September weather forecastIsle Royale National Park, MI

Calm evening waters at the Rock Harbor in Isle Royale National Park, Michigan, USA

September

Weather in September

September marks the onset of autumn in Isle Royale National Park, Michigan. A noticeable temperature drop from August brings in the distinct autumn chill. Despite the decrease, the weather remains pleasantly warm during daylight hours. The trend of rainfall continues from the last month, keeping the moisture intact. The average temperatures range from 45°F (7.2°C) to 63°F (17.2°C), adding to the pleasant autumn feel.

Temperature

The transition into September in Isle Royale National Park indicates a reduction in the average high-temperature, down to an enjoyable 62.6°F (17°C) from August's pleasant 71.6°F (22°C). Isle Royale National Park experiences a mean low-temperature of 44.6°F (7°C) during September.

Rainfall

September is the month with the most rainfall in Isle Royale National Park. Rain falls for 13 days and accumulates 3.39" (86mm) of precipitation.

Ocean temperature

In September, the average ocean temperature in Isle Royale National Park is 53.6°F (12°C).
Note: Swimming in 53.6°F (12°C) feels unbearing at 55.4°F (13°C) and can be life-risking below 50°F (10°C), causing breathing issues and cold shock, depending on a person's capacity.

Daylight

In Isle Royale National Park, the average length of the day in September is 12h and 34min.
On the first day of the month, sunrise is at 7:14 am and sunset at 8:36 pm. On the last day of September, in Isle Royale National Park, sunrise is at 7:54 am and sunset at 7:36 pm EDT.

Sunshine

The average sunshine in September is 6h.

UV index

The average daily maximum UV index in September is 5. A UV Index estimate of 3 to 5 represents a medium health hazard from exposure to the Sun's UV radiation for the average person.
Note: In September, an average UV index of 5 transforms into the following instructions:
Put precautions into practice - Guidance to elude sunburn is provided. To prevent harmful UV exposure, minimize direct contact with the Sun around midday. Employ a hat with a wide brim for robust protection, cutting UV exposure by half.

Updated: Feb 12, 2024
Published by: Weather U.S. | About Us
Data Sources | Weather Forecasting & Climate

Frequently asked questions

In Isle Royale National Park, 62.6°F (17°C) is the average high-temperature and 44.6°F (7°C) is the average low-temperature during September.

September is the month with the most rainfall. Rain falls for 13 days and accumulates 3.39" (86mm) of precipitation.

In Isle Royale National Park, Michigan, in September, it is raining for 13 days, with typically 3.39" (86mm) of accumulated precipitation.

In Isle Royale National Park, Michigan, the average seawater temperature in September is 53.6°F (12°C). At temperatures below 50°F (10°C), swimming in a suitably protected swimsuit is feasible; otherwise, cold shock and loss of breathing control are imminent. Even a short swim, without thermal protection, at temperatures around 55.4°F (13°C) is not comfortable.

In September, the average day length is 12h and 34min.

On the first day of September in Isle Royale National Park, sunrise is at 7:14 am and sunset at 8:36 pm. On the last day of the month, sunrise is at 7:54 am and sunset at 7:36 pm EDT.

In Isle Royale National Park, Michigan, the average sunshine duration in September is 6h.

In Isle Royale National Park, the average daily maximum UV index in September is 5. A UV Index estimate of 3 to 5 represents a medium health risk from exposure to the Sun's UV radiation.

Today

Tomorrow

Long-term

Year J F M A M J J A September O N D

Aug

September

Oct

Average high temperature

72°F

63°F

52°F

Average low temperature

Average rainfall

Average rainfall days

Average sea temperature

Average daylight

Average sunshine

Average UV index

Average temperature in September
Isle Royale National Park, MI

Average high temperature in September: 63°F

The warmest month (with the highest average high temperature) is July (75°F).
The month with the lowest average high temperature is January (18°F).

Average low temperature in September: 45°F

The month with the highest average low temperature is July (54°F).
The coldest month (with the lowest average low temperature) is January (0°F).

Average rainfall in September
Isle Royale National Park, MI

Average rainfall in September: 3.4"

The wettest month (with the highest rainfall) is September (3.4").
The driest month (with the least rainfall) is February (1.5").

Average rainfall days in September
Isle Royale National Park, MI

Average rainfall days in September: 13 days

The months with the highest number of rainy days are June and September (13 days).
The months with the least rainy days are February and April (8 days).

Average sea temperature in September
Isle Royale National Park, MI

Average sea temperature in September: 54°F

The best month for swimming (with the highest average sea temperature) is August (55°F).
The coldest months (with the lowest average sea temperature) are January, February, March and April (36°F).

Average daylight in September /
Average sunshine in September
Isle Royale National Park, MI

Average daylight in September: 12h and 36min

The month with the longest days is June (Average daylight: 16h and 0min).
The month with the shortest days is December (Average daylight: 8h and 30min).

Average sunshine in September: 6h

The month with the most sunshine is July (Average sunshine: 10h).
The months with the least sunshine are November and December (Average sunshine: 3h).

Average UV index in September
Isle Royale National Park, MI

Average UV index in September: 5

The months with the highest UV index are June and July (UV index 7).
The months with the lowest UV index are January, February, November and December (UV index 1).