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September Weather in Princeton, United States

Last updated: June 24, 2025

The average temperature in Princeton, United States during September hovers around 20°C (69°F), but be prepared for a temperature range that can dip to a cool 4°C (40°F) or soar to a warm 35°C (95°F). Expect 93 mm (3.7 in) of rainfall over the course of 9 days, contributing to an average humidity of 80%. Dress accordingly and enjoy the unique climate this month brings!

September Temperature in Princeton

In September in Princeton, the average temperature is 20°C (69°F). Maximums can reach 35°C (95°F), and minimums can be as low as 4°C (40°F). This weather makes Princeton an ideal destination for travelers seeking both warmth and cool, refreshing evenings.

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 (69°F), with highs reaching up to 35°C (95°F) and lows dropping to around 4°C (40°F).
JanFebMarAprMayJunJulAugSepOctNovDec252740506373767469553933
Data source: Temperature data for Princeton generated using information from the Copernicus Climate Change Service.
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The average of daily temperatures (24 hours) calculated across all days in the month.

September Precipitation in Princeton

In Princeton in September, the precipitation amount is 93 mm (3.7 in) over the course of 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 93 mm (3.7 inches) of precipitation spread over approximately 9 days.
JanFebMarAprMayJunJulAugSepOctNovDec57649711416215910474941325450
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
Choose your preferred precipitation unit

September Humidity in Princeton

In Princeton in September, humidity is 80%. With an average temperature of 20°C (69°F), this humidity feels like a warm blanket enveloping you, making every step slightly more challenging as you navigate the air that clings to your skin, often leaving you longing for a cool breeze while exploring the sights.

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 80%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec82%83%84%85%79%82%80%81%80%82%88%84%
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.
JanFebMarAprMayJunJulAugSepOctNovDec35689111098642
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.
 TemperaturePrecipitationHumidityUV
January Weather-4°C (25°F)57 mm (2.3 inches)82%moderate
February Weather-3°C (28°F)64 mm (2.5 inches)83%moderate
March Weather5°C (41°F)97 mm (3.8 inches)84%high
April Weather10°C (50°F)114 mm (4.5 inches)85%very high
May Weather17°C (63°F)162 mm (6.4 inches)79%very high
June Weather23°C (73°F)159 mm (6.2 inches)82%extreme
July Weather25°C (76°F)104 mm (4.1 inches)80%very high
August Weather23°C (74°F)74 mm (2.9 inches)81%very high
September Weather20°C (69°F)93 mm (3.7 inches)80%very high
October Weather13°C (55°F)132 mm (5.2 inches)82%high
November Weather4°C (39°F)54 mm (2.1 inches)88%moderate
December Weather1°C (33°F)50 mm (2.0 inches)84%low

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