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September Weather in San Sebastian, Mexico

Last updated: August 27, 2025

In San Sebastian, Mexico, the average temperature for September hovers around 18°C (65°F). Expect lows of 7°C (45°F) and highs reaching 28°C (83°F). Rain is quite common, with 123 mm (4.8 in) of precipitation spread over 20 days. You'll experience a high level of comfort with average humidity at 82%. Plan accordingly!

September Temperature in San Sebastian

In September in San Sebastian, the average temperature is 18°C (65°F). The maximum can reach 28°C (83°F), while the minimum can drop as low as 7°C (45°F). This mild climate makes San Sebastian an ideal destination for outdoor exploration and city sightseeing during this time of year.

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

The chart illustrates September temperature patterns in San Sebastian, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In San Sebastian, September typically has an average temperature of 18°C (65°F), with highs reaching up to 28°C (83°F) and lows dropping to around 7°C (45°F).
JanFebMarAprMayJunJulAugSepOctNovDec586266697067666564636058
Data source: Temperature data for San Sebastian 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 Sebastian

In San Sebastian in September, the total precipitation amount reaches 123 mm (4.8 in) over the course of 20 days.

September Precipitation Trends in San Sebastian

The chart displays monthly precipitation patterns in San Sebastian, 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 Sebastian, September typically receives around 123 mm (4.8 inches) of precipitation spread over approximately 20 days.
JanFebMarAprMayJunJulAugSepOctNovDec4281524969311612356152
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
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September Humidity in San Sebastian

In San Sebastian in September, humidity is 82%. With an average temperature of 18°C (65°F), this humidity feels like a warm, sticky embrace that can quickly leave travelers feeling fatigued and in need of frequent breaks to stay refreshed and hydrated.

September Average Humidity in San Sebastian

This chart illustrates the average monthly humidity levels in San Sebastian, 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 Sebastian is approximately 82%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec84%78%75%71%77%76%68%70%82%91%89%88%
Data source: Humidity data for September generated using information from the Copernicus Climate Change Service.

September UV Index in San Sebastian

In San Sebastian in September, the maximum UV index is 14, which corresponds to an extreme Exposure Category. The time to burn is just 10 minutes, so it's crucial to take precautions. For the detailed hourly UV index in San Sebastian, you can check here.

Maximum UV Index Levels in San Sebastian for September

The chart shows the monthly maximum UV Index (UVI) for San Sebastian 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 Sebastian typically reaches 14, which falls under the extreme exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec10121415151414131412108
Data source: San Sebastian 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 Sebastian Compares to Other Months

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

This table compares monthly weather conditions in San Sebastian, showing how September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
 TemperaturePrecipitationHumidityUV
January Weather14°C (58°F)4 mm (0.2 inches)84%very high
February Weather17°C (62°F)2 mm (0.1 inches)78%extreme
March Weather19°C (66°F)8 mm (0.3 inches)75%extreme
April Weather20°C (69°F)15 mm (0.6 inches)70%extreme
May Weather21°C (70°F)24 mm (0.9 inches)77%extreme
June Weather20°C (68°F)96 mm (3.8 inches)76%extreme
July Weather19°C (66°F)93 mm (3.7 inches)68%extreme
August Weather19°C (66°F)116 mm (4.6 inches)70%extreme
September Weather18°C (65°F)123 mm (4.8 inches)82%extreme
October Weather17°C (63°F)56 mm (2.2 inches)91%extreme
November Weather16°C (60°F)15 mm (0.6 inches)89%very high
December Weather15°C (59°F)2 mm (0.1 inches)88%very high

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