September Weather in San Diego, United States

Last updated: February 24, 2025

In September, San Diego experiences delightful weather, with maximum temperatures reaching up to 31°C (88°F) and an average temperature of 21°C (70°F), making it an ideal time for outdoor activities. The minimum temperature hovers around 17°C (62°F), providing comfortable evenings. Remarkably, the month sees only 3 mm (0.1 in) of precipitation spread over zero rainy days, ensuring plenty of sunshine. With a humidity level of 52%, the climate remains pleasant and dry, perfect for enjoying the stunning coastal scenery and vibrant local events.

September Temperature in San Diego

In September, San Diego enjoys a delightful transition into early autumn, where temperatures reach a pleasant average of 21°C (70°F). With minimums around 17°C (62°F) and maximums peaking at 31°C (88°F), the city showcases a charming blend of warmth and comfort. This month marks a notable increase in warmth compared to the preceding summer, making it ideal for outdoor activities and beach outings. As the summer heat lingers, September remains a perfect time to experience the vibrant coastal lifestyle before the cooler months set in, highlighting its appeal as a year-round destination.

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.
JanFebMarAprMayJunJulAugSepOctNovDec575758616265697170686358
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

September in San Diego is characterized by its remarkably dry spell, with only 3 mm (0.1 in) of recorded precipitation, entirely absent of rain days. This minimal rainfall continues the trend set in the summer months, where July and August saw virtually no precipitation at all. As the region transitions into autumn, rainfall begins to gradually pick up, with October typically bringing a slight increase to 13 mm (0.5 in) over just two days. Overall, September serves as a bridge from the dry heat of summer to the onset of the wetter fall season, emphasizing San Diego's striking seasonal shifts in precipitation.

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.
JanFebMarAprMayJunJulAugSepOctNovDec45553820162114132460
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
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September Humidity in San Diego

As summer transitions into fall, September in San Diego brings a notable shift in humidity, averaging 52%. This figure marks a small increase from August's low of 42%, suggesting a gentle reintroduction of moisture into the coastal air. The humidity levels gradually rise from the summer's dry peak, which is observed from May through August when levels dip to their lowest. As the year progresses, humidity steadily escalates, reaching 58% in October and peaking at 77% in February. Overall, September serves as a transitional month where the refreshing coastal breezes begin to carry a hint of the wetter months ahead, signaling the end of summer's dry spell.

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, allowing you to see how September's humidity levels compare to other months.
JanFebMarAprMayJunJulAugSepOctNovDec72%77%67%56%46%48%46%42%52%58%66%74%
Data source: Humidity data for September generated using information from the Copernicus Climate Change Service.

September UV Index in San Diego

As September rolls into San Diego, residents and visitors should be prepared for very high UV Index levels, which persist at 10. This trend follows several months of extreme UV exposure, with May through August consistently marked by an index of 11. While the burn time remains relatively short at 15 minutes, it serves as a reminder that protective measures, such as sunscreen and hats, are essential even during this transition month. As we move into October, the UV index drops to a more manageable 7, indicating a return to high but less intense sun exposure. Staying informed about UV levels is crucial for enjoying the sunny San Diego weather safely—more details can be found at San Diego UV Index.

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.
JanFebMarAprMayJunJulAugSepOctNovDec468101111111010754
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.

September Sunshine in San Diego

As summer gracefully transitions into autumn, September in San Diego offers a delightful bounty of 318 hours of sunshine, maintaining a vibrant atmosphere for outdoor activities. This month marks a slight decline from the sun-drenched peak of July, which boasts 376 hours of brilliant rays. However, the warmth lingers, as September still outshines the earlier months of the year. From January's 195 hours to August’s 361 hours, there’s a clear upward trend in sunshine hours leading into September, showcasing the region's appeal to sun-seekers year-round. The consistent sunshine not only enhances the city's charm but also keeps summer's spirit alive just a little longer.

Monthly Sunshine Duration in San Diego: September Highlighted

The September sunshine duration represents the total number of hours San Diego experiences direct sunlight during the month of September, excluding cloudy or obstructed periods. This chart compares the sunshine duration of September with the other months of the year.
JanFebMarAprMayJunJulAugSepOctNovDec195h243h299h325h361h366h376h361h318h297h257h231h
Data source: San Diego September Sunshine duration data generated using information from the Copernicus Climate Change Service.

Chance of Sun in San Diego During September

September in San Diego typically boasts a 63% chance of sunny weather, aligning closely with the city's early months of the year—January, March, and even the preceding summer months like August. This consistency highlights a trend where the sun is a welcomed companion as summer transitions to fall. Interestingly, while the chances of sunshine dip in April and May, the likelihood remains relatively high from July to November, making September an ideal time for outdoor activities. With a slight increase in sunny prospects as the month nears its end, visitors can enjoy lingering summer days under the California sun before the cooler months set in.

Percentage of Sunny Days in September in San Diego

The chart illustrates the percentage of sunny days in San Diego throughout the year, with September highlighted. It highlights the variation in sunshine across each month and provides an overview of the typical frequency of sunny days, offering insights into how often San Diego experiences clear skies throughout the year.
JanFebMarAprMayJunJulAugSepOctNovDec63%62%63%50%42%47%56%60%63%64%63%47%
Data source: San Diego September chance of sun data, generated using information from the Copernicus Climate Change Service.

Daylight Hours in San Diego in September

As summer transitions into fall, September in San Diego offers a delightful balance of daylight, with the sun gracing the city for an average of 12 hours a day. This marks a gentle decline from the peak brightness of 14 hours seen in June and July, reflecting the gradual shift in seasons. Interestingly, this month retains a sense of warmth, as daylight hours start to taper off from the 13 hours enjoyed in the preceding August. With each passing day, residents begin to notice the subtle embrace of autumn, where the longer evenings invite cozy sunsets over the Pacific. As the days shorten, the rhythm of nature encourages a transition into the reflective vibes of the upcoming months.

Average Daylight Hours in San Diego for September

The chart illustrates the variation in daylight duration in San Diego throughout the year, with September highlighted. It shows the monthly changes in daylight hours, calculated by summing the hours between sunrise and sunset.
JanFebMarAprMayJunJulAugSepOctNovDec10h 15m11h 1m12h13h13h 50m14h 15m14h 1m13h 16m12h 19m11h 19m10h 27m10h 1m
Data source: San Diego daylight hours, calculated by summing the hours between sunrise and sunset for each day.

September Winds in San Diego

As summer transitions to fall, September in San Diego maintains a steady rhythm, with an average wind speed of 3.1 m/s (7 mph), mirroring the gentle breezes of the previous months. This consistent airflow is characteristic of the region, where winds hover around the same moderate level from June through September. Interestingly, the wind speeds begin to dip in October, suggesting a shift as the cooler months approach. The overall trend indicates that while San Diego enjoys pleasant winds throughout the summer, the gradual decline in speed hints at the impending change of seasons, creating a smooth bridge from the warm, sun-drenched days of summer to the crispness of autumn.

Average September Wind Speed in San Diego

The chart displays monthly wind speed patterns in San Diego, with values for each month shown alongside September's data, which is highlighted for easy comparison. It illustrates the average wind speed, offering insights into how September's wind conditions compare to the rest of the year.
JanFebMarAprMayJunJulAugSepOctNovDec3.02.73.43.23.13.33.13.13.1 m/s2.82.43.2
Data source: San Diego September wind data, generated using information from the Copernicus Climate Change Service.

How September Weather in San Diego Compares to Other Months

The weather in San Diego changes throughout the year, offering a unique experience in each season. Below is a month-by-month comparison of September's weather with other months, highlighting differences in temperature, precipitation, and other key factors. Click on each section to discover seasonal trends in San Diego and find detailed weather information for every month.

In September, San Diego enjoys warm temperatures with a minimum of 17°C (62°F) and an average of 21°C (70°F), peaking at a comfortable 31°C (88°F). The month typically experiences minimal precipitation of just 3 mm (0.1 in), with no rainy days and humidity levels at 52%. In contrast, January brings cooler conditions, with temperatures ranging from a minimum of 8°C (47°F) to an average of 14°C (58°F), and a maximum of 25°C (77°F). This month sees significantly more rain, with 45 mm (1.8 in) spread over approximately five days, accompanied by higher humidity levels at 72%. For more details on San Diego’s January weather, check out San Diego weather in January.

September and February present contrasting weather patterns. September enjoys warmer temperatures with a minimum of 17°C (62°F) and an average high of 31°C (88°F), making it a pleasant time with very little precipitation—just 3 mm (0.1 in) across the month. In contrast, February is much cooler, with temperatures ranging from a minimum of 7°C (45°F) to a maximum of 26°C (79°F). This month is also considerably wetter, with an average precipitation of 55 mm (2.2 in) spread over about 6 days, resulting in higher humidity levels at 77%. For more detailed information, you can check San Diego weather in February.

In September, the weather tends to be warm and dry, with temperatures ranging from a minimum of 17°C (62°F) to a maximum of 31°C (88°F) and an average of 21°C (70°F). With only 3 mm (0.1 in) of precipitation over the month and zero rainy days, the humidity remains relatively low at 52%. In contrast, March experiences cooler temperatures, with a minimum of 8°C (47°F) and a maximum of 26°C (80°F), averaging around 15°C (59°F). This month is also wetter, receiving 38 mm (1.5 in) of rainfall across eight days, and with higher humidity at 67%. For more detailed insights, you can check San Diego weather in March.

In September, the weather is warmer, with an average temperature of 21°C (70°F) and maximum highs reaching 31°C (88°F), while April features a cooler average temperature of 16°C (61°F) and maximums up to 29°C (84°F). September boasts a remarkably dry spell with only 3 mm of precipitation over no rainy days, whereas April experiences a bit more moisture, with 20 mm spread across two days. The humidity levels are slightly lower in September at 52%, compared to 56% in April, contributing to a more comfortable feel during the former month. For more specific information about the weather in April, you can check out San Diego weather in April.

September features warmer temperatures compared to May, with an average of 21°C (70°F) and maximums reaching up to 31°C (88°F). In contrast, May has a cooler average of 17°C (62°F) and a maximum of 25°C (78°F). Additionally, September is notably drier, experiencing no precipitation, whereas May sees an average rainfall of 16 mm (0.6 in) over four days. Humidity levels are slightly higher in September at 52%, compared to May's 46%. For more details, you can check San Diego weather in May.

In comparing the weather of September and June, September generally experiences warmer temperatures, with a minimum of 17°C (62°F) and an average of 21°C (70°F), compared to June's minimum of 14°C (58°F) and an average of 18°C (65°F). While both months have similar low precipitation levels—September at 3 mm (0.1 in) and June at 2 mm (0.1 in)—September tends to be slightly more humid, averaging 52% compared to June’s 48%. Overall, September offers a warmer and more humid climate than June. For more detailed information on June weather, you can check San Diego weather in June.

September and July in San Diego showcase mild temperatures and minimal precipitation, making both months quite pleasant. In September, the temperatures range from a minimum of 17°C (62°F) to a maximum of 31°C (88°F), with an average of 21°C (70°F) and a relative humidity of 52%. In contrast, July features slightly cooler temperatures, with a minimum of 16°C (62°F) and a maximum of 29°C (85°F), while maintaining the same average of 21°C (69°F) and a lower humidity of 46%. Both months experience negligible rainfall, with September receiving only 3 mm (0.1 in) and July slightly more at 1 mm (0.1 in). For more details on July's climate, check San Diego weather in July.

In September, temperatures show a slight variation compared to August, with both months having a minimum of 17°C (62°F). However, September enjoys warmer maximum temperatures, reaching up to 31°C (88°F), compared to August’s peak of 29°C (84°F). The average temperature remains quite similar between the two months, at 21°C (70°F) for September and 21°C (71°F) for August. Both months experience very little precipitation, though September has slightly lower rainfall at 3 mm (0.1 in) compared to August's 1 mm (0.0 in) and neither month recorded any rainy days. Additionally, September is slightly more humid at 52% compared to August's 42%. For more detailed statistics on August weather, check out San Diego weather in August.

September typically boasts warmer temperatures, with minimums around 17°C (62°F) and maximums reaching up to 31°C (88°F). The month is characterized by minimal precipitation, averaging just 3 mm (0.1 in) and no rainy days, resulting in a comfortable humidity level of 52%. In contrast, October sees slightly cooler temperatures with a minimum of 13°C (55°F) and an average of 20°C (68°F), although it can still peak at 32°C (90°F). This month experiences increased rainfall, with 13 mm (0.5 in) of precipitation over two days, leading to a higher humidity of 58%. For more details on October weather, check out San Diego weather in October.

In September, the weather is typically warmer, with temperatures ranging from a mild 17°C (62°F) at night to a high of 31°C (88°F) during the day, accompanied by low humidity at 52% and almost no precipitation. In contrast, November brings cooler temperatures, with a minimum of 10°C (51°F) and a maximum of 27°C (81°F), along with increased humidity at 66% and a noted rise in precipitation, totaling 24 mm (0.9 in) over two days. For more detailed insights into the climate during this month, you can check San Diego weather in November.

September and December present contrasting weather conditions. In September, temperatures range from a mild 17°C (62°F) at night to a warm 31°C (88°F) during the day, with very little precipitation and average humidity at 52%. In stark contrast, December sees cooler temperatures, with a minimum of 8°C (47°F) and a maximum of 24°C (76°F). This month experiences significantly higher precipitation of 60 mm (2.4 in) spread over approximately five rainy days, accompanied by increased humidity levels of 74%. For a more detailed look at December's climate, you can visit San Diego weather in December.

Compare San Diego's Climate with Cities Worldwide

Conclusion: What to Expect From September Weather in San Diego

As summer gradually transitions to autumn, September in San Diego offers a delightful reprieve from the intense heat of July and August. With pleasant average temperatures hovering around a comfortable 21°C (70°F) and maximums peaking at 31°C (88°F), visitors can enjoy outdoor activities in ideal conditions. Additionally, the month boasts clear skies and minimal precipitation, with absolutely no rain, contrasting sharply with the wetter winter months ahead. The humidity remains moderate at 52%, ensuring warm but enjoyable days without the oppressive stickiness often found elsewhere. For a deeper dive into the overall weather patterns that shape this vibrant city, explore the seasonal changes and climate nuances at San Diego Climate.