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September Weather in Princeton, United States

Last updated: June 24, 2025

In Princeton, United States, the average temperature in September hovers around 18°C (64°F), making it a pleasant time to visit. Expect minimum temperatures to dip to 1°C (35°F), while daytime highs can reach up to 33°C (91°F). During this month, you can anticipate 89 mm (3.5 in) of precipitation spread over about 10 days, contributing to an average humidity level of 79%.

September Temperature in Princeton

In September in Princeton, the average temperature is 18°C (64°F). Maximums can reach 33°C (91°F), and minimums can be as low as 1°C (35°F). Travelers should be prepared for a range of temperatures and pack accordingly for both warm days and cooler 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 18°C (64°F), with highs reaching up to 33°C (91°F) and lows dropping to around 1°C (35°F).
JanFebMarAprMayJunJulAugSepOctNovDec202134445869747064503628
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 89 mm (3.5 in) over a period 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 89 mm (3.5 inches) of precipitation spread over approximately 10 days.
JanFebMarAprMayJunJulAugSepOctNovDec46506099117108109100891054648
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 79%. With an average temperature of 18°C (64°F), this humidity feels like a warm, sticky embrace that can make outdoor activities more challenging but also creates a lush, vibrant atmosphere that's perfect for exploring local culture and scenery.

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 79%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec85%85%85%85%78%80%78%76%79%83%88%82%
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 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 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 7, which falls under the high exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec34589101097532
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-7°C (20°F)46 mm (1.8 inches)85%moderate
February Weather-6°C (21°F)50 mm (2.0 inches)85%moderate
March Weather1°C (34°F)60 mm (2.4 inches)85%moderate
April Weather7°C (45°F)99 mm (3.9 inches)85%very high
May Weather15°C (59°F)117 mm (4.6 inches)78%very high
June Weather21°C (70°F)108 mm (4.3 inches)80%very high
July Weather23°C (74°F)109 mm (4.3 inches)78%very high
August Weather21°C (71°F)100 mm (3.9 inches)76%very high
September Weather18°C (64°F)89 mm (3.5 inches)79%high
October Weather10°C (51°F)105 mm (4.1 inches)83%moderate
November Weather2°C (36°F)46 mm (1.8 inches)88%moderate
December Weather-2°C (28°F)48 mm (1.9 inches)81%low

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