September is an excellent month at Isle Royale — it ranks 2nd of the twelve here. Expect about 61% fewer visitors than August, the park's peak — 3,309 visits on average. Days run around 65°F by afternoon and 44°F at night, with 12.5 hours of daylight.
September against the park's best
| Month | Verdict | Avg. visits | vs. peak | High | Low | Snow | Daylight |
|---|---|---|---|---|---|---|---|
| September (this page) | Excellent | 3,309 | −61% | 65°F | 44°F | 0" | 12.5 h |
| May (best) | Excellent | 1,404 | −83% | 58°F | 37°F | 0.2" | 15.2 h |
| August (peak crowds) | Good | 8,468 | peak | 73°F | 52°F | 0" | 14.3 h |
Weather figures are for the Rock Harbor area, read from the nearest mainland station across the lake in Minnesota — the Grand Portage station. Visits are 2021–2025 averages; climate normals cover 1991–2020. Conditions vary across the park; check current status before you go.
Common questions
Is September a good time to visit Isle Royale?
Yes — it is one of the best months of the year here. September ranks 2 of 12 at Isle Royale on crowds, weather, daylight, and access together.
How crowded is Isle Royale in September?
About 3,309 recreation visits on average — 61% below August, the park's peak.
How warm is Isle Royale in September?
Average highs around 65°F and lows around 44°F at the Grand Portage station.
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