Last updated: August 31, 2025
September in Isabela, Puerto Rico showcases a tropical climate characterized by warm temperatures and significant rainfall. Daily highs reach a maximum of 31°C (88°F), while the average temperature lingers around 27°C (81°F). Nighttime brings cooler comfort with lows dipping to 25°C (77°F). This month is also marked by frequent showers, with total precipitation measuring 188 mm (7.4 in) across approximately 23 rainy days, contributing to the region's lush landscapes. The air remains humid, averaging 79%, creating a vibrant yet cozy atmosphere for both visitors and locals alike.
In September, Isabela, Puerto Rico, experiences a warm tropical climate, with temperatures ranging from a minimum of 25°C (77°F) to a maximum of 31°C (88°F). The month maintains an average temperature of 27°C (81°F), mirroring the warmth of the preceding summer months. This slight uptick in nighttime lows signals the transition toward fall while still embracing the lingering warmth of summer. As the highest temperatures remain consistent with August's peak, visitors can expect sunny days perfect for beach activities, although it's wise to be prepared for occasional rain showers typical of the season.
In September, Isabela, Puerto Rico experiences a significant uptick in rainfall, with an impressive 188 mm (7.4 in) accumulating over 23 days—the highest monthly total of the year. This marked increase underscores a transition from the drier summer months, particularly August, where rainfall also peaks at 97 mm (3.8 in), but across fewer days. The trend reveals that as the island heads deeper into the wet season, the frequency and intensity of precipitation intensify, setting the stage for lush landscapes while highlighting the region's vulnerability to tropical weather patterns. This pattern of increased moisture not only rejuvenates the delicate ecosystems but also brings the vibrant colors of nature to life, making September a month of transformation in Isabela's climate.
In September, Isabela, Puerto Rico experiences a notable humidity level of 79%, which marks a slight decline from the peak 80% recorded in the preceding months of July and August. This time of year reflects the tail end of the summer, where humidity typically remains high due to the Caribbean climate. Interestingly, the humidity levels during September remain consistent with the overall trend observed in late summer, fluctuating only modestly between 77% and 80% from June through August. As the year transitions into fall, October shows a slight decrease at 78%, suggesting a gradual shift toward drier conditions. Overall, September serves as a bridge between the sultry summer months and the cooler, slightly drier autumn, with humidity levels that are still comfortably humid, characteristic of Puerto Rico's tropical environment.
In September, the UV Index in Isabela, Puerto Rico remains consistently high at 13, categorizing it as extreme. This trend is part of an extended stretch of strong UV exposure from February to October, where values frequently peak at 13 or higher, requiring just 10 minutes of sun exposure before potential burns occur. As summer transitions into fall, residents and visitors alike are advised to remain vigilant against sun damage while enjoying the beautiful beaches and outdoor activities the region has to offer. For more detailed insights, check out the Isabela UV Index.
UV Risk Categories
In September, Isabela, Puerto Rico, enjoys a generous 316 hours of sunshine, continuing the warm summer trend. This month marks a slight dip from the peak sunlight hours of May and July, which each bask in 361 hours. However, it still shines brightly compared to the winter months, like January with just 261 hours and November at 298 hours. As summer fades into autumn, the sunny days of September serve as a gentle reminder of the tropical paradise that Isabela represents, offering plenty of opportunities to soak up the sun before the cooler months set in.
In Isabela, Puerto Rico, the likelihood of sunny weather in September stands at 53%, closely mirroring the sunshine chances of both April and October. This month marks a slight improvement from the summer's lower probabilities, which hover around the mid-40s in July and August. As we transition into autumn, the return to more favorable weather is evident, enhancing outdoor activities and enjoyment of the island's vibrant landscapes. With an increase in sunshine following the typically wetter summer months, September presents a balanced opportunity for sun-seekers and nature enthusiasts alike.
In September, daylight hours in Isabela, Puerto Rico, settle at a pleasant 12 hours, maintaining a balance characteristic of the preceding summer months. This trend showcases a gradual transition from the long, sun-filled days of June and July, which boast 13 hours of daylight, to the shorter days that begin in October. As the island moves from the peak summer season into autumn, the consistency of 12 hours in both September and August highlights the tropical rhythm of changing seasons, where the variations in daylight remain subtle yet significant. This gentle shift signifies the approach of the cooler months, as daylight gradually begins to wane toward the end of the year.
In September, the winds in Isabela, Puerto Rico, tend to calm down, with an average speed of only 3.7 m/s (8 mph), marking a noticeable dip from the summer months. This gentle breeze, the softest of the year, contrasts with the breezy highs of early summer, where speeds hovered around 5.3 m/s (12 mph). As the month transitions into October, the winds barely shift, settling at 3.5 m/s (8 mph), indicating a trend of diminishing gusts as the region approaches the heart of the hurricane season. While September invites a serene atmosphere, it also hints at an impending shift in weather patterns, as the island readies itself for the more turbulent winds that often accompany later autumn months.
Weather in Isabela varies notably across the year, with each month offering distinct climate conditions. This page compares September’s weather to other months in Isabela, focusing on differences in temperature, rainfall, humidity, and UV levels.
September and January present distinctly different weather patterns. In September, temperatures peak higher, with averages around 27°C (81°F) and maximums reaching 31°C (88°F). It is also a wetter month, experiencing about 188 mm (7.4 in) of rain over 23 days, resulting in high humidity levels of 79%. In contrast, January is cooler and drier, with average temperatures of 25°C (77°F) and maximums of 29°C (84°F). Precipitation significantly decreases to 34 mm (1.3 in) across just 11 days, maintaining a slightly lower humidity of 76%. For more details on January weather, visit Isabela weather in January.
September and February present contrasting weather experiences. In September, temperatures range from a minimum of 25°C (77°F) to a maximum of 31°C (88°F), with an average of 27°C (81°F). This month is notably humid, with 79% humidity and significant precipitation, totaling 188 mm (7.4 in) over 23 days. In contrast, February offers milder conditions, with minimum temperatures of 21°C (69°F) and a maximum of 30°C (86°F), averaging 25°C (76°F). The month is much drier, with only 39 mm (1.5 in) of rain over 13 days, and slightly lower humidity at 75%. For more details, you can visit Isabela weather in February.
In comparing the weather of September and March, September tends to be warmer, with average temperatures ranging from a minimum of 25°C (77°F) to a maximum of 31°C (88°F), while March displays slightly cooler temperatures, averaging between 21°C (70°F) and 29°C (84°F). Additionally, September experiences significantly higher precipitation, totaling 188 mm (7.4 in) over 23 days, compared to March, which sees only 72 mm (2.8 in) over 17 days. Humidity levels are also slightly higher in September at 79%, compared to March's 74%. For more detailed information on the weather in Isabela during March, you can visit Isabela weather in March.
When comparing the weather in September and April, September tends to be warmer and more humid. The average temperature in September hovers around 27°C (81°F), with a minimum of 25°C (77°F) and a maximum of 31°C (88°F). In contrast, April's temperatures are slightly cooler, averaging 25°C (78°F) with a minimum of 22°C (72°F) and a maximum of 30°C (86°F). Additionally, September is much wetter, receiving 188 mm (7.4 in) of precipitation over 23 days, compared to April's more moderate 66 mm (2.6 in) over 14 days. The humidity is also higher in September, at 79%, compared to April's 75%. For more detailed information on this month’s weather, visit Isabela weather in April.
When comparing the weather in September and May, both months feature high temperatures with a maximum of 31°C (88°F). However, September tends to be slightly warmer overall, with average temperatures of 27°C (81°F) versus May's average of 26°C (79°F). Precipitation in September is considerably higher at 188 mm (7.4 in) spread across 23 days, while May sees only 97 mm (3.8 in) of rain over 19 days. Additionally, September has a higher humidity level at 79%, compared to May’s 75%. For more details on Isabela's weather in May, visit Isabela weather in May.
In comparing September and June weather, both months exhibit similar temperature ranges, with daily minimums around 24-25°C (76-77°F), average temperatures of 27°C (81°F), and maximums reaching up to 31°C (88°F). However, September is notably wetter, receiving 188 mm (7.4 in) of precipitation over 23 days, compared to June's 85 mm (3.3 in) over 17 days. Additionally, September has a slightly higher humidity level at 79%, while June's humidity is at 77%. For a detailed overview of June weather in Isabela, you can refer to Isabela weather in June.
When comparing the weather in September and July, we find that both months exhibit similar average temperatures, hovering around 27°C (81°F) with maximums reaching up to 31°C (88°F). However, September tends to be noticeably wetter, receiving 188 mm (7.4 in) of precipitation over 23 days, compared to July's 91 mm (3.6 in) across 18 days. Additionally, while humidity levels are quite similar, September's average humidity is slightly lower at 79% versus July's 80%. For more detailed information about the July climate, you can visit Isabela weather in July.
In comparing the weather of September and August, we see that September is slightly warmer, with average temperatures around 27°C (81°F) and a maximum of 31°C (88°F), while August reaches a slightly higher maximum of 32°C (89°F) but has the same average temperature. Precipitation in September is significantly higher at 188 mm (7.4 in) over 23 days, contrasting with August's 97 mm (3.8 in) over 20 days. Humidity levels are comparable, with September at 79% and August slightly higher at 80%. For more detailed insights on August weather, you can visit Isabela weather in August.
September and October share similar temperature ranges, with September having a minimum of 25°C (77°F) and October slightly lower at 24°C (76°F). Both months average around 27°C (81°F) and peak at 31°C (88°F). However, October experiences a significant drop in precipitation, with 127 mm (5.0 in) over 21 days compared to September's 188 mm (7.4 in) over 23 days. Humidity levels remain quite close, with September at 79% and October slightly lower at 78%. For more detailed information, you can check Isabela weather in October.
September and November present contrasting weather patterns. In September, temperatures are generally warmer, with average highs reaching 31°C (88°F) and notable humidity levels at 79%. The month also experiences significant rainfall, totaling 188 mm (7.4 in) over 23 days. In comparison, November features slightly cooler temperatures, with averages around 26°C (79°F), and the maximum temperature peaking at 30°C (85°F). Additionally, November sees a decrease in precipitation, with only 99 mm (3.9 in) across 19 days, while maintaining similar humidity at 78%. For more details on November weather, you can visit Isabela weather in November.
September and December weather present a notable contrast in temperature and precipitation. In September, temperatures range from a minimum of 25°C (77°F) to a maximum of 31°C (88°F), with an average of 27°C (81°F). The month experiences significant rainfall, totaling 188 mm (7.4 in) across 23 days, contributing to a high humidity level of 79%. In contrast, December sees slightly cooler temperatures, with a minimum of 23°C (73°F) and a maximum of 30°C (86°F), averaging 25°C (78°F). Rainfall drops dramatically to 43 mm (1.7 in) over 15 days, resulting in a humidity level of 76%. For more details on December weather, you can visit Isabela weather in December.
As September unfolds in Isabela, the weather takes on a distinctive character compared to other months. With average temperatures hovering around 27°C (81°F), the warmth is palpable, yet it’s accompanied by a notable increase in humidity and precipitation, resulting in approximately 23 rainy days throughout the month. This blend of warmth and moisture contributes to a lush, tropical ambiance, making September feel both vibrant and dynamic. Visitors and locals alike should be prepared for the occasional downpour, which adds a refreshing contrast to the balmy temperatures. For a more detailed understanding of how September fits into Isabela's climate throughout the year, explore Isabela Climate.