Nantucket weather in September

September is the month this board recommends over the summer it follows: the crowds thin out, the bike paths empty, and everything is still open. On the water they say it has finally warmed up - our column reads that slightly differently, 19.8C against 19.9C in July and August, so the sea holds its peak while the air steps down to 22.2C days and 15.2C nights. The same swimming with fewer people in it. One thing to plan around: they call September fairly clear and our rain column disagrees, 105.9mm against August's 48.6mm, across only 6.3 days - few storms but large ones, which is what hurricane season does to this coast. The record: humidity 84 percent, a 30.5 kph wind, 8.9 hours of sun and AQI 48.

Regulars are specific that a cold east wind blowing off the water is the real story this month, capable of making even a sunny day feel genuinely chilly regardless of the air temperature on paper. Our row backs that cool, still-breezy read, 16C over 8.8C nights feeling 5C, with 76.8mm of rain across 9.3 days and a real 33 kph wind. Regulars are consistent this counts as shoulder season proper, some visits landing glorious and clear, others turning cold, rainy and foggy with little warning either way. A proper windproof layer matters here as much as anything for warmth, regulars say, more than a heavy coat alone. The sea sits at a cold 12.6C, far too cold for a swim this early. The record: humidity 86 percent, 10 hours of sun and AQI 49.

Nantucket-forum threads on winter and early spring visits call March brutal and usually very windy, cold enough that swimming or sunbathing are entirely off the table, but posters note the island rarely drops to genuinely freezing thanks to its ocean-moderated climate. Most shops and restaurants stay closed for the season, only a handful of inns and eateries operating, so a March visit means a genuinely quiet, scaled-down version of the island rather than the bustling summer one. The upside repeated across threads: the odds of a sunny day climb noticeably compared to deep winter, a real shift from the greyest stretch of the year. A beach walk in proper cold-weather gear is still called worthwhile for anyone drawn to the off-season quiet, even if actual beach activities aren't in play. The record: 7.9C days feeling like 3C, 0.8C nights, 90mm across 7.4 days, 7.2cm of late-season snowfall, a 5.2C sea and wind averaging 42 km/h.

Nantucket has its own name for June - Junuary - for the gloom and the wind, and the month delivers either glorious weather or cold, rain and fog with nothing in between. Our row's 20.5C day over a 13.8C night, at 89 percent humidity with a 29.1 kph wind, is the damp version. Fog is the practical risk because it closes the airport: it is worst in the early morning and early evening, though cancellations are less frequent than the reputation suggests, since the schedules flex around the clear breaks. Crowds arrive in the second half of the month once schools are out, and even then they are confined to a few blocks of town - 70 percent of the island is conservation land. The record: 5.9 precipitation days carrying 60.1mm, 11.3 hours of sun and a 16.2C sea.

Nantucket-forum regulars will not promise an August week: it can be warm and sunny, or it can sit around 70F and rain most days, and fog is a constant through July and August - enough that the standing advice is to treat flights as optional and keep the ferry as the fallback if you get fogged in. On crowds they are more reassuring than the reputation suggests. August is the peak and the most expensive stretch of the year, and cars on the ferry book out well ahead, but so much of island life happens privately that the crush is mostly traffic in town and at the airport. Restaurants want reservations. The record: 25.1C days, 18.2C nights, 5.7 precipitation days, humidity near 88 percent, a 19.9C sea and a 27 kph wind.