Weather in Boston 🇺🇸
Monthly weather averages & travel planning
September
Avg Temp
23°C
Rain Days
8 days
Sun Hours
9 hrs
Humidity
65%
North America › 🇺🇸 United States › Boston
Updated: March 2026
Is September a Good Time to Visit Boston?
7/10
Good
September is a good time to visit Boston (7/10). With 9 daily sunshine hours and only 8 rain days, this month delivers genuinely reliable outdoor conditions, ranking it 6th sunniest of the year in Boston. Culture-focused travellers and those who prefer lighter crowds will find September a practical choice, with prices running lower than peak July without sacrificing all the good weather. October offers a similar profile at lower hotel rates if dates are flexible. The main practical note: Boston's popular sites are busiest between 10am and 3pm regardless of season. Arriving at opening time or after 4pm makes a significant difference to the experience. Planning tips: accommodation is generally available without long lead times, and flight prices are typically lower than peak season. Flexible travellers will find the best deals by booking 2-4 weeks ahead. Mid-week arrivals consistently unlock lower hotel rates than weekend check-ins.
vs August:27°C avg high
Boston's September weather is shaped by atmospheric forces that make the data more than just numbers. The 23°C average high reflects a transitional pressure pattern where mid-latitude westerlies alternately bring mild maritime air and cooler polar intrusions. As a result, 9 daily sunshine hours are recorded on average, and rainfall of 90mm is distributed across approximately 8 days because precipitation events tend to be frequent but short-lived.
23°C
73°F
Avg High
15°C
59°F
Avg Low
8 days
90 mm total
Rain Days
9h
per day avg
Sunshine
65%
Moderate
Humidity
Temperature in Boston in September
The 8°C day-night temperature range is typical for continental climates: a light jacket in the morning that you shed by midday and need again after sunset. Humidity averages 65%, which is comfortable for most visitors. On warmer days, lighter fabrics help with the mild stickiness in the afternoon. UV index averages 6 this month, classed as moderate. Sunscreen is a sensible precaution for extended outdoor time, particularly at midday. Wind averages 18 km/h, light enough to be refreshing on warm days but noticeable in open coastal areas or elevated viewpoints. In Fahrenheit: 73°F average high, 59°F overnight low. Data sourced from Open-Meteo ERA5 climate reanalysis (1991–2020 normals).
Temperature Trends
High
Low
Rainfall (mm)
0-20 mm21-50 mm51-100 mm100+ mm
What to Wear in Boston in September
Morning15°CBefore the day warms up
Afternoon23°CPeak daytime temperature
Evening18°CAfter sunset cools down
Packing for Boston in September means dressing for 23°C days and 15°C evenings. A light cotton tee with a casual overshirt works well at 23°C, the overshirt doubles as a layer for air-conditioned venues. Evening temperatures settle at 15°C, a modest 8°C drop that a light cardigan or denim jacket covers. Comfortable walking trainers are the versatile choice for both outdoor sightseeing and indoor venues.
Local tip: Layers are more practical than a single heavy garment in Boston. The day-to-evening temperature shift rewards packing a versatile mid-layer you can add or remove as conditions change.
Events in Boston in September
September has no major festivals or public holidays in Boston, which is one of its practical advantages for independent travellers. Attractions run at lower capacity than during peak event periods, queues are shorter, and accommodation is easier to find without needing to book many months in advance. Local restaurants, markets, and transport operate at a relaxed pace, making this an ideal time for visitors who prefer a more authentic, unhurried experience of everyday city life rather than large crowds drawn in by a single major headline event.
What to Pack for Boston in September
Based on 23°C average highs and 8 rainy days
- Light layers for morning and evening
- Breathable T-shirts and comfortable trousers
- UV-protective sunglasses
- SPF 30+ sunscreen
- Comfortable walking shoes (a second pair lets the first air out overnight)
- Universal travel adapter
- Small day pack for city exploration
- Reusable water bottle
Best Activities in Boston in September
- Explore outdoor markets and street food stallsMid-morning (10am-12pm)At 23°C, the temperature is ideal for extended walking without overheating
- Guided walking tour of the historic centreMorning or late afternoonComfortable temperatures allow several hours on foot without fatigue
- Visit rooftop viewpoints and observation decksGolden hour (1 hour before sunset)Warm clear evenings provide exceptional visibility for panoramic photography
- Day trip to the surrounding countryside or coastFull day (depart by 8am)September is reliably dry enough for rural day trips without weather risk
- Afternoon in a world-class museum or galleryAfternoon (2-5pm)Pairs well with outdoor morning activities and provides a mid-day rest from sightseeing
- Coffee-house or traditional cafe culture experienceMid-morning or post-lunchA cultural ritual in this region that rewards slow appreciation regardless of weather
- Evening live music, theatre, or opera performanceEvening shows typically at 7-9pmConsistent evening temperatures make getting to and from evening venues comfortable
- Visit the main botanical garden or city park at seasonal peakYear-round; best light in morningSeptember brings distinct seasonal changes to public green spaces worth exploring
- Try the seasonal farmer's market for local produce and street foodSaturday morning markets typically 8am-1pmSeptember seasonal produce is at peak availability, offering dishes not found at other times of year
Why is Boston mild in September?
September brings the first meaningful shift toward cooler conditions in Boston, as the sun angle drops and day length shortens. Temperatures averaging 23°C by day and 15°C overnight are still comfortable by most standards, but the trend is clearly downward. At 42 degrees north latitude, autumn light has a particular quality: lower in the sky and warmer in tone, it gives the city a photogenic quality quite different from summer. Conditions remain excellent for outdoor activity, and crowds thin compared to the summer peak. Climate data: Open-Meteo ERA5 (1991–2020).
Sunshine Hours
The average number of hours per day with direct sunlight. Calculated from satellite measurements. Days with more than 7 hours of sunshine are ideal for outdoor activities. Under 3 hours means overcast conditions dominate.
UV Index
A scale from 0-11+ measuring ultraviolet radiation intensity. UV 0-2: Minimal risk. UV 3-5: Moderate, wear sunscreen. UV 6-7: High, hat and SPF 30+ essential. UV 8-10: Very High, limit midday exposure. UV 11+: Extreme, seek shade between 10am-4pm.
Rain Days
A rain day is counted when precipitation exceeds 0.1mm. This threshold captures even light drizzle. Unlike total rainfall in mm, rain days tells you how often you might need an umbrella, which is useful for planning outdoor activities.
Humidity
Relative humidity as a percentage. Below 40%: Dry, skin and throat may feel parched. 40-60%: Comfortable, ideal for most people. 60-80%: Sticky, light breathable fabrics recommended. Above 80%: Muggy, heat feels more intense; quick-dry clothing is essential.
Frequently Asked Questions
Boston in September
In September, Boston experiences average highs of 23°C (73°F) and lows of 15°C (59°F). Expect around 8 rainy days and 9 hours of sunshine per day, with humidity averaging 65%. The 8°C gap between daytime and overnight temperatures is worth planning around: light layers work for most visitors during the day, but an overshirt or cardigan handles the cooler evenings. UV index averages 6, so sun protection is advisable on clear days.
Boston typically sees 8 rainy days in September, with total precipitation of around 90mm. Rain is moderate and manageable. Showers tend to pass quickly, and a light rain layer or foldable umbrella is sufficient protection for most days. For context, the driest month in Boston typically sees 4-6 fewer rain days than September.
Pack light layers, a light jacket for evenings, comfortable walking shoes, and sunscreen for Boston in September. Daytime temperatures of 23°C are pleasant, but the evening drop to 15°C means a jacket is essential if you plan to be out after dark. Rain is infrequent with only 8 wet days, so a light rain layer is optional. Comfortable walking shoes are a priority given the amount of ground most visitors cover.
Yes, September is an excellent time to visit Boston. With 9 daily sunshine hours and only 8 rainy days, conditions are ideal for sightseeing and outdoor activities. Temperatures averaging 23°C during the day are comfortable for long walks and outdoor dining. This is peak travel season, so booking accommodation in advance and arriving at popular attractions early in the morning helps avoid the busiest periods.
The average high temperature in Boston in September is 23°C (73°F), and the average low is 15°C (59°F). The mean daily temperature is approximately 19°C (66°F). The day-to-night range of 8°C is moderate, meaning a single light jacket covers most situations. These are 30-year climate normals based on the 1991 to 2020 reference period; individual years will vary, particularly in transitional months like spring and autumn.
The best month to visit Boston is generally July. July offers the most sunshine at 12 hours per day and only 10 rainy days. Average temperatures reach 28°C, making it comfortable for sightseeing, outdoor dining, and exploring the city. If your travel dates are flexible, planning your trip around July gives you the best chance of dry, bright weather.
September is shoulder or low season in Boston, meaning fewer tourists and generally lower prices than peak months. With 9 sunshine hours and 8 rainy days, the weather is less of a draw for mass tourism. This is an advantage for travellers who prefer a quieter, more relaxed experience with shorter queues and easier accommodation availability.
In September, Boston suits a range of activities thanks to mild temperatures around 23°C. Mix of indoor and outdoor activities works well given the moderate chance of rain. Top options include exploring historic neighbourhoods, visiting museums and galleries, local food markets, and day trips to surrounding areas. With 9 hours of sunshine, parks and waterfront walks are particularly enjoyable.
September ranks 6th sunniest of the year in Boston, with an average 9 daily sunshine hours. The driest months are September, February, and August. July is the hottest month (28°C avg high); January is the coolest (2°C). From here, temperatures fall 7°C into October. Compared to last month (August: 27°C high, 9 rain days), September is cooler and drier. September sits in the middle of the annual sunshine ranking for Boston, offering a reasonable balance of good weather and manageable crowds.
Year-Round Climate
| Month | High | Low | Rain Days | Sun | Details |
|---|---|---|---|---|---|
| January | 2°C | -6°C | 10 | 6h | View |
| February | 3°C | -6°C | 9 | 7h | View |
| March | 7°C | -2°C | 11 | 8h | View |
| April | 14°C | 4°C | 11 | 9h | View |
| May | 19°C | 10°C | 11 | 10h | View |
| June | 25°C | 15°C | 10 | 11h | View |
| July | 28°C | 19°C | 10 | 12h | View |
| August | 27°C | 18°C | 9 | 11h | View |
| September | 23°C | 15°C | 8 | 9h | View |
| October | 16°C | 9°C | 10 | 8h | View |
| November | 10°C | 3°C | 10 | 6h | View |
| December | 5°C | -2°C | 11 | 6h | View |
January
10 rain days, 6h sun
2°-6°
February
9 rain days, 7h sun
3°-6°
March
11 rain days, 8h sun
7°-2°
April
11 rain days, 9h sun
14°4°
May
11 rain days, 10h sun
19°10°
June
10 rain days, 11h sun
25°15°
July
10 rain days, 12h sun
28°19°
August
9 rain days, 11h sun
27°18°
September
8 rain days, 9h sun
23°15°
October
10 rain days, 8h sun
16°9°
November
10 rain days, 6h sun
10°3°
December
11 rain days, 6h sun
5°-2°
Other Months in Boston
Plan Your Trip to Boston
Nearby Destinations
Cities within 500 km with comparable weather conditions
Data Sources for Boston
Climate normals represent 30-year averages (1991-2020). Individual years may vary.