closer to the holidays. You probably won’t need a jacket and sweater until October. When the leaves begin to change, the island comes alive with vibrant colors. This is a time that is becoming more popular for visitors of the island. The ocean even stays warm enough to swim through September.
Winter: This is the least busy time in Nantucket, with the exception of the Christmas Stroll and concomitant events leading up to the holiday season. Many repeat visitors of Nantucket find this to be a perfectly charming time to go, but definitely not for time on the beaches. High temperatures in the 30s and low 40s and lows into the 20s.
Spring: The entire island of Nantucket blossoms with amazing vibrancy in the spring and the high temperatures crawl back up into the 50s and 60s. This is a time for rain but the blossoming flora more than makes up for the occasionally soggy weather.