September Weather in Charlestown, United States

Last updated: June 24, 2025

In Charlestown, United States, the average temperature in September hovers around 17°C (62°F). Expect a range that can dip to a chilly -1°C (31°F) and soar to a warm 31°C (89°F). With 79 mm (3.1 in) of precipitation spread over 9 days, the weather can be quite variable. On top of that, the average humidity sits at a comfortable 72%, making it a month of diverse weather experiences!

September Temperature in Charlestown

In September in Charlestown, the average temperature is 17°C (62°F) with maximums that can reach 31°C (89°F) and minimums that can dip as low as -1°C (31°F). This wide range of temperatures suggests that travelers should pack accordingly to enjoy their visit to Charlestown.

September Weather in Charlestown: Daily Temperature Highs, Lows, and Averages

The chart illustrates September temperature patterns in Charlestown, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Charlestown, September typically has an average temperature of 17°C (62°F), with highs reaching up to 31°C (89°F) and lows dropping to around -1°C (31°F).

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

September Precipitation in Charlestown

In Charlestown in September, the precipitation amount is 79 mm (3.1 in) spread over 9 days.

September Precipitation Trends in Charlestown

The chart displays monthly precipitation patterns in Charlestown, 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 Charlestown, September typically receives around 79 mm (3.1 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 Charlestown

In Charlestown in September humidity is 72%. With an average temperature of 17°C (62°F), this humidity feels like a warm embrace, making it perfect for leisurely strolls but potentially heavy on the skin, prompting travelers to seek shade during midday excursions.

September Average Humidity in Charlestown

This chart illustrates the average monthly humidity levels in Charlestown, 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 Charlestown is approximately 72%, 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 Charlestown

In Charlestown 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 Charlestown.

Maximum UV Index Levels in Charlestown for September

The chart shows the monthly maximum UV Index (UVI) for Charlestown 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 Charlestown typically reaches 7, which falls under the high exposure category.

Data source: Charlestown 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 Charlestown Compares to Other Months

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

This table compares monthly weather conditions in Charlestown, showing how September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
	Temperature	Precipitation	Humidity	UV
January Weather	-5°C (23°F)	72 mm (2.9 inches)	89%	moderate
February Weather	-4°C (26°F)	85 mm (3.3 inches)	88%	moderate
March Weather	0°C (32°F)	73 mm (2.9 inches)	86%	high
April Weather	7°C (44°F)	122 mm (4.8 inches)	84%	very high
May Weather	13°C (56°F)	85 mm (3.3 inches)	76%	very high
June Weather	19°C (66°F)	90 mm (3.5 inches)	72%	very high
July Weather	22°C (71°F)	126 mm (5.0 inches)	66%	very high
August Weather	20°C (69°F)	92 mm (3.6 inches)	64%	very high
September Weather	17°C (62°F)	79 mm (3.1 inches)	72%	high
October Weather	10°C (51°F)	142 mm (5.6 inches)	81%	high
November Weather	2°C (36°F)	101 mm (4.0 inches)	87%	moderate
December Weather	-3°C (27°F)	104 mm (4.1 inches)	84%	low