Water temperature in Half Moon Bay (CA) in September
Is it warm enough to swim in Half Moon Bay in September? Average water temperature in Half Moon Bay in September is 58.6°F and therefore is not suitable for comfortable swimming. The warmest sea in Half Moon Bay in September is 63.9°F, and the coldest is 52.7°F. Average high air temperature in Half Moon Bay in September is 67°F, and average low temperature is 51°F. To find out the sea temperature today and in the coming days, go to Current sea temperature in Half Moon Bay
Changes water temperature in Half Moon Bay in September 2025, 2024
To get an accurate forecast for the water temperature in Half Moon Bay for any chosen month, compare two years within a 10 year range using the chart below. In addition to the sea water temperature in Half Moon Bay, 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 | 58.6°F | 58.6°F | 55.4°F | 62.8°F |
| September 2 | 56.1°F | 57.9°F | 56.1°F | 62.4°F |
| September 3 | 56.5°F | 57.9°F | 55.8°F | 62.2°F |
| September 4 | 56.5°F | 54.9°F | 54.7°F | 62.2°F |
| September 5 | 57°F | 55.9°F | 55.9°F | 62.4°F |
| September 6 | 56.7°F | 54.1°F | 54.1°F | 62.2°F |
| September 7 | 59°F | 54.9°F | 54.9°F | 62.4°F |
| September 8 | 58.5°F | 53.1°F | 53.1°F | 62.2°F |
| September 9 | 59.5°F | 52.7°F | 52.7°F | 62.2°F |
| September 10 | 59.2°F | 53.4°F | 53.4°F | 62.2°F |
| September 11 | 59.7°F | 54.3°F | 54.3°F | 62.4°F |
| September 12 | 59.7°F | 54.1°F | 54.1°F | 62.4°F |
| September 13 | 59.9°F | 55.2°F | 55.2°F | 62.2°F |
| September 14 | 59.9°F | 55.9°F | 55.9°F | 62.2°F |
| September 15 | 60.3°F | 57.4°F | 56.3°F | 62.4°F |
| Day | 2025 | 2024 | Min | Max |
|---|---|---|---|---|
| September 16 | 61°F | 58.3°F | 56.5°F | 63°F |
| September 17 | 60.8°F | 58.5°F | 56.7°F | 63°F |
| September 18 | 61.2°F | 58.6°F | 56.8°F | 63.3°F |
| September 19 | 61.2°F | 56.8°F | 56.7°F | 63.5°F |
| September 20 | 56.8°F | 55.9°F | 63.5°F | |
| September 21 | 55.9°F | 55.9°F | 63.3°F | |
| September 22 | 54.7°F | 54.7°F | 63.7°F | |
| September 23 | 54.9°F | 54.9°F | 63.7°F | |
| September 24 | 56.3°F | 55.6°F | 63.7°F | |
| September 25 | 54.5°F | 54.5°F | 63.5°F | |
| September 26 | 55.6°F | 55.4°F | 63.9°F | |
| September 27 | 56.7°F | 55.4°F | 63.1°F | |
| September 28 | 58.6°F | 55.8°F | 62.6°F | |
| September 29 | 58.1°F | 56.1°F | 62.6°F | |
| September 30 | 58.6°F | 56.3°F | 62.4°F |
Average water temperature in Half Moon Bay in September over a decade
| 2015 | 2016 | 2017 | 2018 | 2019 |
| 61°F | 59°F | 61.2°F | 58.5°F | 58.8°F |
| 2020 | 2021 | 2022 | 2023 | 2024 |
| 58.6°F | 58.8°F | 59°F | 59.2°F | 56.1°F |
Half Moon Bay sea state in September
Chart comparing the height of waves in Half Moon Bay 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 Half Moon Bay in September
This data display average monthly climate indicators in Half Moon Bay 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 temperature67°F
- Average LOW temperature51°F
- Average rainfall days4 days
- Average rainfall10mm/0.4''
Half Moon Bay water temperature during other months:
You can also view information about water temperature for other months by clicking on the month button below
