Water temperature in Portsmouth (NH) in September
Is it warm enough to swim in Portsmouth in September? Average water temperature in Portsmouth in September is 62.8°F and therefore is not suitable for comfortable swimming. The warmest sea in Portsmouth in September is 70.5°F, and the coldest is 57.6°F. To find out the sea temperature today and in the coming days, go to Current sea temperature in Portsmouth
Changes water temperature in Portsmouth in September 2025, 2024
To get an accurate forecast for the water temperature in Portsmouth for any chosen month, compare two years within a 10 year range using the chart below. In addition to the sea water temperature in Portsmouth, 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 | 61.5°F | 66.7°F | 61.5°F | 68.5°F |
| September 2 | 63.1°F | 65.8°F | 62.2°F | 68.5°F |
| September 3 | 63°F | 64.4°F | 61°F | 69.1°F |
| September 4 | 63°F | 64.6°F | 60.6°F | 69.8°F |
| September 5 | 64.8°F | 60.6°F | 70.2°F | |
| September 6 | 64°F | 60.8°F | 70.5°F | |
| September 7 | 64.6°F | 60.8°F | 69.4°F | |
| September 8 | 63.5°F | 60.4°F | 68.7°F | |
| September 9 | 61.9°F | 60.3°F | 68°F | |
| September 10 | 61.7°F | 60.1°F | 68.5°F | |
| September 11 | 61.5°F | 59.9°F | 69.1°F | |
| September 12 | 63°F | 60.3°F | 67.8°F | |
| September 13 | 64.4°F | 60.3°F | 69.1°F | |
| September 14 | 63.9°F | 60.6°F | 67.6°F | |
| September 15 | 64.9°F | 59.7°F | 65.7°F |
| Day | 2025 | 2024 | Min | Max |
|---|---|---|---|---|
| September 16 | 64.8°F | 59.5°F | 66°F | |
| September 17 | 64.2°F | 59.2°F | 66.4°F | |
| September 18 | 64.4°F | 59°F | 66.2°F | |
| September 19 | 64.2°F | 59°F | 65.1°F | |
| September 20 | 63.3°F | 58.8°F | 64.4°F | |
| September 21 | 62.8°F | 58.8°F | 64.6°F | |
| September 22 | 62.1°F | 58.6°F | 64.6°F | |
| September 23 | 61.3°F | 58.3°F | 64.9°F | |
| September 24 | 61.2°F | 57.9°F | 65.5°F | |
| September 25 | 61°F | 57.6°F | 65.1°F | |
| September 26 | 60.8°F | 57.7°F | 64.8°F | |
| September 27 | 61.5°F | 58.1°F | 64.2°F | |
| September 28 | 60.4°F | 58.3°F | 63.9°F | |
| September 29 | 61.7°F | 58.6°F | 63.3°F | |
| September 30 | 61.2°F | 58.6°F | 62.8°F |
Average water temperature in Portsmouth in September over a decade
| 2015 | 2016 | 2017 | 2018 | 2019 |
| 64°F | 63.7°F | 61.3°F | 65.3°F | 63.3°F |
| 2020 | 2021 | 2022 | 2023 | 2024 |
| 62.4°F | 64.8°F | 62.6°F | 64.6°F | 63.1°F |
Portsmouth sea state in September
Chart comparing the height of waves in Portsmouth 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.
Portsmouth water temperature during other months:
You can also view information about water temperature for other months by clicking on the month button below
