Thunder Bay weather in September 2025

Expect 17°C daytime maximum temperatures in the shade with on average 5 hours of sunshine per day in Thunder Bay in September. Check more long-term weather averages for Thunder Bay in September before you book your next holiday to Ontario in 2025/2026.

  • 17°C maximum daytime temperature in September in Thunder Bay17
    17°C max day temperature
  • 5 hours of sunshine per day
  • 13 days with some rainfall in September in Thunder Bay13
    13 days with some rainfall
  • 6°C minimum night-time temperature in September in Thunder Bay6
    6°C min night temperature
  • 13 hours of daylight per day in September in Thunder Bay13
    13 hours of daylight per day
  • No heat & humidity in September in Thunder Bay0
    No heat & humidity
  • 88 mm monthly rainfall in September in Thunder Bay88
    88 mm of monthly rainfall
  • UV (maximum) index 5 (Moderate) in September in Thunder Bay5
    5 (Moderate) UV index
  • 13°C sea temperature in September in Thunder Bay13
    13°C sea temperature

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The September weather guide for Ontario (Thunder Bay) shows long term weather averages processed from data supplied by CRU (University of East Anglia), the Met Office & the Netherlands Meteorological Institute. Find out more about our data sources.

Metric (°C / mm)  |  Imperial (°F / inches)

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How warm is it in Thunder Bay in September?

Daytime temperatures usually reach 17°C in Thunder Bay in September, falling to 6°C at night.

How sunny is it in Thunder Bay in September?

There are normally 5 hours of bright sunshine each day in Thunder Bay in September - that's 42% of daylight hours.

How warm is the sea around Thunder Bay in September?

The average sea temperature around Thunder Bay in September is 13°C.

Does it rain in Thunder Bay in September?

There are usually 13 days with some rain in Thunder Bay in September and the average monthly rainfall is 88mm.

Thunder Bay September sunrise & sunset times

Browse the sunrise and sunset times for Thunder Bay in September 2025. Select a month to view Thunder Bay sunrise and sunset times for the next 12 months.

JanFebMarAprMayJunJulAugSepOctNovDec

Date Sunrise times Sunset times
Monday, 1st September 2025 06:15 19:38
Monday, 15th September 2025 06:34 19:09
Tuesday, 30th September 2025 06:55 18:37

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