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September Weather in Palo Alto, United States

Last updated: June 24, 2025

In September, the average temperature in Palo Alto, United States hovers around 19°C (67°F). Expect a minimum of 3°C (37°F) and a maximum that can reach up to 32°C (90°F). Prepare for 117 mm (4.6 in) of precipitation spread over 9 days, with an average humidity of 66%.

September Temperature in Palo Alto

In September in Palo Alto, the average temperature is 19°C (67°F). Maximums can reach 32°C (90°F), while minimums can drop as low as 3°C (37°F). This temperature range makes Palo Alto a versatile destination for travelers, offering pleasant days and cool nights for a variety of activities.

September Weather in Palo Alto: Daily Temperature Highs, Lows, and Averages

The chart illustrates September temperature patterns in Palo Alto, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Palo Alto, September typically has an average temperature of 19°C (67°F), with highs reaching up to 32°C (90°F) and lows dropping to around 3°C (37°F).
JanFebMarAprMayJunJulAugSepOctNovDec303339506169757266564135
Data source: Temperature data for Palo Alto 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 Palo Alto

In Palo Alto in September, the total precipitation amount is 117 mm (4.6 in) spread over a period of 9 days.

September Precipitation Trends in Palo Alto

The chart displays monthly precipitation patterns in Palo Alto, 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 Palo Alto, September typically receives around 117 mm (4.6 inches) of precipitation spread over approximately 9 days.
JanFebMarAprMayJunJulAugSepOctNovDec74106961111331181631551171179993
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
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September Humidity in Palo Alto

In Palo Alto in September humidity is 66%. With an average temperature of 19°C (67°F), this humidity feels like a warm blanket wrapping around you, making it mildly uncomfortable for traveling, as you may find yourself needing to frequently stop for hydration and to seek shade from the sun.

September Average Humidity in Palo Alto

This chart illustrates the average monthly humidity levels in Palo Alto, 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 Palo Alto is approximately 66%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec87%85%85%83%75%74%65%62%66%79%87%85%
Data source: Humidity data for September generated using information from the Copernicus Climate Change Service.

September UV Index in Palo Alto

In Palo Alto 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 Palo Alto.

Maximum UV Index Levels in Palo Alto for September

The chart shows the monthly maximum UV Index (UVI) for Palo Alto 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 Palo Alto typically reaches 8, which falls under the very high exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec356910101098642
Data source: Palo Alto 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 Palo Alto Compares to Other Months

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

This table compares monthly weather conditions in Palo Alto, showing how September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
 TemperaturePrecipitationHumidityUV
January Weather-1°C (30°F)74 mm (2.9 inches)87%moderate
February Weather1°C (33°F)106 mm (4.2 inches)85%moderate
March Weather4°C (39°F)96 mm (3.8 inches)85%high
April Weather10°C (50°F)111 mm (4.4 inches)83%very high
May Weather16°C (61°F)133 mm (5.2 inches)75%very high
June Weather21°C (69°F)118 mm (4.6 inches)73%very high
July Weather24°C (75°F)163 mm (6.4 inches)65%very high
August Weather22°C (73°F)155 mm (6.1 inches)62%very high
September Weather19°C (67°F)117 mm (4.6 inches)66%very high
October Weather13°C (57°F)117 mm (4.6 inches)79%high
November Weather5°C (42°F)99 mm (3.9 inches)87%moderate
December Weather1°C (35°F)93 mm (3.7 inches)85%low

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