Isle Royale National Park weather in September
September in Isle Royale National Park: cool, rainy, with clean air — an excellent time to visit.
#4 of 12 months in Isle Royale National Park · #303 of 604 destinations to visit in September · comfort 80/100 (tier A)
Updated June 2026 · climate normals from ERA5 reanalysis
Isle Royale National Park climate normals — September
| Daytime high | 15°C / 60°F | 🙂 cool |
|---|---|---|
| Nighttime low | 13°C / 56°F | |
| Feels like (high) | 13°C / 55°F | |
| Rainfall | 84 mm / 3.3 in | 🌧 rainy |
| Rainy days | 9 days | |
| Humidity | 81% | 💦 very humid |
| Dew point | 11°C / 52°F | |
| Sunshine | 9.4 h/day | |
| Daylight | 12.6 h | |
| Wind | 31 km/h / 19 mph | |
| Air quality (US AQI) | 37 | 🍃 good |
Monthly averages from ERA5 reanalysis. AQI is the mean US Air Quality Index for the month.
Where is Isle Royale National Park?
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Isle Royale National Park in September — FAQ
- Is September a good time to visit Isle Royale National Park?
- September in Isle Royale National Park: cool, rainy, with clean air — an excellent time to visit. It ranks #4 of 12 months for Isle Royale National Park on SeasonMap's comfort score (80/100).
- What is the weather like in Isle Royale National Park in September?
- In September, Isle Royale National Park averages a daily high of 15.4°C and a low of 13.1°C, with about 84.3 mm of rain over roughly 9 rainy days.
- What is the air quality in Isle Royale National Park in September?
- Isle Royale National Park has a mean US Air Quality Index of about 37 in September.