United States Seattle Weather in September (sleeper-best month) — Climate Guide
September (sleeper-best month) in Seattle is Excellent
Seattle Weather in September (sleeper-best month) — Quick Answer
As of 2026- Avg temp
- 21° / 11°
- Rainfall
- 38mm · 7 days
- Crowds
- Busy
As of 2026, Seattle in September (sleeper-best month) averages a high of 21°C and low of 11°C with 38mm of rain over about 7 days. Early autumn — high 21°C, low 11°C. T-shirt + cardigan. Light jacket evenings. Sunglasses.
September (sleeper-best month) is Excellent for Seattle.
**September is the sleeper-best Seattle month.** Weather still warm + mostly dry (similar to August) but hotel rates drop 30% from August + crowds thin. **Bumbershoot Music Festival** (Labor Day weekend) is the city's signature music event. Mt Rainier still accessible (wildflowers ending; foliage beginning).
Travel score
Seattle September (sleeper-best month) Weather Stats
Avg High
21°C
Avg Low
11°C
Rainy Days
7
38mm total
Sunshine
7h
Daily avg
Humidity
70%
Comfortable
UV Index
5
Moderate
Wind
12 km/h
Gusts 25
Sea Temp
13°C
Avg water temp
Crowds
Busy
At attractions
September (sleeper-best month) Sunrise & Sunset
Air Quality
PM2.5
10 μg/m³
PM10
20 μg/m³
Status
Good
Feels-Like Temperature & Wind
Feels like
Daytime
21°C
Nighttime
11°C
Humidity and wind affect how the actual temperature feels.
Wind
12 km/h
Max gust 25 km/h
Activities Recommended for September (sleeper-best month)
September (sleeper-best month) Travel Pros & Cons
Pros
- 21/11°C still warm
- Hotel rates drop 30% from August
- Bumbershoot festival
- Smaller crowds
Cons
- First rains return mid-month
September (sleeper-best month) Events & Festivals
- Bumbershoot Music Festival (Labor Day weekend, Seattle Center)
- Mt Rainier wildflowers ending
Seattle in September (sleeper-best month) — Full Picture
**September is the sleeper-best Seattle month.** Weather still warm + mostly dry (similar to August) but hotel rates drop 30% from August + crowds thin. **Bumbershoot Music Festival** (Labor Day weekend) is the city's signature music event. Mt Rainier still accessible (wildflowers ending; foliage beginning).
What to Wear & What to Pack
Early autumn — high 21°C, low 11°C. T-shirt + cardigan. Light jacket evenings. Sunglasses.
Packing Checklist
Seasonal Weather Overview
Spring (Mar·Apr·May)
14.3°C
6.7°C
13.3/mo
Summer (Jun·Jul·Aug)
22.7°C
12.3°C
5/mo
Autumn (Sep·Oct·Nov)
Current15.7°C
8°C
13/mo
Winter (Dec·Jan·Feb)
8.7°C
3.3°C
17.3/mo
Seattle Monthly Weather Comparison
| Month | High | Low | Rain | Sun | Humid | UV | Crowd | Price |
|---|---|---|---|---|---|---|---|---|
| 8° | 3° | 18d·145mm | 2h | 80% | 1 | Quiet | Low season | |
| 10° | 4° | 16d·110mm | 3h | 78% | 2 | Quiet | Low season | |
| 12° | 5° | 16d·100mm | 4h | 75% | 3 | Moderate | Shoulder | |
| 14° | 6° | 14d·80mm | 5h | 72% | 4 | Moderate | Shoulder | |
| May (Best) | 17° | 9° | 10d·50mm | 7h | 70% | 6 | Busy | Shoulder |
| June (Best) | 20° | 11° | 8d·38mm | 8h | 68% | 7 | Very busy | Peak |
| July (peak month) (Best) | 24° | 13° | 3d·18mm | 10h | 65% | 8 | Very busy | Peak |
| August (Best) | 24° | 13° | 4d·22mm | 9h | 67% | 7 | Very busy | Peak |
| 21° | 11° | 7d·38mm | 7h | 70% | 5 | Busy | Shoulder | |
| 15° | 8° | 13d·90mm | 4h | 75% | 3 | Moderate | Shoulder | |
| 11° | 5° | 19d·175mm | 2h | 80% | 1 | Quiet | Low season | |
| 8° | 3° | 18d·145mm | 2h | 80% | 1 | Busy | Peak |
View Other Months
Seattle September (sleeper-best month) Hotel Picks
Frequently Asked Questions
Is September (sleeper-best month) a good time to visit Seattle?
Seattle in September (sleeper-best month) is Excellent. Tourist crowds are busy and flight/hotel prices are shoulder.
What's the average temperature in Seattle in September (sleeper-best month)?
Seattle September (sleeper-best month) averages a high of 21°C and a low of 11°C.
Does it rain much in Seattle in September (sleeper-best month)?
Seattle September (sleeper-best month) averages 38mm of rainfall over about 7 rainy days.
What should I wear in Seattle in September (sleeper-best month)?
Early autumn — high 21°C, low 11°C. T-shirt + cardigan. Light jacket evenings. Sunglasses.
What time are sunrise and sunset in Seattle in September (sleeper-best month)?
Seattle September (sleeper-best month) sunrise is 06:45 and sunset is 19:25, with 12h 40m of daylight.
What's the air quality like in Seattle in September (sleeper-best month)?
Seattle September (sleeper-best month) air quality (AQI) averages 35, rated Good. PM2.5 averages 10μg/m³.
What activities are recommended in Seattle in September (sleeper-best month)?
In September (sleeper-best month), Seattle is great for Bumbershoot Music Festival, Mt Rainier, Pike Place.
Is September (sleeper-best month) peak season in Seattle?
Seattle September (sleeper-best month) crowds are busy and prices are shoulder. Advance reservations are strongly recommended.
Best Months to Visit Seattle
View Other Months
Planning a September (sleeper-best month) trip to Seattle?
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Why you can trust weather guide
Based in Chiang Mai for 8+ years, with 30+ countries visited across Southeast Asia, Japan, and Europe. Every detail in this guide is primary-source verified as of April 2026, with prices auto-refreshed via live exchange rate APIs. This isn't AI-generated boilerplate — it's written from the perspective of someone who has actually been there.