September Weather in Southwest Harbor, United States

Last updated: June 24, 2025

In September, the average temperature in Southwest Harbor, United States hovers around 15°C (59°F), with a minimum dipping to 9°C (48°F) and a pleasant maximum reaching 20°C (69°F). Expect 105 mm (4.2 in) of precipitation spread over about 9 days, coupled with an average humidity of 77%, creating a wonderfully refreshing atmosphere.

September Temperature in Southwest Harbor

In September in Southwest Harbor, the average temperature is 15°C (59°F). Maximums can reach 20°C (69°F), while minimums can be as low as 9°C (48°F). This mild climate makes it an ideal time for outdoor activities and sightseeing.

September Weather in Southwest Harbor: Daily Temperature Highs, Lows, and Averages

The chart illustrates September temperature patterns in Southwest Harbor, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Southwest Harbor, September typically has an average temperature of 15°C (59°F), with highs reaching up to 20°C (69°F) and lows dropping to around 9°C (48°F).

Data source: Temperature data for Southwest Harbor generated using information from the Copernicus Climate Change Service.

September Precipitation in Southwest Harbor

In Southwest Harbor in September, the precipitation amount is 105 mm (4.2 in) over the course of 9 days.

September Precipitation Trends in Southwest Harbor

The chart displays monthly precipitation patterns in Southwest Harbor, with values for each month alongside September’s data, which is highlighted for easy comparison. It shows the amount of precipitation, providing insights into how September’s conditions compare to those of other months. In Southwest Harbor, September typically receives around 105 mm (4.2 inches) of precipitation spread over approximately 9 days.

Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.

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Millimeters (mm) Inches (in)

September Humidity in Southwest Harbor

In Southwest Harbor in September, humidity is 77%. With an average temperature of 15°C (59°F), this humidity feels like a warm blanket enveloping you, making it essential to stay hydrated and choose light, breathable clothing for comfortable travel.

September Average Humidity in Southwest Harbor

This chart illustrates the average monthly humidity levels in Southwest Harbor, with September’s data highlighted for easy comparison. It shows the fluctuation in humidity throughout the year, helping you understand how conditions vary by season. In September, average humidity in Southwest Harbor is approximately 77%, offering insight into how humid the weather typically is during this month.

Data source: Humidity data for September generated using information from the Copernicus Climate Change Service.

September UV Index in Southwest Harbor

In Southwest Harbor 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 Southwest Harbor.

Maximum UV Index Levels in Southwest Harbor for September

The chart shows the monthly maximum UV Index (UVI) for Southwest Harbor in September, representing the highest UV radiation level. The UVI measures the intensity of ultraviolet radiation from the sun, indicating the potential risk of sunburn and UV-related health issues. In September, the maximum UV index in Southwest Harbor typically reaches 7, which falls under the high exposure category.

Data source: Southwest Harbor September UVI data generated using information from the Copernicus Climate Change Service.

UV Risk Categories

Extreme (11+): Avoid the sun, stay in shade.
Very High (8-10): Limit sun exposure.
High (6-7): Use SPF 30+ and protective clothing.
Moderate (3-5): Midday shade recommended.
Low (0-2): No protection needed.

How September Weather in Southwest Harbor Compares to Other Months

Weather in Southwest Harbor varies notably across the year, with each month offering distinct climate conditions. This page compares September’s weather to other months in Southwest Harbor, focusing on differences in temperature, rainfall, humidity, and UV levels.

This table compares monthly weather conditions in Southwest Harbor, showing how September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
	Temperature	Precipitation	Humidity	UV
January Weather	-1°C (30°F)	113 mm (4.4 inches)	88%	low
February Weather	-1°C (31°F)	107 mm (4.2 inches)	88%	moderate
March Weather	1°C (34°F)	83 mm (3.3 inches)	85%	moderate
April Weather	5°C (41°F)	143 mm (5.6 inches)	81%	high
May Weather	8°C (48°F)	105 mm (4.1 inches)	76%	very high
June Weather	12°C (54°F)	95 mm (3.7 inches)	74%	very high
July Weather	15°C (59°F)	82 mm (3.2 inches)	74%	very high
August Weather	16°C (62°F)	87 mm (3.4 inches)	74%	very high
September Weather	15°C (59°F)	105 mm (4.2 inches)	77%	high
October Weather	12°C (54°F)	119 mm (4.7 inches)	82%	moderate
November Weather	6°C (44°F)	139 mm (5.5 inches)	85%	moderate
December Weather	1°C (35°F)	154 mm (6.1 inches)	84%	low