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September Weather in South San Francisco, United States

Last updated: June 24, 2025

In September, the average temperature in South San Francisco, United States hovers around 17°C (63°F). You'll experience a minimum temperature of 11°C (51°F), while the mercury can soar to a maximum of 35°C (96°F). Expect minimal precipitation, with just 2 mm (0.1 in) over 0 days. The atmosphere is quite humid, featuring an average humidity level of 86%.

September Temperature in South San Francisco

In September in South San Francisco, the average temperature is 17°C (63°F). Maximum can reach 35°C (96°F) and minimum can be as low as 11°C (51°F). This makes South San Francisco an ideal destination for travelers seeking a pleasant climate with a mix of warm days and cooler nights.

September Weather in South San Francisco: Daily Temperature Highs, Lows, and Averages

The chart illustrates September temperature patterns in South San Francisco, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In South San Francisco, September typically has an average temperature of 17°C (63°F), with highs reaching up to 35°C (96°F) and lows dropping to around 11°C (51°F).
JanFebMarAprMayJunJulAugSepOctNovDec515253555659596162605552
Data source: Temperature data for South San Francisco 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 South San Francisco

In South San Francisco in September, the precipitation amount is 2 mm (0.1 in) during a span of 0 days.

September Precipitation Trends in South San Francisco

The chart displays monthly precipitation patterns in South San Francisco, 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 South San Francisco, September typically receives around 2 mm (0.1 inches) of precipitation spread over approximately 0 days.
JanFebMarAprMayJunJulAugSepOctNovDec1061097835203322305095
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
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September Humidity in South San Francisco

In South San Francisco in September humidity is 86%. With an average temperature of 17°C (63°F), this humidity feels like a heavy blanket wrapping around you, making the air feel thick and slightly stifling for traveling, as every step requires more effort and even a gentle breeze feels refreshing amidst the muggy atmosphere.

September Average Humidity in South San Francisco

This chart illustrates the average monthly humidity levels in South San Francisco, 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 South San Francisco is approximately 86%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec85%82%82%79%83%84%87%87%86%80%79%79%
Data source: Humidity data for September generated using information from the Copernicus Climate Change Service.

September UV Index in South San Francisco

In South San Francisco 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 South San Francisco.

Maximum UV Index Levels in South San Francisco for September

The chart shows the monthly maximum UV Index (UVI) for South San Francisco 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 South San Francisco typically reaches 9, which falls under the very high exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec3589101111109743
Data source: South San Francisco 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 South San Francisco Compares to Other Months

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

This table compares monthly weather conditions in South San Francisco, showing how September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
 TemperaturePrecipitationHumidityUV
January Weather11°C (52°F)106 mm (4.2 inches)85%moderate
February Weather11°C (52°F)109 mm (4.3 inches)82%moderate
March Weather12°C (53°F)78 mm (3.1 inches)82%very high
April Weather13°C (55°F)35 mm (1.4 inches)79%very high
May Weather14°C (57°F)20 mm (0.8 inches)83%very high
June Weather15°C (60°F)3 mm (0.1 inches)84%extreme
July Weather15°C (60°F)3 mm (0.1 inches)87%extreme
August Weather16°C (61°F)2 mm (0.1 inches)87%very high
September Weather17°C (63°F)2 mm (0.1 inches)86%very high
October Weather16°C (60°F)30 mm (1.2 inches)80%high
November Weather13°C (56°F)50 mm (2.0 inches)79%moderate
December Weather11°C (52°F)95 mm (3.7 inches)79%moderate

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