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September Weather in Millbrae, United States

Last updated: June 24, 2025

In September, the average temperature in Millbrae, United States is a pleasant 16°C (62°F), with a range that can dip to a minimum of 11°C (52°F) and soar to a maximum of 31°C (88°F). You'll find the climate relatively dry, with only 3 mm (0.1 in) of precipitation across 0 days. The air feels quite humid, averaging around 86%, making for a unique experience in this beautiful destination!

September Temperature in Millbrae

In September in Millbrae, the average temperature is 16°C (62°F). The maximum can reach 31°C (88°F), while the minimum can be as low as 11°C (52°F). This mild climate makes Millbrae an ideal destination for travelers seeking pleasant weather and outdoor adventures.

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

The chart illustrates September temperature patterns in Millbrae, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Millbrae, September typically has an average temperature of 16°C (62°F), with highs reaching up to 31°C (88°F) and lows dropping to around 11°C (52°F).
JanFebMarAprMayJunJulAugSepOctNovDec525253545558586062595653
Data source: Temperature data for Millbrae 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 Millbrae

In Millbrae in September, the precipitation amount is 3 mm (0.1 in) during a total of 0 days.

September Precipitation Trends in Millbrae

The chart displays monthly precipitation patterns in Millbrae, 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 Millbrae, September typically receives around 3 mm (0.1 inches) of precipitation spread over approximately 0 days.
JanFebMarAprMayJunJulAugSepOctNovDec1021017834224333274892
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
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September Humidity in Millbrae

In Millbrae in September humidity is 86%. With an average temperature of 16°C (62°F), this humidity feels like a muggy embrace that can make traveling slightly uncomfortable, as the stickiness clings to your skin and the air seems thick, enticing you to seek shade and refreshment more often.

September Average Humidity in Millbrae

This chart illustrates the average monthly humidity levels in Millbrae, 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 Millbrae 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 Millbrae

In Millbrae 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 Millbrae.

Maximum UV Index Levels in Millbrae for September

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

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

This table compares monthly weather conditions in Millbrae, showing how September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
 TemperaturePrecipitationHumidityUV
January Weather11°C (53°F)102 mm (4.0 inches)85%moderate
February Weather11°C (53°F)101 mm (4.0 inches)82%moderate
March Weather12°C (53°F)77 mm (3.0 inches)82%very high
April Weather12°C (55°F)34 mm (1.3 inches)79%very high
May Weather13°C (56°F)22 mm (0.9 inches)83%very high
June Weather15°C (58°F)4 mm (0.2 inches)84%extreme
July Weather15°C (59°F)3 mm (0.1 inches)87%extreme
August Weather16°C (61°F)3 mm (0.1 inches)87%very high
September Weather16°C (62°F)3 mm (0.1 inches)86%very high
October Weather15°C (60°F)27 mm (1.1 inches)80%high
November Weather13°C (56°F)48 mm (1.9 inches)79%moderate
December Weather12°C (53°F)92 mm (3.6 inches)79%moderate

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