Water temperature in Monroe Harbor (IL) in September
Is it warm enough to swim in Monroe Harbor in September? Average water temperature in Monroe Harbor in September is 69.1°F and therefore suitable for comfortable swimming. The warmest water in Monroe Harbor in September is 75.2°F, and the coldest is 62.4°F. To find out the sea temperature today and in the coming days, go to Current sea temperature in Monroe Harbor
Changes water temperature in Monroe Harbor in September 2025, 2024
To get an accurate forecast for the water temperature in Monroe Harbor for any chosen month, compare two years within a 10 year range using the chart below. In addition to the sea water temperature in Monroe Harbor, 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 | 71.1°F | 75.2°F | 64.2°F | 75.2°F |
| September 2 | 71.1°F | 73.9°F | 67.5°F | 74.5°F |
| September 3 | 71.2°F | 73.8°F | 67.6°F | 74.1°F |
| September 4 | 70°F | 73.6°F | 65.8°F | 74.1°F |
| September 5 | 68.5°F | 73.2°F | 64.6°F | 74.5°F |
| September 6 | 69.3°F | 73.2°F | 64.6°F | 74.7°F |
| September 7 | 68.4°F | 72.5°F | 64.6°F | 73.6°F |
| September 8 | 68.2°F | 71.2°F | 64.4°F | 72.3°F |
| September 9 | 68.2°F | 70.3°F | 64.8°F | 72.1°F |
| September 10 | 66.7°F | 70.3°F | 66.4°F | 73°F |
| September 11 | 67.6°F | 70.3°F | 66.6°F | 72.7°F |
| September 12 | 68.9°F | 71.1°F | 66.6°F | 72°F |
| September 13 | 68.5°F | 70.5°F | 65.5°F | 70.9°F |
| September 14 | 69.3°F | 71.4°F | 65.5°F | 71.4°F |
| September 15 | 69.6°F | 71.8°F | 65.5°F | 71.8°F |
| Day | 2025 | 2024 | Min | Max |
|---|---|---|---|---|
| September 16 | 69.8°F | 72.5°F | 62.6°F | 72.5°F |
| September 17 | 70.2°F | 72.1°F | 63.5°F | 72.1°F |
| September 18 | 70.2°F | 72°F | 64°F | 72°F |
| September 19 | 69.8°F | 72.1°F | 63.9°F | 72.1°F |
| September 20 | 68.2°F | 72°F | 64°F | 72°F |
| September 21 | 70°F | 72.5°F | 63.3°F | 72.5°F |
| September 22 | 68.7°F | 72.1°F | 62.4°F | 72.1°F |
| September 23 | 68.7°F | 71.1°F | 62.6°F | 71.2°F |
| September 24 | 69.8°F | 70.3°F | 62.8°F | 71.2°F |
| September 25 | 68.7°F | 69.8°F | 63.5°F | 70.9°F |
| September 26 | 69.8°F | 63.5°F | 70.5°F | |
| September 27 | 69.3°F | 63.7°F | 69.8°F | |
| September 28 | 68.5°F | 63.1°F | 69.4°F | |
| September 29 | 68.7°F | 62.6°F | 68.7°F | |
| September 30 | 69.1°F | 63.1°F | 69.1°F |
Average water temperature in Monroe Harbor in September over a decade
| 2015 | 2016 | 2017 | 2018 | 2019 |
| 68°F | 70.2°F | 68.9°F | 70.2°F | 65.8°F |
| 2020 | 2021 | 2022 | 2023 | 2024 |
| 68.2°F | 69.4°F | 70.3°F | 69.8°F | 71.4°F |
Monroe Harbor sea state in September
Chart comparing the height of waves in Monroe Harbor 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.
Monroe Harbor water temperature during other months:
You can also view information about water temperature for other months by clicking on the month button below
