Last updated: August 27, 2025
In September, San Francisco, Panama experiences a warm tropical climate characterized by a maximum temperature reaching 32°C (91°F) and an average temperature of 25°C (78°F). The nights offer a mild reprieve with temperatures dipping to a minimum of 21°C (70°F). Rainfall is significant during this month, with a staggering total of 459 mm (18.1 in) spread across 30 days, making it one of the wettest months of the year. The high humidity level at 87% adds to the tropical ambiance, creating an environment that is both lush and vibrant. Visitors should be prepared for frequent showers, but the lush greenery that results from this precipitation is truly a sight to behold.
In September, San Francisco's temperatures experience a gentle transition, with minimums around 21°C (70°F) and an average of 25°C (78°F), typically peaking at 32°C (91°F). This month marks a plateau in warmth, maintaining stable conditions similar to August, but with a slight decline in maximum temperatures. Overall, September showcases a consistent warmth that invites outdoor activities, though it's a touch milder than the peak of summer. As the city approaches fall, the weather remains inviting, making it an ideal time for exploring the vibrant streets of San Francisco or enjoying the beautiful coastal views.
In September, San Francisco, Panama experiences its peak rainfall, accumulating an impressive 459 mm (18.1 in) over the entire month, marking the highest monthly total in the year. The consistency of precipitation is evident, as rain falls on all 30 days, resulting in a backdrop of lush greenery throughout the region. Following the early year’s dry spell, where February and March see almost negligible rain, the wet season escalates dramatically in the late spring and summer months. This trend culminates in September's deluge, highlighting the transition to the heart of the rainy season where each day brings potential showers. The collective rain of late spring to early fall not only shapes the local climate but also enhances the biodiversity, making the environment vibrant and alive as it welcomes the soaking of autumn.
In September, San Francisco experiences a humidity level of 87%, consistent with the higher humidity trend observed during the summer months. After a gradual increase from 73% in May, humidity peaks in June and July at an impressive 90% and 88%, respectively, before showing a slight decline into August and September. This late-summer humidity, while lower than the peak months, still reflects a warm and humid climate as the city transitions into autumn. As the year progresses, a general trend emerges, with humidity gradually decreasing into the fall months, settling at 86% by October and November, further emphasizing the city’s unique maritime climate throughout the year.
In September, San Francisco, Panama, experiences a UV Index of 14, indicating an extreme exposure category, with a rapid burn time of just 10 minutes. This month mirrors the earlier summer trends, showcasing a slight dip from the peak index of 15 observed in May and April. However, the consistency of high UV levels throughout the months, particularly June to September, emphasizes the need for sun safety precautions. Whether you're basking in the sun or engaging in outdoor activities, always remember to protect your skin! For more on UV trends throughout the year, check out San Francisco UV Index.
UV Risk Categories
As September rolls into San Francisco, the city experiences a gentle decline in sunshine, with 217 hours illuminating the days—just a slight dip compared to the 207 hours of the preceding month. This gradual waning is part of a broader trend that sees summer's vibrant rays tapering off from a high of 335 hours in March. Interestingly, October glimpses a recovery with 224 hours of sunlight, hinting at a lingering warmth before the cooler months set in. Overall, the sunshine hours reflect a fascinating yearly rhythm, from the peak brightness of early spring to the cozy embraces of late autumn, beautifully illustrating San Francisco's unique climate tapestry.
When considering the likelihood of sunny weather in September in San Francisco, Panama, the data reveals a notably low chance of sun, at just 11%. This figure fits into a broader trend where summer months, particularly May through August, show a significant drop in sunny days, with some months dipping as low as 5%. Following September, there is a slight increase in sunlight potential with October at 15%. However, it's clear that the late summer and early autumn period offers limited opportunities for sunshine. Those looking for brighter skies might want to plan their visits outside of this timeframe to increase their chances of enjoying the sun.
In September, San Francisco enjoys a consistent 12 hours of daylight, mirroring the trend observed throughout the summer months from March to August. This stable daylight duration reflects the city's moderate climate and geographic positioning, offering residents ample opportunity to bask in the sun before the daylight begins to wane in October. As we transition into the cooler months, daylight drops to 11 hours in both October and continues through November and December, reminding us how rapidly seasons can shift. Meanwhile, in Panama, a tropical climate, the variation in daylight remains minimal year-round, typically providing about 12 hours of daylight even in September, ensuring that the allure of sun-soaked days continues uninterrupted. This consistency highlights the contrasting seasonal patterns between these two cities, evoking a sense of rhythm in nature's cycle.
In September, San Francisco experiences a notable dip in wind speed, averaging only 1.2 m/s (3 mph), which marks the lowest point in the annual cycle. This decrease follows a gradual rise from the calmest months of late spring and summer, peaking in March at 3.3 m/s (7 mph). As the year progresses, the winds typically gather strength through the early months, with January starting at 2.5 m/s (6 mph), yet by September, the persistent calm of summer lingers just a bit longer. Thereafter, October and November see a mild revival in wind speed, suggesting that while September might embody a tranquil stillness, the return of breezy days is just around the corner. Overall, the trend reflects a gentle ebb and flow, creating an inviting atmosphere for those drawn to the charming yet mellow winds of the region.
Weather in San Francisco varies notably across the year, with each month offering distinct climate conditions. This page compares September’s weather to other months in San Francisco, focusing on differences in temperature, rainfall, humidity, and UV levels.
In September, the weather is notably warmer and more humid, with average temperatures ranging from a minimum of 21°C (70°F) to a maximum of 32°C (91°F). This month experiences significant rainfall, with a total precipitation of 459 mm (18.1 in) over 30 days, leading to a high humidity level of 87%. In contrast, January offers milder conditions, featuring average temperatures from a minimum of 20°C (68°F) to a maximum of 33°C (91°F). The precipitation dramatically decreases, accumulating only 31 mm (1.2 in) over just 4 days, accompanied by a lower humidity of 72%. For more detailed insights, check out the San Francisco weather in January.
When comparing the weather in September and February, it is evident that September is characterized by a warmer, more humid climate. With average temperatures of 25°C (78°F), reaching a maximum of 32°C (91°F), and high humidity at 87%, September also sees significant precipitation, totaling 459 mm over 30 days. In contrast, February offers slightly cooler temperatures, with an average of 27°C (80°F) and a maximum of 34°C (94°F), yet experiences minimal rainfall of just 8 mm over 0 days, along with lower humidity at 71%. This stark difference makes February a drier and more comfortable month overall. You can check more details about San Francisco weather in February.
In comparing September and March weather, September tends to be more humid and wetter, with temperatures ranging from a minimum of 21°C (70°F) to a maximum of 32°C (91°F) and an impressive 459 mm (18.1 in) of precipitation spread over 30 days. In contrast, March features warmer average temperatures, with a range between 21°C (70°F) and 34°C (94°F), but it is significantly drier, receiving only 7 mm (0.3 in) of rain across zero rainy days. Additionally, the humidity level in September is much higher at 87%, whereas March enjoys a comparatively comfortable 69%. For a closer look at what to expect, check out San Francisco weather in March.
In comparing the weather between September and April, September experiences slightly lower average temperatures, ranging from a minimum of 21°C (70°F) to a maximum of 32°C (91°F), while April boasts warmer temperatures, with an average of 27°C (81°F) and a peak of 36°C (96°F). Additionally, September is characterized by significantly higher precipitation, totaling 459 mm (18.1 in) over 30 days, compared to April's much drier climate, with only 105 mm (4.1 in) over 12 days. Humidity levels are also notably higher in September at 87%, versus April's more comfortable 70%. For more details on the weather in April, you can visit San Francisco weather in April.
In comparing the weather between September and May, both months feature relatively warm temperatures, with September experiencing a minimum of 21°C (70°F) and an average of 25°C (78°F), while May offers slightly warmer conditions, peaking at an average of 26°C (79°F) and a maximum of 35°C (96°F). However, September tends to be much wetter, with a staggering 459 mm (18.1 in) of precipitation over 30 days, compared to May's 355 mm (14.0 in) over 27 days. Additionally, humidity levels are notably higher in September at 87%, versus a more comfortable 73% in May. For a more detailed look at the weather in May, you can check San Francisco weather in May.
September and June exhibit similar minimum temperatures, both starting at 21°C (70°F). However, June tends to be slightly warmer on average, with an average temperature of 26°C (78°F), compared to September's 25°C (78°F). In terms of maximum temperatures, June edges out with highs of 33°C (92°F), while September reaches a maximum of 32°C (91°F). Precipitation levels in September are significantly higher, with 459 mm (18.1 in) of rainfall over 30 days, compared to June's 353 mm (13.9 in) spread over 28 days. Humidity levels are also notably high in both months, with September at 87% and June at 90%. For more detailed information, you can check this link: San Francisco weather in June.
When comparing the weather in September and July, both months exhibit warm temperatures, with September having a slightly higher average temperature of 25°C (78°F) compared to July's 26°C (78°F). However, July typically experiences a higher maximum temperature of 33°C (92°F), while September peaks at 32°C (91°F). Precipitation is notably higher in September, with 459 mm (18.1 in) falling over 30 days compared to July's 404 mm (15.9 in) over 28 days. Humidity remains high in both months, with September at 87% and July at 88%. Overall, while July may be slightly warmer, September is characterized by increased precipitation. For more detailed information, you can visit San Francisco weather in July.
In comparing the weather of September to August, we see that both months experience similar temperature ranges, with September having a minimum of 21°C (70°F), an average of 25°C (78°F), and a maximum of 32°C (91°F). August, on the other hand, peaks slightly higher with a maximum of 33°C (91°F). Rainfall in September is notably higher, with 459 mm (18.1 in) over 30 days, compared to August's 359 mm (14.1 in) over 29 days. Humidity levels remain consistent at 87% for both months, indicating a persistently muggy atmosphere. For a detailed look at the weather specifics in August, you can refer to San Francisco weather in August.
September and October exhibit similar temperature ranges, with both months featuring a minimum of 21°C (70°F), an average of 25°C (78°F), and a maximum around 32°C (91°F for September and 90°F for October). However, October tends to be slightly drier, receiving 410 mm (16.2 in) of precipitation compared to September's 459 mm (18.1 in), while both months experience nearly the same number of rainy days—30 in September and 29 in October. Humidity levels are also quite similar, remaining high at 87% in September and slightly lower at 86% in October. For more detailed weather information, you can check San Francisco weather in October.
In September, temperatures range from a minimum of 21°C (70°F) to a maximum of 32°C (91°F), with an average of 25°C (78°F). The month is notably wet, recording a significant 459 mm (18.1 in) of precipitation over 30 days and high humidity at 87%. In contrast, November experiences similar temperature patterns, with a minimum of 21°C (70°F), an average of 25°C (77°F), and a maximum of 32°C (90°F). However, rainfall decreases to 385 mm (15.1 in) over 26 days, coupled with slightly lower humidity at 86%. For more details on the weather conditions, you can visit San Francisco weather in November.
In September, temperatures range from a minimum of 21°C (70°F) to a maximum of 32°C (91°F), with an average of 25°C (78°F). This month also sees a significant amount of rainfall, totaling 459 mm (18.1 in) over 30 days, contributing to high humidity levels at 87%. In contrast, December features slightly cooler temperatures, with a minimum of 20°C (69°F) and a similar maximum of 32°C (90°F), while maintaining an average of 26°C (78°F). Notably, December experiences much less precipitation at 103 mm (4.1 in) over just 9 days and lower humidity at 79%. For more details, check out San Francisco weather in December.
As summer transitions into autumn, September in San Francisco showcases a unique blend of warmth and moisture that sets it apart from other months. With average temperatures reaching a pleasant 25°C, this month often brings some of the year's warmest days, while the high humidity of 87% creates a muggy atmosphere. In contrast to the drier months of summer, September experiences substantial precipitation throughout its 30 days, leading to a remarkable 459 mm of rain. While the city is still basking in the sun, the increased wet weather prepares it for the cooler months ahead. For a deeper understanding of how San Francisco’s climate evolves throughout the year, explore more at San Francisco Climate.