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September Weather in San Diego, United States

Last updated: June 24, 2025

In September, the average temperature in San Diego, United States hovers around 28°C (82°F), with minimums dipping to 15°C (60°F) and maximums soaring up to 40°C (104°F). Expect around 104 mm (4.1 in) of precipitation spread across 13 days. Additionally, the average humidity reaches a comfortable 73%, making it a perfect time to explore!

September Temperature in San Diego

In September in San Diego, the average temperature is 28°C (82°F), with maximums reaching up to 40°C (104°F) and minimums dropping as low as 15°C (60°F). This climate makes San Diego an ideal destination for travelers seeking warm weather and plenty of sunshine.

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

The chart illustrates September temperature patterns in San Diego, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In San Diego, September typically has an average temperature of 28°C (82°F), with highs reaching up to 40°C (104°F) and lows dropping to around 15°C (60°F).
JanFebMarAprMayJunJulAugSepOctNovDec586169748184858682756661
Data source: Temperature data for San Diego 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 San Diego

In San Diego in September, the precipitation amount is 104 mm (4.1 in) over the course of 13 days.

September Precipitation Trends in San Diego

The chart displays monthly precipitation patterns in San Diego, 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 San Diego, September typically receives around 104 mm (4.1 inches) of precipitation spread over approximately 13 days.
JanFebMarAprMayJunJulAugSepOctNovDec2724544199887952104443738
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
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September Humidity in San Diego

In San Diego in September humidity is 73%. With an average temperature of 28°C (82°F), this humidity feels like stepping into a warm, thick blanket, making traveling feel sticky and heavier; staying hydrated and taking breaks in the shade becomes essential.

September Average Humidity in San Diego

This chart illustrates the average monthly humidity levels in San Diego, 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 San Diego is approximately 73%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec83%79%76%77%80%73%66%65%73%76%80%86%
Data source: Humidity data for September generated using information from the Copernicus Climate Change Service.

September UV Index in San Diego

In San Diego in September, the maximum UV index reaches 11, which corresponds to an extreme Exposure Category. With a time to burn of just 10 minutes, it's essential to take precautions. For more details, you can check the Hourly UV Index in San Diego.

Maximum UV Index Levels in San Diego for September

The chart shows the monthly maximum UV Index (UVI) for San Diego 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 San Diego typically reaches 11, which falls under the extreme exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec6810111112121211975
Data source: San Diego 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 San Diego Compares to Other Months

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

This table compares monthly weather conditions in San Diego, showing how September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
 TemperaturePrecipitationHumidityUV
January Weather14°C (58°F)27 mm (1.1 inches)83%high
February Weather16°C (61°F)24 mm (1.0 inches)79%very high
March Weather21°C (69°F)54 mm (2.1 inches)76%very high
April Weather24°C (75°F)41 mm (1.6 inches)77%extreme
May Weather27°C (81°F)99 mm (3.9 inches)80%extreme
June Weather29°C (84°F)88 mm (3.4 inches)73%extreme
July Weather30°C (86°F)79 mm (3.1 inches)66%extreme
August Weather30°C (87°F)52 mm (2.1 inches)65%extreme
September Weather28°C (82°F)104 mm (4.1 inches)73%extreme
October Weather24°C (76°F)44 mm (1.7 inches)76%very high
November Weather19°C (66°F)37 mm (1.4 inches)80%high
December Weather16°C (61°F)38 mm (1.5 inches)86%moderate

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