Seattle in September
In September, Seattle averages 20°C (69°F) during the day and 12°C (54°F) at night, with frequent rain — about 15 days of the month see precipitation (65 mm total).
ShoulderConditions are comfortable for sightseeing without being sweltering. Plan for unsettled weather and bring rain gear.
It's peak hurricane season in Seattle during September. Travel is possible but expect storm risk, possible flight disruption, and generally lower travel insurance coverage.
How September compares to the rest of the year in Seattle
September is in the middle of the year for warmth in Seattle (4th of 12) and moderately rainy compared to the rest of the year (9th of 12). Daytime temperature runs 5°C above the annual average (15°C). September runs 4°C cooler than August (25°C) and cools 5°C in October (15°C).
September sunrise & sunset in Seattle
Times shown for Seattle local time (America/Los_Angeles), calculated for the 15th of September. They shift by a few minutes day to day across the month.
Photography light in Seattle — September
Golden-hour and blue-hour windows for the 15th of September, in Seattle's local time. Use these for soft warm light (golden) or cool architectural twilight (blue).
📅 When to book — Seattle in September
Travel writers usually only tell you when to go. Here's when to book flights and lodging for the best mix of price and availability, based on September's tier (Shoulder) and Seattle's popularity.
Crowds & pricing — September in Seattle
Seattle is in a shoulder season month — fewer crowds, slightly lower prices, and a calmer atmosphere than peak weeks. Most major sights stay open with normal hours, though a handful of seasonal restaurants or boat trips may run reduced schedules. Many regulars consider these months the best time to visit because you trade a small amount of weather reliability for a much more pleasant on-the-ground experience.
Why this tier: excellent tourism weather peak hazard season (1 active)
Sun & mosquito risk — September in Seattle
UV is a clear-sky sea-level estimate — clouds, altitude, and reflective surfaces (snow, water) shift it ±30%. Mosquito risk is climate-derived only; for current disease advisories (dengue, malaria, zika) check the CDC or WHO travel pages before your trip.
Seattle in other months
| Month | Avg high | Avg low | Rainfall | Rain days | Snow days |
|---|---|---|---|---|---|
| January | 8°C / 47°F | 3°C / 37°F | 182 mm | 21 | — |
| February | 8°C / 46°F | 2°C / 36°F | 125 mm | 21 | — |
| March | 11°C / 52°F | 4°C / 39°F | 123 mm | 20 | — |
| April | 14°C / 57°F | 6°C / 42°F | 93 mm | 19 | — |
| May | 18°C / 65°F | 10°C / 49°F | 56 mm | 16 | — |
| June | 21°C / 70°F | 12°C / 54°F | 50 mm | 14 | — |
| July | 25°C / 76°F | 15°C / 58°F | 16 mm | 8 | — |
| August | 25°C / 76°F | 15°C / 59°F | 27 mm | 10 | — |
| September | 20°C / 69°F | 12°C / 54°F | 65 mm | 15 | — |
| October | 15°C / 59°F | 9°C / 48°F | 138 mm | 18 | — |
| November | 10°C / 50°F | 5°C / 41°F | 178 mm | 21 | — |
| December | 7°C / 45°F | 3°C / 37°F | 185 mm | 20 | — |
Other cities with similar September weather
🌍 See the full ranked list of climate twins for Seattle in September →
Frequently asked questions
How hot is Seattle in September?
In September, Seattle averages a high of 20°C (69°F) and a low of 12°C (54°F) — generally mild and pleasant.
Does it rain a lot in Seattle in September?
September is quite rainy in Seattle, with about 15 rainy days on average.
Is September a good time to visit Seattle?
September is mild and pleasant but on the rainy side. It suits travelers who are comfortable with mild and pleasant weather; check the month-by-month ranking to compare it against the rest of the year.
What should I pack for Seattle in September?
Pack light layers for warm days and cooler evenings, plus a compact umbrella or rain jacket. See the full September packing list for Seattle for a complete, climate-based checklist.
Check the live 10-day forecast and sunrise/sunset.