Last updated: June 18, 2025
In September, the average temperature in Thunder Bay, Canada hovers around 13°C (55°F). Expect a chill with minimums dipping to -1°C (31°F), while the mercury can rise as high as 25°C (78°F). Make sure to pack your umbrella, as 98 mm (3.9 in) of precipitation often falls over 13 days. With an average humidity of 76%, be prepared for a damp atmosphere!
In September in Thunder Bay, the average temperature is 13°C (55°F). Maximums can reach 25°C (78°F), and minimums can be as low as -1°C (31°F). This makes Thunder Bay an ideal destination for travelers who enjoy mild weather with occasional warmth and the chance for cooler days.
In Thunder Bay in September, the precipitation amount is 98 mm (3.9 in) over a span of 13 days.
In Thunder Bay in September humidity is 76%. With an average temperature of 13°C (55°F), this humidity feels like a damp, heavy blanket enveloping you, making it feel cooler than it actually is, which can be quite refreshing for short excursions but may also lead to discomfort during prolonged outdoor activities.
In Thunder Bay in September, the maximum UV index is 7, which corresponds to the high Exposure Category. This means that the time to burn is approximately 25 minutes. For more detailed information, you can check the Hourly UV Index in Thunder Bay.
UV Risk Categories
Weather in Thunder Bay varies notably across the year, with each month offering distinct climate conditions. This page compares September’s weather to other months in Thunder Bay, focusing on differences in temperature, rainfall, humidity, and UV levels.
| Temperature | Precipitation | Humidity | UV | |
|---|---|---|---|---|
| January Weather | -13°C (9°F) | 30 mm (1.2 inches) | 95% | low |
| February Weather | -13°C (9°F) | 35 mm (1.4 inches) | 94% | moderate |
| March Weather | -5°C (23°F) | 31 mm (1.2 inches) | 92% | moderate |
| April Weather | 1°C (33°F) | 58 mm (2.3 inches) | 90% | high |
| May Weather | 8°C (47°F) | 52 mm (2.0 inches) | 78% | very high |
| June Weather | 14°C (58°F) | 58 mm (2.3 inches) | 71% | very high |
| July Weather | 19°C (66°F) | 82 mm (3.2 inches) | 70% | very high |
| August Weather | 17°C (63°F) | 77 mm (3.0 inches) | 72% | very high |
| September Weather | 13°C (55°F) | 98 mm (3.9 inches) | 76% | high |
| October Weather | 6°C (43°F) | 87 mm (3.4 inches) | 82% | moderate |
| November Weather | -3°C (27°F) | 51 mm (2.0 inches) | 87% | low |
| December Weather | -9°C (16°F) | 55 mm (2.2 inches) | 94% | low |