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September Weather in San Ysidro, United States

Last updated: June 24, 2025

In San Ysidro, United States, the average temperature in September hovers around 25°C (77°F), making it a pleasant time to visit. However, be prepared for variations, as temperatures can dip to a cool 9°C (49°F) or soar up to a sizzling 37°C (99°F). Expect 24 mm (0.9 in) of precipitation over about 4 days, with average humidity levels at a comfortable 70%.

September Temperature in San Ysidro

In September in San Ysidro, the average temperature is 25°C (77°F). Maximum temperatures can reach up to 37°C (99°F), while the minimum can dip as low as 9°C (49°F). This warm climate makes San Ysidro an ideal destination for travelers seeking sunny days and outdoor activities.

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

The chart illustrates September temperature patterns in San Ysidro, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In San Ysidro, September typically has an average temperature of 25°C (77°F), with highs reaching up to 37°C (99°F) and lows dropping to around 9°C (49°F).
JanFebMarAprMayJunJulAugSepOctNovDec455058677583838277665546
Data source: Temperature data for San Ysidro 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 Ysidro

In San Ysidro in September, the precipitation amount is 24 mm (0.9 in) over a period of 4 days.

September Precipitation Trends in San Ysidro

The chart displays monthly precipitation patterns in San Ysidro, 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 Ysidro, September typically receives around 24 mm (0.9 inches) of precipitation spread over approximately 4 days.
JanFebMarAprMayJunJulAugSepOctNovDec1315163422313324211313
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
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September Humidity in San Ysidro

In San Ysidro in September, humidity is 70%. With an average temperature of 25°C (77°F), this humidity feels like walking through a warm, moist blanket that clings to your skin, making every step feel heavier as you explore the sights and sounds of your destination.

September Average Humidity in San Ysidro

This chart illustrates the average monthly humidity levels in San Ysidro, 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 Ysidro is approximately 70%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec79%79%65%55%54%53%55%58%70%75%83%82%
Data source: Humidity data for September generated using information from the Copernicus Climate Change Service.

September UV Index in San Ysidro

In San Ysidro 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 Ysidro.

Maximum UV Index Levels in San Ysidro for September

The chart shows the monthly maximum UV Index (UVI) for San Ysidro 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 Ysidro typically reaches 11, which falls under the extreme exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec5710121213121211865
Data source: San Ysidro 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 Ysidro Compares to Other Months

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

This table compares monthly weather conditions in San Ysidro, showing how September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
 TemperaturePrecipitationHumidityUV
January Weather7°C (45°F)13 mm (0.5 inches)79%moderate
February Weather10°C (50°F)14 mm (0.6 inches)79%high
March Weather14°C (58°F)16 mm (0.6 inches)65%very high
April Weather20°C (67°F)3 mm (0.1 inches)55%extreme
May Weather24°C (75°F)4 mm (0.2 inches)54%extreme
June Weather28°C (84°F)22 mm (0.9 inches)53%extreme
July Weather29°C (84°F)31 mm (1.2 inches)55%extreme
August Weather28°C (83°F)33 mm (1.3 inches)57%extreme
September Weather25°C (77°F)24 mm (0.9 inches)70%extreme
October Weather19°C (66°F)21 mm (0.8 inches)75%very high
November Weather13°C (56°F)13 mm (0.5 inches)83%high
December Weather8°C (47°F)12 mm (0.5 inches)82%moderate

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