Hottest (avg)
#4 / 12
Sits around the middle of the year.
September in context
How it compares to the rest of the year in Boston.
Wettest (avg)
#6 / 12
Typical rainfall for the year.
Daylight Hours
#6 / 12
Around the yearly average.
Windiest (avg)
#9 / 12
Close to the yearly wind average.
Highest UV
#6 / 12
Near the middle of the yearly UV range.
Most Humid
#1 / 12
The muggiest month of the year.
Monthly climate breakdown
A detailed look at the typical climate conditions for September.
Thermal profile
Temperature
Typical daytime high
- Nighttime low
-
- Feels like (avg)
-
Light window
Sunshine
12.5 h
Average daylight
- UV index (max)
- 7
- Typical sun hours
- 05:24 - 17:53
Wet-day pattern
Rain & Snow
Typical rainfall
- Rainy days
- 10 days
- Cloud cover (avg)
- 52%
Air feel
Humidity & Wind
75%
Average humidity
- Wind (avg)
-
- Wind (max gusts)
-
Historical daily baseline
Daily climate explorer
Pick a day to inspect the usual conditions through September in Boston. Based on a 30-year historical climate baseline, not a forecast.
Primary control
Select a day
Scroll to compare daily conditions. The summary updates with your selection.
Secondary context
Monthly trend
Median daytime highs across the month, with a softer low line.
Median temperatureMedian lowTypical range
Day 15 selected for September. Temperature 22.6°C.
Historical disruption baseline
Typical disruptions in September
Based on 30 years of historical data, these are the disruption patterns most likely to affect plans in September.
Rain High impact
Rain disruption Measures: Likely rain disruption days. Observed about 17% of days (5.1 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
5.1 days / month
- Share of days
- ~17% of days
- Upper edge
- Up to ~51mm (P95)
Why this matters
Rain disruption risk appears on ~5 days. Outdoor plans can become unreliable, so keep an indoor backup and flexibility around start times.
Rain High impact
Washout risk Measures: Washout day risk. Observed about 16% of days (4.7 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
4.7 days / month
- Share of days
- ~16% of days
- Upper edge
- Up to ~52mm (P95)
Why this matters
Washout conditions are possible on ~5 days. Outdoor plans can become unreliable, so keep an indoor backup and flexibility around start times.
Rain High impact
Heavy rain days Measures: Heavy rain days (>=10mm). Observed about 9% of days (2.8 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
2.8 days / month
- Share of days
- ~9% of days
- Upper edge
- Up to ~67mm (P95)
Why this matters
Heavy rain is possible on ~3 days. Outdoor plans can become unreliable, so keep an indoor backup and flexibility around start times.
Wind High impact
Strong gusts Measures: Strong gust days (>=60 km/h). Observed about 4% of days (1.1 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
1.1 days / month
- Share of days
- ~4% of days
- Upper edge
- Up to ~90km/h (P95)
Why this matters
Strong gusts are possible on ~1 days. Exposed activities and transport links are more likely to be disrupted, so keep sheltered alternatives ready.
Wind High impact
Stormy conditions Measures: Storm-impact proxy days. Observed about 3% of days (1.0 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
1.0 days / month
- Share of days
- ~3% of days
- Upper edge
- Up to ~75km/h (P95)
Why this matters
Stormy conditions are possible on ~1 days. Exposed activities and transport links are more likely to be disrupted, so keep sheltered alternatives ready.
Visibility Moderate
Fog-likely signal Measures: Fog-likely visibility proxy. Observed about 8% of days (2.3 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
2.3 days / month
- Share of days
- ~8% of days
- Upper edge
- Up to ~98% (P95)
Why this matters
Fog-likely conditions are possible on ~2 days. Fixed-time outdoor plans are safer with a backup option and flexible timing.
Show all disruptions (25 more)
Rain High impact
Very heavy rain Measures: Very heavy rain days (>=25mm). Observed about 3% of days (0.9 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
0.9 days / month
- Share of days
- ~3% of days
- Upper edge
- Up to ~77mm (P95)
Why this matters
Very heavy rain is possible on ~1 days. Outdoor plans can become unreliable, so keep an indoor backup and flexibility around start times.
Rain High impact
Washout run Measures: Multi-day washout runs. Observed about 0.8 days/month in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
0.8 days / month
- Share of days
- —
- Upper edge
- Up to ~66mm (P95)
Why this matters
Multi-day washout runs are possible on ~1 days. Outdoor plans can become unreliable, so keep an indoor backup and flexibility around start times.
Rain High impact
Extreme rain Measures: Extreme rain days (>=50mm). Observed about 1% of days (0.3 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
0.3 days / month
- Share of days
- ~1% of days
- Upper edge
- Up to ~81mm (P95)
Why this matters
Extreme rain is possible on ~0 days. Outdoor plans can become unreliable, so keep an indoor backup and flexibility around start times.
Wind High impact
Severe gusts Measures: Severe gust days (>=80 km/h). Observed about 1% of days (0.2 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
0.2 days / month
- Share of days
- ~1% of days
- Upper edge
- Up to ~93km/h (P95)
Why this matters
Severe gusts are possible on ~0 days. Exposed activities and transport links are more likely to be disrupted, so keep sheltered alternatives ready.
Humidity Moderate
Muggy days Measures: Muggy days (dew point >=20C). Observed about 5% of days (1.5 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
1.5 days / month
- Share of days
- ~5% of days
- Upper edge
- Up to ~22°C (P95)
Why this matters
Muggy conditions are possible on ~1 days. Fixed-time outdoor plans are safer with a backup option and flexible timing.
Heat Moderate
Hot days Measures: Hot days (>=30C). Observed about 4% of days (1.3 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
1.3 days / month
- Share of days
- ~4% of days
- Upper edge
- Up to ~35°C (P95)
Why this matters
Hot days are possible on ~1 days. Midday activity often needs adjustment around shade, hydration, and indoor fallback options.
Heat Moderate
Hot feels-like days Measures: Hot feels-like days (>=32C). Observed about 3% of days (1.0 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
1.0 days / month
- Share of days
- ~3% of days
- Upper edge
- Up to ~37°C (P95)
Why this matters
Feels-like heat >=32C is possible on ~1 days. Midday activity often needs adjustment around shade, hydration, and indoor fallback options.
Cold Moderate
Cold feels-like nights Measures: Cold feels-like nights (min <=5C). Observed about 2% of days (0.6 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
0.6 days / month
- Share of days
- ~2% of days
- Upper edge
- Up to ~5°C (P95)
Why this matters
Cold feels-like nights are possible on ~1 days. Long outdoor blocks become harder to sustain, so layer up and keep a warm indoor fallback nearby.
Cloud Minor
Cloudy days Measures: Cloudy days (cloud cover >=60%). Observed about 46% of days (13.9 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
13.9 days / month
- Share of days
- ~46% of days
- Upper edge
- Up to ~100% (P95)
Why this matters
Cloudy skies are possible on ~14 days. Fixed-time outdoor plans are safer with a backup option and flexible timing.
Rain Minor
Wet days Measures: Wet days (>=0.1mm). Observed about 41% of days (12.4 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
12.4 days / month
- Share of days
- ~41% of days
- Upper edge
- Up to ~31mm (P95)
Why this matters
Measurable rain is possible on ~12 days. Fixed-time outdoor plans are safer with a backup option and flexible timing.
Humidity Minor
High humidity Measures: High humidity days (RH >=80%). Observed about 37% of days (11.0 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
11.0 days / month
- Share of days
- ~37% of days
- Upper edge
- Up to ~96% (P95)
Why this matters
High humidity is possible on ~11 days. Comfort and pace can drop quickly, so plan shorter outdoor blocks with air-conditioned backup stops.
Wind Minor
Gusty days Measures: Gusty days (>=40 km/h). Observed about 31% of days (9.3 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
9.3 days / month
- Share of days
- ~31% of days
- Upper edge
- Up to ~68km/h (P95)
Why this matters
Gusty conditions are possible on ~9 days. Exposed activities and transport links are more likely to be disrupted, so keep sheltered alternatives ready.
Rain Minor
Rainy hours Measures: Rain-hours signal (>=3h rain). Observed about 30% of days (9.0 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
9.0 days / month
- Share of days
- ~30% of days
- Upper edge
- Up to ~21h (P95)
Why this matters
Several rainy hours are possible on ~9 days. Outdoor plans can become unreliable, so keep an indoor backup and flexibility around start times.
Cloud Minor
Mostly cloudy days Measures: Mostly cloudy days (cloud cover >=80%). Observed about 28% of days (8.4 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
8.4 days / month
- Share of days
- ~28% of days
- Upper edge
- Up to ~100% (P95)
Why this matters
Mostly cloudy skies are possible on ~8 days. Fixed-time outdoor plans are safer with a backup option and flexible timing.
Rain Minor
Wet most of day Measures: Wet-most-of-day signal (>=6h rain). Observed about 20% of days (5.9 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
5.9 days / month
- Share of days
- ~20% of days
- Upper edge
- Up to ~22h (P95)
Why this matters
Wet-most-of-day conditions are possible on ~6 days. Outdoor plans can become unreliable, so keep an indoor backup and flexibility around start times.
Humidity Minor
Humid days Measures: Humid days (dew point >=18C). Observed about 15% of days (4.5 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
4.5 days / month
- Share of days
- ~15% of days
- Upper edge
- Up to ~21°C (P95)
Why this matters
Humid conditions are possible on ~5 days. Comfort and pace can drop quickly, so plan shorter outdoor blocks with air-conditioned backup stops.
Cloud Minor
Overcast days Measures: Overcast days (cloud cover >=95%). Observed about 15% of days (4.5 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
4.5 days / month
- Share of days
- ~15% of days
- Upper edge
- Up to ~100% (P95)
Why this matters
Overcast skies are possible on ~4 days. Fixed-time outdoor plans are safer with a backup option and flexible timing.
Other Minor
Low visibility proxy: same as fog-likely (RH ≥90% AND cloud ≥95%) — true visibility requires hourly visibility data Measures: Low visibility proxy: same as fog-likely (RH ≥90% AND cloud ≥95%) — true visibility requires hourly visibility data. Observed about 8% of days (2.3 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
2.3 days / month
- Share of days
- ~8% of days
- Upper edge
- Up to ~98 (P95)
Why this matters
Low visibility proxy: same as fog-likely (RH ≥90% AND cloud ≥95%) — true visibility requires hourly visibility data is possible on ~2 days. Fixed-time outdoor plans are safer with a backup option and flexible timing.
Humidity Minor
Convective risk Measures: Convective storm risk proxy. Observed about 6% of days (1.7 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
1.7 days / month
- Share of days
- ~6% of days
- Upper edge
- Up to ~21°C (P95)
Why this matters
Convective risk signal appears on ~2 days. Fixed-time outdoor plans are safer with a backup option and flexible timing.
Heat Minor
Very hot feels-like Measures: Very hot feels-like days (>=35C). Observed about 1% of days (0.4 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
0.4 days / month
- Share of days
- ~1% of days
- Upper edge
- Up to ~38°C (P95)
Why this matters
Very hot feels-like conditions are possible on ~0 days. Midday activity often needs adjustment around shade, hydration, and indoor fallback options.
Heat Minor
Heat stress risk Measures: High heat stress days. Observed about 1% of days (0.4 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
0.4 days / month
- Share of days
- ~1% of days
- Upper edge
- Up to ~38°C (P95)
Why this matters
Heat stress is possible on ~0 days. Midday activity often needs adjustment around shade, hydration, and indoor fallback options.
Wind Minor
Breezy days Measures: Breezy days (mean wind >=25 km/h). Observed about 1% of days (0.4 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
0.4 days / month
- Share of days
- ~1% of days
- Upper edge
- Up to ~34km/h (P95)
Why this matters
Breezy conditions are possible on ~0 days. Exposed activities and transport links are more likely to be disrupted, so keep sheltered alternatives ready.
Heat Minor
Warm nights Measures: Warm nights (min >=22C). Observed about 1% of days (0.3 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
0.3 days / month
- Share of days
- ~1% of days
- Upper edge
- Up to ~23°C (P95)
Why this matters
Warm nights are possible on ~0 days. Fixed-time outdoor plans are safer with a backup option and flexible timing.
Heat Minor
Feels-like heatwave Measures: Feels-like heatwave runs (>=3 days). Observed about 0.1 days/month in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
0.1 days / month
- Share of days
- —
- Upper edge
- Up to ~35°C (P95)
Why this matters
Feels-like heatwave runs are possible on ~0 days. Midday activity often needs adjustment around shade, hydration, and indoor fallback options.
Heat Minor
Heatwave run Measures: Heatwave runs (>=3 hot days). Observed about 0.1 days/month in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
0.1 days / month
- Share of days
- —
- Upper edge
- Up to ~34°C (P95)
Why this matters
Heatwave runs are possible on ~0 days. Midday activity often needs adjustment around shade, hydration, and indoor fallback options.
Travel planning FAQ
Frequently asked questions
Quick answers to the weather questions you ask the most.
Is September a good time to visit Boston?
Typical September days in Boston reach highs of 23°C (73°F) with nights around 14°C (57°F). It usually feels warm by day and cool after dark. Overall, September sits in the middle of the Boston climate range.
What are temperatures like in September?
In September, you can usually expect highs of 23°C (73°F) and lows near 14°C (57°F). That means warm days and cool nights, so pack layers you can add or remove.
How much does it rain in September?
Rainfall in September averages 95 mm (3.7 in) across roughly 10 days. Overall it is a quite rainy time of year, so a light rain jacket and waterproof shoes are very handy.
How many hours of daylight are there in September?
You can expect about 12 hours of daylight in September. Sunrise is typically around 05:24 and sunset near 17:53. Daylight is fairly typical, with enough time for sightseeing.
How strong is the sun in September?
UV levels are often high (around 7). Regular sunscreen and a hat are recommended.
Is it windy in September?
In September, average wind speeds are around 13 km/h (8 mph), with gusts on the windiest days reaching about 50 km/h (31 mph). On the ground, it is it can feel quite windy at times, particularly when weather systems move through.