Bar Harbor weather in August

Bar Harbor's forum calls August warm and sunny by day, mid-to-high 70s°F, cooling into the 60s at night — genuinely pleasant, which is exactly why it's the busiest month of the year here. Regulars' standard packing list covers both shorts and a light jacket for cooler evenings, plus a rain layer just in case, and note the ocean itself stays cold, 55-60°F, even at the height of summer.

Regulars are specific this month can swing hard from one day to the next, a beautiful sunny, warm day just as likely to be followed by a cold, overcast and blustery one, layers - a long-sleeve shirt, fleece and a windbreaker - the standard advice for exactly that reason. Our row backs that cool, genuinely wet read, 14.3C over 6.7C nights feeling 4C, with a substantial 116.7mm of rain across 9.6 days and a real 21 kph wind. Regulars are consistent hiking stays genuinely wonderful even into the last week of the month, cool, crisp mornings giving way to a comfortable afternoon in the teens Celsius. The casual lobster shacks close for the season by this point, though plenty of sit-down restaurants stay open for a proper lobster dinner. The record: 7.1 hours of sun, humidity 78 percent and AQI 32.

Regulars split the month in two: early May is barely spring, cold and rainy with trees just leafing out, while the last week or so brings lilacs, fully unfurled leaves and genuinely pleasant afternoons. Our row backs the cool start, 14.4C over 6.1C nights feeling 3C, with 86.8mm of rain across 9.6 days and a trace of leftover snow, 0.6cm. Evenings still call for a sweatshirt or light jacket, especially at the top of Cadillac Mountain where the wind cuts noticeably harder than in town. Business timing follows a similar split: most shops and restaurants open by Mother's Day, but the casual roadside lobster shacks hold out until Memorial Day weekend. The trade for coming now rather than September is crowds - noticeably thinner, even if the weather itself is less reliable. The sea sits at a cold 9.2C. The record: humidity 78 percent, 9.5 hours of sun and AQI 38.

Regulars call mid-September one of the best times here, with the summer traffic gone and the weather still good, and they name the crowd that replaces it: autumn brings cruise ships into Bar Harbor, and the fix is to be out early, before the tenders come down. Their range - mid-60s to mid-80s by day, evenings cool but not cold - brackets our 19.1C over 11.3C. Rain is concentrated rather than constant at 93.1mm across 6.6 days, fourteen millimetres each. October is prettier for leaves and busier for it, but still quieter than July and August. The record: humidity 81 percent, 8.8 hours of sun, a 17.7C sea and AQI 37.

June on Mount Desert Island is a trade-off and regulars set it out precisely. Early June is the emptiest and also the worst of it: black flies, and the foggiest stretch of the year alongside May, with morning fog that ruins sunrise plans. The flies are usually gone by the third week, the weather improves through the month, and the summer crowds do not arrive in Acadia until the 4th of July - so late June is the window where everything lines up. Being on the island helps either way, since salt air and breeze keep the flies down near the water. Our row gives 18.5C over 10.8C at 82 percent humidity with 90.4mm across 9.3 precipitation days, the wettest month of the local summer. The sea is 13.6C. The record: 10.3 hours of sun, 15.5 hours of daylight and AQI 40.