September Weather in San Diego, Mexico

Last updated: August 27, 2025

In September, the average temperature in San Diego, Mexico hovers around 18°C (65°F). You'll experience a pleasant range, with minimums dipping to 10°C (50°F) and maximums reaching up to 27°C (81°F). However, keep an umbrella handy, as precipitation averages 339 mm (13.3 in) over 28 days, contributing to a high humidity level of 86%.

September Temperature in San Diego

In September in San Diego, the average temperature is 18°C (65°F), with maximums reaching up to 27°C (81°F) and minimums dropping as low as 10°C (50°F). This pleasant weather makes it an ideal time for outdoor activities and exploration.

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 18°C (65°F), with highs reaching up to 27°C (81°F) and lows dropping to around 10°C (50°F).

Data source: Temperature data for San Diego generated using information from the Copernicus Climate Change Service.

September Precipitation in San Diego

In San Diego in September, the total precipitation amount is 339 mm (13.3 in) spread over the course of 28 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 339 mm (13.3 inches) of precipitation spread over approximately 28 days.

Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.

Choose your preferred precipitation unit

Millimeters (mm) Inches (in)

September Humidity in San Diego

In San Diego in September humidity is 86%. With an average temperature of 18°C (65°F), this humidity feels like you’re wrapped in a warm, heavy blanket, making outdoor activities feel quite muggy and sticky for traveling.

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 86%, offering insight into how humid the weather typically is during this month.

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 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 Diego, you can check here.

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 14, which falls under the extreme exposure category.

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.
	Temperature	Precipitation	Humidity	UV
January Weather	13°C (55°F)	88 mm (3.5 inches)	88%	very high
February Weather	15°C (58°F)	64 mm (2.5 inches)	86%	extreme
March Weather	16°C (61°F)	93 mm (3.7 inches)	84%	extreme
April Weather	18°C (65°F)	133 mm (5.2 inches)	81%	extreme
May Weather	19°C (67°F)	190 mm (7.5 inches)	82%	extreme
June Weather	19°C (66°F)	262 mm (10.3 inches)	81%	extreme
July Weather	18°C (65°F)	210 mm (8.3 inches)	81%	extreme
August Weather	18°C (65°F)	291 mm (11.4 inches)	82%	extreme
September Weather	18°C (65°F)	339 mm (13.3 inches)	86%	extreme
October Weather	17°C (63°F)	217 mm (8.5 inches)	90%	extreme
November Weather	15°C (59°F)	111 mm (4.4 inches)	91%	very high
December Weather	13°C (57°F)	51 mm (2.0 inches)	91%	very high