September Weather in Princeton, United States

Last updated: June 24, 2025

In Princeton, United States, the average temperature in September hovers around 19°C (66°F), making it a comfortable month to explore. However, be prepared for temperature fluctuations, with minimums dipping to 2°C (37°F) and maximums climbing to 31°C (88°F). Expect some precipitation as well, with an average of 109 mm (4.3 in) over the course of 9 days. Don’t forget to account for the average humidity of 68%, which can make the air feel a bit muggy at times.

September Temperature in Princeton

In September in Princeton, the average temperature is a pleasant 19°C (66°F). The maximum can reach a warm 31°C (88°F), while the minimum can dip to a chilly 2°C (37°F). It's a great time to travel, as you're likely to experience a mix of warm days and cool evenings, perfect for outdoor adventures and exploring the local sights.

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

The chart illustrates September temperature patterns in Princeton, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Princeton, September typically has an average temperature of 19°C (66°F), with highs reaching up to 31°C (88°F) and lows dropping to around 2°C (37°F).

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

September Precipitation in Princeton

In Princeton in September, the total precipitation amount is 109 mm (4.3 in) spread over 9 days.

September Precipitation Trends in Princeton

The chart displays monthly precipitation patterns in Princeton, 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 Princeton, September typically receives around 109 mm (4.3 inches) of precipitation spread over approximately 9 days.

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

Choose your preferred precipitation unit

Millimeters (mm) Inches (in)

September Humidity in Princeton

In Princeton in September humidity is 68%. With an average temperature of 19°C (66°F), this humidity feels like a warm embrace, creating a sticky atmosphere that can be a bit uncomfortable for traveling.

September Average Humidity in Princeton

This chart illustrates the average monthly humidity levels in Princeton, 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 Princeton is approximately 68%, 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 Princeton

In Princeton in September, the maximum UV index reaches 10, which corresponds to a very high Exposure Category. With a time to burn of just 15 minutes, it's crucial to take precautions. For more detailed information, you can check the Hourly UV Index in Princeton.

Maximum UV Index Levels in Princeton for September

The chart shows the monthly maximum UV Index (UVI) for Princeton 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 Princeton typically reaches 10, which falls under the very high exposure category.

Data source: Princeton 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 Princeton Compares to Other Months

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

This table compares monthly weather conditions in Princeton, 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 (34°F)	77 mm (3.0 inches)	87%	moderate
February Weather	4°C (40°F)	124 mm (4.9 inches)	87%	high
March Weather	7°C (45°F)	100 mm (3.9 inches)	86%	very high
April Weather	11°C (53°F)	120 mm (4.7 inches)	84%	very high
May Weather	17°C (62°F)	133 mm (5.2 inches)	83%	extreme
June Weather	20°C (68°F)	119 mm (4.7 inches)	83%	extreme
July Weather	22°C (72°F)	78 mm (3.1 inches)	79%	extreme
August Weather	21°C (70°F)	109 mm (4.3 inches)	66%	very high
September Weather	19°C (66°F)	109 mm (4.3 inches)	68%	very high
October Weather	14°C (57°F)	115 mm (4.5 inches)	78%	high
November Weather	6°C (43°F)	72 mm (2.8 inches)	89%	moderate
December Weather	4°C (39°F)	96 mm (3.8 inches)	86%	moderate