Hottest (avg)
#3 / 12
One of the warmer months.
September in context
How it compares to the rest of the year in Seattle.
Wettest (avg)
#9 / 12
Typical rainfall for the year.
Daylight Hours
#6 / 12
Around the yearly average.
Windiest (avg)
#10 / 12
Usually calmer than most months.
Highest UV
#6 / 12
Near the middle of the yearly UV range.
Most Humid
#8 / 12
Humidity stays close to the yearly norm.
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)
- 6
- Typical sun hours
- 05:47 - 18:19
Wet-day pattern
Rain & Snow
Typical rainfall
- Rainy days
- 11 days
- Cloud cover (avg)
- 52%
Air feel
Humidity & Wind
76%
Average humidity
- Wind (avg)
-
- Wind (max gusts)
-
Historical daily baseline
Daily climate explorer
Pick a day to inspect the usual conditions through September in Seattle. 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 21.3°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
Washout risk Measures: Washout day risk. Observed about 14% of days (4.3 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
4.3 days / month
- Share of days
- ~14% of days
- Upper edge
- Up to ~26mm (P95)
Why this matters
Washout conditions are possible on ~4 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 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 ~86km/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 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 ~86km/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.
Rain Moderate
Rain disruption Measures: Likely rain disruption days. Observed about 15% of days (4.4 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
4.4 days / month
- Share of days
- ~15% of days
- Upper edge
- Up to ~26mm (P95)
Why this matters
Rain disruption risk appears on ~4 days. Outdoor plans can become unreliable, so keep an indoor backup and flexibility around start times.
Cold Moderate
Cold feels-like nights Measures: Cold feels-like nights (min <=5C). 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 ~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.
Show all disruptions (13 more)
Rain High impact
Heavy rain days Measures: Heavy rain days (>=10mm). Observed about 7% of days (2.2 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
2.2 days / month
- Share of days
- ~7% of days
- Upper edge
- Up to ~31mm (P95)
Why this matters
Heavy rain is possible on ~2 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 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
- —
- Upper edge
- Up to ~34mm (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
Very heavy rain Measures: Very heavy rain days (>=25mm). 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 ~47mm (P95)
Why this matters
Very heavy rain is possible on ~0 days. Outdoor plans can become unreliable, so keep an indoor backup and flexibility around start times.
Cloud Minor
Cloudy days Measures: Cloudy days (cloud cover >=60%). Observed about 46% of days (13.8 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
13.8 days / month
- Share of days
- ~46% of days
- Upper edge
- Up to ~98% (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 42% of days (12.5 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
12.5 days / month
- Share of days
- ~42% of days
- Upper edge
- Up to ~19mm (P95)
Why this matters
Measurable rain is possible on ~12 days. Fixed-time outdoor plans are safer with a backup option and flexible timing.
Rain Minor
Rainy hours Measures: Rain-hours signal (>=3h rain). Observed about 35% of days (10.4 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
10.4 days / month
- Share of days
- ~35% of days
- Upper edge
- Up to ~22h (P95)
Why this matters
Several rainy hours are possible on ~10 days. Outdoor plans can become unreliable, so keep an indoor backup and flexibility around start times.
Humidity Minor
High humidity Measures: High humidity days (RH >=80%). 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 ~91% (P95)
Why this matters
High humidity is possible on ~9 days. Comfort and pace can drop quickly, so plan shorter outdoor blocks with air-conditioned backup stops.
Rain Minor
Wet most of day Measures: Wet-most-of-day signal (>=6h rain). Observed about 26% of days (7.7 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
7.7 days / month
- Share of days
- ~26% of days
- Upper edge
- Up to ~23h (P95)
Why this matters
Wet-most-of-day conditions are possible on ~8 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 24% of days (7.3 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
7.3 days / month
- Share of days
- ~24% of days
- Upper edge
- Up to ~99% (P95)
Why this matters
Mostly cloudy skies are possible on ~7 days. Fixed-time outdoor plans are safer with a backup option and flexible timing.
Wind Minor
Gusty days Measures: Gusty days (>=40 km/h). Observed about 14% of days (4.1 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
4.1 days / month
- Share of days
- ~14% of days
- Upper edge
- Up to ~66km/h (P95)
Why this matters
Gusty conditions are possible on ~4 days. Exposed activities and transport links are more likely to be disrupted, so keep sheltered alternatives ready.
Cloud Minor
Overcast days Measures: Overcast days (cloud cover >=95%). 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 ~100% (P95)
Why this matters
Overcast skies are possible on ~2 days. Fixed-time outdoor plans are safer with a backup option and flexible timing.
Visibility Minor
Fog-likely signal Measures: Fog-likely visibility proxy. 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 ~96% (P95)
Why this matters
Fog-likely conditions are possible on ~0 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 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 ~96 (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 ~0 days. Fixed-time outdoor plans are safer with a backup option and flexible timing.
Travel planning FAQ
Frequently asked questions
Quick answers to the weather questions you ask the most.
Is September a good time to visit Seattle?
Typical September days in Seattle reach highs of 20°C (68°F) with nights around 12°C (54°F). It usually feels mild by day and cool after dark. Overall, September sits in the middle of the Seattle climate range.
What are temperatures like in September?
Daytime temperatures in September typically peak near 20°C (68°F), while nights drop to around 12°C (54°F). Expect mild afternoons and cool evenings.
How much does it rain in September?
Rainfall in September averages 65 mm (2.6 in) across roughly 11 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 13 hours of daylight in September. Sunrise is typically around 05:47 and sunset near 18:19. Daylight is fairly typical, with enough time for sightseeing.
How strong is the sun in September?
UV levels are moderate (around 6); sunscreen and sunglasses are still a good idea.
Is it windy in September?
In September, average wind speeds are around 8 km/h (5 mph), with gusts on the windiest days reaching about 43 km/h (27 mph). On the ground, it is it often feels breezy, especially in more exposed spots or along the coast.