Last updated: February 24, 2025
September in Key Biscayne, United States, showcases a delightful tropical climate characterized by warm temperatures and frequent rainfall. With daily maximums reaching 33°C (91°F) and an average of 28°C (82°F), this month offers a balmy atmosphere perfect for outdoor activities. However, visitors should be prepared for high humidity levels at 76% and a significant precipitation total of 203 mm (8.0 in), spread over 22 rainy days, creating lush landscapes and vibrant scenery. Whether you seek sun-soaked days or refreshing showers, September in Key Biscayne promises a unique blend of weather to experience.
September marks a transitional phase in Key Biscayne, United States, where summer's warmth lingers just a bit longer. With minimum temperatures around 24°C (75°F), the nights remain pleasantly mild, while average daily highs reach up to 33°C (91°F), ensuring beachgoers can still bask in the sun. The consistent average temperature of 28°C (82°F) serves as a reminder of summer's charm, making it an ideal time for outdoor activities before the cooler fall days set in. As temperatures peak, they trend slightly downward towards autumn, yet September's balmy conditions encourage a vibrant atmosphere perfect for both relaxation and adventure.
September marks a significant peak in precipitation for Key Biscayne, as the month typically brings 203 mm (8.0 in) of rain, making it the wettest time of the year. This increase in rainfall coincides with the tail end of the summer, where the region experiences its highest number of rainy days, averaging 22 days. Following August's 181 mm (7.1 in), September intensifies the trend of summer storms, contributing to a lush landscape that prominently defines the area. While October sees a noticeable decrease to 157 mm (6.2 in), the wet conditions of September serve as a reminder of the tropical climate's seasonal variance. Overall, this month underscores the transition from the peak summer humidity into a drier autumn, illustrating the dynamic weather patterns that characterize Key Biscayne.
In Key Biscayne, September marks a notable point in the humidity cycle, maintaining an average of 76%. This aligns with a gradual increase from the summer months, where humidity dipped to its lowest at 69% in June. As summer transitions to fall, humidity begins to climb once more, peaking in late autumn months, with October and November seeing levels rise to 79% and 80% respectively. This upward trend emphasizes the subtropical climate's influence, where the air retains moisture, making evenings pleasantly warm yet often humid. The slight dip observed from August to September contrasts sharply with the consistent rise in the months that follow, highlighting the dynamic weather patterns characteristic of this coastal paradise.
In September, Key Biscayne experiences a UV Index of 11, placing it in the extreme exposure category with a burn time of just 10 minutes. This underscores a persistent trend of high UV levels that has characterized the summer months, with August and July also reflecting a peak UV Index of 12. Following a gradual increase from the moderately high levels in the earlier months of the year, September remains consistent with the preceding summer intensity, allowing little reprieve from the sun’s harsh rays. As the season shifts towards fall, a slight decline in the UV Index is anticipated in October, which is a reminder for locals and visitors alike to stay vigilant about sun protection. For more information, visit the Key Biscayne UV Index.
UV Risk Categories
September in Key Biscayne radiates with 314 hours of sunshine, offering a delightful transition from the summer heat to the refreshing fall. This month marks a slight dip from the peak of July and August, which enjoy 344 and 340 hours respectively, yet still presents a generous amount of sun for outdoor enthusiasts. As the days shorten and the humidity begins to ease, September invites visitors to relish in its golden light, setting the stage for stunning sunsets and vibrant beach days. This trend of plentiful sunshine continues into October, ensuring that while summer may be fading, the warmth and brightness linger on, making Key Biscayne a year-round paradise for sun-seekers.
As September rolls in, Key Biscayne experiences a noticeable dip in the likelihood of sunny weather, with a 31% chance of sunshine. This decrease is part of a broader trend observed throughout the summer months, where sunny days become increasingly rare, peaking in June and July at just 15% and 19% respectively. The transition from the sizzling summer to the more temperate fall months signals a gradual return to brighter skies, with October presenting a more favorable forecast at 44%. While September may not top the charts for sunshine, it offers a hint of improvement as the season shifts, paving the way for sunnier days ahead.
As summer gives way to fall, Key Biscayne experiences a smooth transition in daylight hours throughout September, maintaining 12 hours of sunlight each day. This trend follows the crest of summer, where the long days of 13 hours in June, July, and August gradually taper off. With September marking a near-equilibrium between light and dark, it signals the approaching shorter days of autumn, as daylight will dwindle further in the coming months. Interestingly, this gradual decrease from summer's peak highlights the consistent and predictable rhythm of daylight in this tropical paradise, enhancing the island's charm as it prepares for the cooler seasons ahead.
As September rolls in, Key Biscayne experiences a noticeable shift in its wind patterns, with average wind speeds dropping to a gentle 2.4 m/s (5 mph). This tranquil breeze marks a departure from the more robust winds of summer, where July and August recorded average speeds of 3.1 m/s (7 mph) and 3.4 m/s (8 mph) respectively. The calming winds of September invite a sense of serenity, setting the stage for the transition into autumn. As the year progresses, the wind picks up slightly again in October, but September’s soft whispers remind residents and visitors alike of the idyllic, laid-back charm that defines this coastal gem during the early fall.
The weather in Key Biscayne 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 Key Biscayne and find detailed weather information for every month.
September and January weather in Key Biscayne contrast significantly in terms of temperature and precipitation. September boasts a warm climate with average temperatures ranging from 24°C (75°F) to a peak of 33°C (91°F) and substantial rainfall of 203 mm (8.0 in) over 22 days, making it one of the wetter months of the year. In stark contrast, January features cooler temperatures, with a minimum of 7°C (44°F) and an average of 21°C (70°F), along with only 34 mm (1.3 in) of rainfall over just 6 days. The humidity remains relatively high in both months, at 76% in September and 81% in January, but the overall atmosphere feels much drier in the latter. For more details, check out Key Biscayne weather in January.
The weather in September is notably warmer and more humid compared to February. With temperatures ranging from a minimum of 24°C (75°F) to a maximum of 33°C (91°F) and an average of 28°C (82°F), September experiences a sultry climate that often results in heavy rainfall, accumulating around 203 mm (8.0 in) over approximately 22 days. In contrast, February offers a cooler respite, with temperatures ranging from a minimum of 10°C (51°F) to a maximum of 28°C (83°F) and an average of 23°C (73°F). This month sees much lower precipitation levels, at just 50 mm (2.0 in) over 9 days, and slightly higher humidity at 79%. For more detailed information, you can visit Key Biscayne weather in February.
In comparing the weather between September and March, there's a marked difference in temperatures and precipitation levels. September typically experiences warmer temperatures, with averages peaking at 28°C (82°F) and highs reaching 33°C (91°F). In contrast, March has a milder climate, with an average temperature of 23°C (73°F) and maximums around 30°C (86°F). Additionally, September is significantly wetter, accumulating 203 mm (8.0 in) of rainfall over 22 days, while March sees just 30 mm (1.2 in) of rain across only 5 days. Humidity remains consistent in both months at 76%, but the overall feel is vastly different due to the pronounced warmth and precipitation in September. For more details on the weather during this time, visit Key Biscayne weather in March.
When comparing the weather in September and April, notable differences emerge. September is generally warmer, with an average temperature of 28°C (82°F) and a maximum of 33°C (91°F), while April enjoys a cooler average of 25°C (77°F) and a maximum of 32°C (90°F). Additionally, September experiences significantly higher precipitation, totaling 203 mm (8.0 in) over 22 days, compared to April's 63 mm (2.5 in) over just 11 days. Humidity levels are relatively similar, with September at 76% and April slightly lower at 73%. For more detailed information, you can check Key Biscayne weather in April.
September weather tends to be hotter and more humid than that of May, with average temperatures reaching 28°C (82°F) compared to May's 26°C (79°F). The maximum temperature in September can climb up to 33°C (91°F), while May peaks at a slightly cooler 31°C (88°F). Additionally, September experiences significantly more rainfall, with 203 mm (8.0 in) of precipitation over 22 days, compared to May's 161 mm (6.3 in) over 18 days. The humidity is also higher in September at 76%, compared to 71% in May. For a more detailed look into May's weather patterns, check out Key Biscayne weather in May.
When comparing the weather in September and June, both months exhibit similar temperature ranges, with minimums around 24°C (75°F) and average highs of approximately 28°C (82°F). However, September tends to be slightly warmer with a maximum of 33°C (91°F) compared to June's peak of 32°C (90°F). Additionally, September experiences more rainfall, with 203 mm (8.0 in) over 22 days, while June sees about 172 mm (6.8 in) in the same number of days. Humidity is also higher in September at 76%, compared to June's 69%. For a detailed overview of June weather, you can check Key Biscayne weather in June.
In comparing the weather between September and July, we see that both months feature a similar temperature range, with minimums around 24°C (75°F), average highs of 28°C (82°F), and maximum temperatures reaching up to 33°C (91°F in September and 92°F in July). However, September experiences significantly more rainfall, with 203 mm (8.0 in) compared to July's 173 mm (6.8 in), and is characterized by more rainy days (22 compared to July's 26 days). Additionally, September has higher humidity levels at 76%, whereas July's humidity is slightly lower at 70%. This makes July feel slightly less oppressive despite the similar temperature ranges. For a detailed look at July weather specifics, visit Key Biscayne weather in July.
When comparing the weather in September to that in August, September tends to be slightly warmer at night with a minimum temperature of 24°C (75°F), compared to August's 25°C (76°F). The average temperature remains consistent at 28°C (82°F) for both months, while September offers a peak temperature of 33°C (91°F), slightly higher than August's maximum of 32°C (90°F). However, September sees more precipitation, with 203 mm (8.0 in) falling over 22 days, compared to 181 mm (7.1 in) over 25 days in August. Humidity is also higher in September at 76%, compared to 72% in August. For more details, you can check the Key Biscayne weather in August.
In September, temperatures are notably warmer, with minimums around 24°C (75°F) and maximums reaching 33°C (91°F), while October experiences cooler mornings with minimums dropping to 15°C (59°F). Both months see considerable precipitation, with September recording 203 mm (8.0 in) over 22 days, compared to October's 157 mm (6.2 in), despite having the same number of rainy days. Humidity remains high in both months, slightly increasing from 76% in September to 79% in October. For a closer look at the weather trends, check out Key Biscayne weather in October.
September and November exhibit notable differences in weather patterns. September tends to be warmer, with average temperatures around 28°C (82°F) and maximums reaching up to 33°C (91°F), while November sees cooler averages of 24°C (76°F) and maximums of 30°C (86°F). Additionally, September experiences significantly more rainfall, with 203 mm (8.0 in) over 22 days compared to November's 93 mm (3.7 in) over just 14 days. Humidity levels remain relatively high in both months, with September averaging 76% and November slightly higher at 80%. For more detailed insights, you can check out Key Biscayne weather in November.
September and December exhibit striking contrasts in weather patterns. September tends to be much warmer, with average temperatures around 28°C (82°F) and maximums peaking at 33°C (91°F). In contrast, December experiences cooler conditions, with an average temperature of 22°C (72°F) and highs reaching only 29°C (84°F). Additionally, September is notably wetter, boasting 203 mm (8.0 in) of precipitation over 22 days, while December features a much drier climate with only 41 mm (1.6 in) of rainfall spread over just 9 days. Humidity levels are relatively high in both months, with September at 76% and December slightly higher at 81%. For more details on December weather, visit Key Biscayne weather in December.
September in Key Biscayne serves as a bridge between the sultry summer months and the cooler fall ahead. With high humidity levels and frequent rainy days, the weather creates a lush, tropical atmosphere that is distinct from the drier months that follow. While temperatures remain warm and inviting, the notable increase in precipitation often brings a refreshing break from the heat, making this month feel more dynamic and lively. Travelers should embrace the unpredictable charm of September, as it showcases the island's vibrant character, inviting exploration amidst occasional showers. For further insights into what to expect throughout the year, check out Key Biscayne Climate.