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September Weather in Philadelphia, United States

Last updated: June 24, 2025

In September, the average temperature in Philadelphia, United States is a comfortable 25°C (77°F). However, temperatures can range from a chilly 11°C (52°F) to a sweltering 38°C (100°F). Expect 93 mm (3.7 in) of precipitation spread over 9 days, adding to an average humidity level of 74%. Stay prepared and enjoy the climate!

September Temperature in Philadelphia

In September in Philadelphia, the average temperature is 25°C (77°F). Maximums can reach 38°C (100°F), and minimums can be as low as 11°C (52°F). This comfortable climate makes Philadelphia an ideal destination for travelers seeking both warm days and cooler nights.

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

The chart illustrates September temperature patterns in Philadelphia, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Philadelphia, September typically has an average temperature of 25°C (77°F), with highs reaching up to 38°C (100°F) and lows dropping to around 11°C (52°F).
JanFebMarAprMayJunJulAugSepOctNovDec485360647378818077685451
Data source: Temperature data for Philadelphia 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 Philadelphia

In Philadelphia in September, the precipitation amount is 93 mm (3.7 in) over the course of 9 days.

September Precipitation Trends in Philadelphia

The chart displays monthly precipitation patterns in Philadelphia, 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 Philadelphia, September typically receives around 93 mm (3.7 inches) of precipitation spread over approximately 9 days.
JanFebMarAprMayJunJulAugSepOctNovDec1101731221581291681071309310668121
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
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September Humidity in Philadelphia

In Philadelphia in September humidity is 74%. With an average temperature of 25°C (77°F), this humidity feels like a warm, muggy blanket wrapping around you, making travel a bit more challenging as you find yourself sticky and in need of frequent breaks to hydrate and cool down.

September Average Humidity in Philadelphia

This chart illustrates the average monthly humidity levels in Philadelphia, 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 Philadelphia is approximately 74%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec85%84%82%82%82%79%82%77%74%73%85%88%
Data source: Humidity data for September generated using information from the Copernicus Climate Change Service.

September UV Index in Philadelphia

In Philadelphia in September, the maximum UV index is 9, which corresponds to a very high Exposure Category. The time to burn is just 15 minutes, so it's essential to take precautions. For detailed information, you can check the Hourly UV Index in Philadelphia.

Maximum UV Index Levels in Philadelphia for September

The chart shows the monthly maximum UV Index (UVI) for Philadelphia 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 Philadelphia typically reaches 9, which falls under the very high exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec47810111111119864
Data source: Philadelphia 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 Philadelphia Compares to Other Months

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

This table compares monthly weather conditions in Philadelphia, showing how September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
 TemperaturePrecipitationHumidityUV
January Weather9°C (48°F)110 mm (4.3 inches)85%moderate
February Weather11°C (53°F)173 mm (6.8 inches)84%high
March Weather15°C (60°F)121 mm (4.8 inches)82%very high
April Weather18°C (64°F)158 mm (6.2 inches)82%very high
May Weather23°C (73°F)129 mm (5.1 inches)82%extreme
June Weather26°C (79°F)168 mm (6.6 inches)79%extreme
July Weather27°C (81°F)107 mm (4.2 inches)82%extreme
August Weather27°C (80°F)130 mm (5.1 inches)77%extreme
September Weather25°C (77°F)93 mm (3.7 inches)74%very high
October Weather20°C (68°F)106 mm (4.2 inches)73%very high
November Weather12°C (54°F)68 mm (2.7 inches)85%high
December Weather10°C (51°F)121 mm (4.8 inches)88%moderate

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