Weather in Seattle in September
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Book now, pay at pickup — compare Hertz, Avis, Budget, Sixt and 800+ rental companies for September in Seattle.
Compare car hire prices → Affiliate link — we earn a commission at no extra cost to youSeattle in September is pleasantly mild — daytime temperatures average 21.3°C, dropping to 13.1°C at night. The month is moderately rainy (8 rainy days), with roughly 9.3 hours of sunshine a day. This is peak season for good reason — conditions are close to ideal. For the complete picture, see the best time to visit Seattle — every month compared. Once you know when to go, find your Seattle packing list at 247PackingList.
Get ready for Seattle in September
Search flights to Seattle
Compare 100+ airlines for September — one search, best price.
Search Flights →Travel clothing layers
Pack layers — temperatures can vary significantly between day and night.
Check Price →What to pack for Seattle in September
- Light layers
- Sunscreen
- T-shirts and light trousers or shorts
- Light waterproof layer
Compare all months in Seattle
| Month | High | Rain | Rating |
|---|---|---|---|
| January | 8.3°C | 216.0mm | 8/10 |
| February | 8.0°C | 104.8mm | 9/10 |
| March | 10.2°C | 82.6mm | 10/10 |
| April | 13.3°C | 73.7mm | 10/10 |
| May | 17.4°C | 64.7mm | 10/10 |
| June | 20.9°C | 58.6mm | 10/10 |
| July | 24.6°C | 8.0mm | 10/10 |
| August | 24.9°C | 21.5mm | 10/10 |
| September | 21.3°C | 66.1mm | 10/10 |
| October | 15.4°C | 104.4mm | 9/10 |
| November | 10.0°C | 174.8mm | 9/10 |
| December | 7.6°C | 184.1mm | 9/10 |
Full month-by-month guide: best time to visit Seattle →
For facts about United States — currency, language and dialling code — see our United States country guide at 247CountryInfo. Travellers also find it useful to keep a Seattle travel guide to hand. Check clothing sizes in United States before you shop.
Frequently Asked Questions
Is September a good time to visit Seattle?
September rates 10/10 for visiting Seattle — excellent time to visit. Expect average highs of 21.3°C, 66.1mm of rain across the month and about 9.3 hours of daily sunshine.
What is the temperature in Seattle in September?
In September, Seattle has average highs of 21.3°C (70.3°F) and average lows of 13.1°C (55.6°F).
Does it rain in Seattle in September?
Some rain is likely. Seattle averages 66.1mm across about 8 rainy days in September, so a light waterproof layer is worth packing.
What should I wear in Seattle in September?
For Seattle in September (21.3°C highs / 13.1°C lows), pack light layers plus sunscreen, t-shirts and light trousers or shorts, light waterproof layer.
More essentials for Seattle in September
Packing cubes
Keep the bag organised whatever the weather — compression cubes for every size.
Check Price →Travel first aid kit
Compact TSA-friendly kit for peace of mind wherever you travel.
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Climate data sourced from Open-Meteo (open source, open data licence). Monthly averages calculated from 2020–2023 historical data. Weather can be unpredictable — always check a live forecast before travelling.