Water temperature in Seattle (WA) in September
Is it warm enough to swim in Seattle in September? Average water temperature in Seattle in September is 55.9°F and therefore is not suitable for comfortable swimming. The warmest sea in Seattle in September is 60.4°F, and the coldest is 51.4°F. Average high air temperature in Seattle in September is 71°F, and average low temperature is 52°F. To find out the sea temperature today and in the coming days, go to Current sea temperature in Seattle
Changes water temperature in Seattle in September 2025, 2024
To get an accurate forecast for the water temperature in Seattle for any chosen month, compare two years within a 10 year range using the chart below. In addition to the sea water temperature in Seattle, the selected years in the table also show the values of the maximum and minimum temperatures on each of the days of September.
You can choose any other years:
| Day | 2025 | 2024 | Min | Max |
|---|---|---|---|---|
| September 1 | 60.3°F | 59.4°F | 54.3°F | 60.3°F |
| September 2 | 59.7°F | 58.6°F | 54°F | 59.7°F |
| September 3 | 60.1°F | 58.1°F | 53.8°F | 60.1°F |
| September 4 | 59.2°F | 58.3°F | 53.6°F | 59.2°F |
| September 5 | 59.7°F | 59.7°F | 53.4°F | 59.7°F |
| September 6 | 59.5°F | 60.3°F | 53.4°F | 60.3°F |
| September 7 | 57.9°F | 60.4°F | 53.2°F | 60.4°F |
| September 8 | 57.4°F | 60.1°F | 53.4°F | 60.1°F |
| September 9 | 58.5°F | 59.2°F | 53.1°F | 59.2°F |
| September 10 | 57.9°F | 58.1°F | 53.1°F | 59°F |
| September 11 | 57.7°F | 57.6°F | 53.2°F | 59.2°F |
| September 12 | 57.2°F | 58.1°F | 53.4°F | 59°F |
| September 13 | 58.1°F | 58.3°F | 53.4°F | 59.4°F |
| September 14 | 57.6°F | 58.1°F | 53.6°F | 58.8°F |
| September 15 | 58.3°F | 56.5°F | 53.6°F | 58.3°F |
| Day | 2025 | 2024 | Min | Max |
|---|---|---|---|---|
| September 16 | 57.4°F | 57.4°F | 53.4°F | 57.7°F |
| September 17 | 58.5°F | 57°F | 53.4°F | 58.5°F |
| September 18 | 57.7°F | 53.2°F | 57.7°F | |
| September 19 | 56.7°F | 52.9°F | 56.7°F | |
| September 20 | 55.8°F | 54°F | 56.3°F | |
| September 21 | 55.9°F | 52.7°F | 57.2°F | |
| September 22 | 55.6°F | 55.2°F | 56.1°F | |
| September 23 | 56.3°F | 52.7°F | 56.8°F | |
| September 24 | 56.5°F | 52.7°F | 56.7°F | |
| September 25 | 56.7°F | 52.7°F | 57°F | |
| September 26 | 55.4°F | 53.6°F | 56.5°F | |
| September 27 | 54.9°F | 52.7°F | 56.7°F | |
| September 28 | 55.8°F | 53.4°F | 57°F | |
| September 29 | 55.6°F | 52.7°F | 57.4°F | |
| September 30 | 55.2°F | 51.4°F | 56.7°F |
Average water temperature in Seattle in September over a decade
| 2015 | 2016 | 2017 | 2018 | 2019 |
| 56.8°F | 56.5°F | 56.8°F | 56.5°F | 57°F |
| 2020 | 2021 | 2022 | 2023 | 2024 |
| 56.8°F | 56.5°F | 56.7°F | 56.7°F | 57.4°F |
Seattle sea state in September
Chart comparing the height of waves in Seattle in September over the past years. The red line indicates the height of the waves when swimming in the sea is prohibited. To view the current sea conditions, click on the graph.
Weather and climate in Seattle in September
This data display average monthly climate indicators in Seattle in September based on our historical weather readings over a period of ten years. In addition to temperature, we include data on the number of rainy and sunny days so you can have all the information about your destination before your trip
- Average HIGH temperature71°F
- Average LOW temperature52°F
- Average humidity
73 - Average rainfall days8 days
- Average rainfall38mm/1.5''
- Average daylight13h
- Average sunshine7.4h
- Average UV index5
Seattle water temperature during other months:
You can also view information about water temperature for other months by clicking on the month button below
