September Weather in Princeton, United States

Last updated: June 24, 2025

In September, the average temperature in Princeton, United States hovers around 20°C (68°F), with the mercury dipping as low as 4°C (39°F) and soaring up to 34°C (94°F). Expect about 117 mm (4.6 in) of rain spread over 10 days, accompanied by an average humidity of 78%. Whether you're exploring the great outdoors or seeking cozy indoor activities, this month brings a blend of warmth and refreshing showers!

September Temperature in Princeton

In September in Princeton, the average temperature is 20°C (68°F). Maximum temperatures can reach 34°C (94°F), while minimums can dip as low as 4°C (39°F). It's a great time to visit for a mix of warm days and cooler evenings, perfect for outdoor adventures and exploration.

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 20°C (68°F), with highs reaching up to 34°C (94°F) and lows dropping to around 4°C (39°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 117 mm (4.6 in) recorded over a span of 10 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 117 mm (4.6 inches) of precipitation spread over approximately 10 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 78%. With an average temperature of 20°C (68°F), this humidity feels like a warm, enveloping blanket that makes exploring the sights a bit sticky, so travelers should stay hydrated and take frequent breaks in the shade.

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 78%, 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 is 8, which corresponds to a very high Exposure Category. This means that the time to burn is only 15 minutes. For more detailed information, you can refer to 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 8, 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	-5°C (23°F)	55 mm (2.2 inches)	81%	moderate
February Weather	-4°C (26°F)	60 mm (2.4 inches)	81%	moderate
March Weather	4°C (40°F)	88 mm (3.5 inches)	81%	high
April Weather	9°C (49°F)	106 mm (4.2 inches)	82%	very high
May Weather	17°C (62°F)	148 mm (5.8 inches)	78%	very high
June Weather	23°C (73°F)	134 mm (5.3 inches)	81%	extreme
July Weather	25°C (77°F)	85 mm (3.4 inches)	79%	very high
August Weather	23°C (74°F)	81 mm (3.2 inches)	77%	very high
September Weather	20°C (68°F)	117 mm (4.6 inches)	78%	very high
October Weather	12°C (54°F)	112 mm (4.4 inches)	78%	high
November Weather	4°C (39°F)	48 mm (1.9 inches)	87%	moderate
December Weather	0°C (32°F)	48 mm (1.9 inches)	84%	low