Last updated: August 21, 2025
In Atenas, Costa Rica, September is characterized by a warm and humid climate, with average temperatures hovering around 23°C (74°F). Daily highs can reach a maximum of 29°C (85°F), while cool evenings drop to a comfortable minimum of 18°C (66°F). This month is notably wet, with a substantial precipitation total of 461 mm (18.2 in) over 29 rainy days, making it one of the wetter times of the year. The humidity level averages around 81%, creating a lush and vibrant atmosphere, ideal for experiencing the region's rich natural beauty.
In September, Atenas, Costa Rica, experiences mild temperatures that highlight the beautiful transition into the rainy season. The average temperature hovers around a comfortable 23°C (74°F), with minimums dipping to 18°C (66°F) and maximums reaching a pleasant 29°C (85°F). This month marks a slight cooling trend compared to the preceding summer months, where temperatures often peak above 30°C (86°F). The weather remains fairly consistent, showcasing Atenas' trademark blend of warmth and refreshment, making it an ideal time for visitors to enjoy the lush, vibrant landscape that flourishes during this season. With typical humidity and the frequent, gentle rain, September presents a unique charm that captures the essence of Costa Rica's lush beauty.
In September, Atenas, Costa Rica, experiences a significant surge in rainfall, with an impressive 461 mm (18.2 in) accumulating over 29 days. This marks one of the wettest months of the year, following the already high precipitation of August (393 mm). The transition from the drier months, such as January with only 28 mm, to this peak indicates a clear seasonal pattern, where the rains intensify as the country approaches the end of the rainy season. As we transition into October, a further increase in precipitation to 639 mm (25.2 in) suggests that the lush landscapes of Atenas thrive under these abundant showers, fostering vibrant flora and sustaining local agriculture.
In September, humidity in Atenas, Costa Rica, hovers around a significant 81%, contributing to the region's lush landscapes and vibrant ecosystems. This level marks a slight dip from the peak humidity experienced in the summer months of July and June, when figures soared to 85% and 84%, respectively. As the rainy season deepens, the humidity remains consistently high, indicative of the tropical climate's characteristic warmth and moisture. The trend observed throughout the year shows a gradual increase starting from the drier months of January through March, where levels dropped to around 66%. By the time September arrives, the humidity begins to stabilize before slightly decreasing in October and November, creating a transitional phase as the region heads towards the dryer months ahead.
In September, Atenas, Costa Rica, continues to experience an extreme UV Index of 13, maintaining a consistent trend observed throughout the year. This month falls into the same exposure category as August, where the UV Index was slightly higher at 13, just like in the preceding months from May to July. With a burn time of only 10 minutes, it's crucial for residents and visitors alike to take protective measures against the sun. This pattern highlights Atenas's persistent need for sun safety, standing out particularly in the dry season when UV levels peak. Stay informed and plan your outdoor activities wisely by checking the Atenas UV Index.
UV Risk Categories
As September unfolds in Atenas, Costa Rica, residents and visitors alike are treated to an inviting 230 hours of sunshine. This marks a slight dip from the peak sunshine of 329 hours in March, but it remains a delightful escape from the cloudier months of June and July, which saw only 226 and 209 hours, respectively. The sunny days in September signal the tail end of the dry season, blending into the vibrant rain-soaked months ahead. With the warm sun illuminating the picturesque landscapes, September offers a perfect blend of pleasant temperatures and invigorating outdoor adventures, making it an ideal time to explore the natural beauty of this tropical paradise.
In Atenas, Costa Rica, September is one of the months where you can expect the least chance of sunshine, with just a 10% likelihood of clear skies. This marks a significant drop from the earlier months, where the sun shines more frequently, peaking in January with a 57% chance. As the year transitions from the dry season to the wet season, June through August sees a decline in sunny days, reaching a low in September before beginning to recover slightly in October at 16%. While September's weather tends toward overcast skies and rain, it's essential for visitors to embrace the lush, vibrant atmosphere this month brings, knowing that sunnier days await just around the corner.
In Atenas, Costa Rica, September enjoys a generous 12 hours of daylight, a trend that persists through the country's central months from March to August. This consistent daylight duration allows locals and visitors alike to enjoy the vibrant landscapes, outdoor activities, and the rich biodiversity that the region has to offer. As the year progresses toward October, daylight begins to wane slightly, shifting back to 11 hours, but September stands out as a peak time for sun-soaked adventures. The reliable and extended daylight offers an ideal backdrop for experiencing the lush beauty and cultural richness of Atenas during the transitional phase of the rainy season.
In September, Atenas, Costa Rica experiences a gentle shift in its wind patterns, with an average wind speed of 1.2 m/s (3 mph). This slight increase from the earlier summer months reflects a subtle transition in the season, following the calmest winds of August. While September’s breezes are relatively mild, they contribute to the overall refreshing ambiance of the area, signaling the approach of the more variable winds of the upcoming months. As the year unfolds, Atenas typically sees a gradual increase in wind speeds from October through December, hinting at the invigorating rhythm of nature that characterizes this vibrant locale.
Weather in Atenas varies notably across the year, with each month offering distinct climate conditions. This page compares September’s weather to other months in Atenas, focusing on differences in temperature, rainfall, humidity, and UV levels.
In September, the weather tends to be warm and humid, with temperatures ranging from a minimum of 18°C (66°F) to a maximum of 29°C (85°F) and an average of 23°C (74°F). This month sees significant rainfall, with 461 mm (18.2 in) of precipitation spread across 29 days, resulting in a high humidity level of 81%. In contrast, January offers a more stable climate, with slightly cooler and drier conditions. The temperature ranges from a minimum of 17°C (63°F) to a maximum of 31°C (87°F), maintaining the same average of 23°C (74°F). Precipitation significantly decreases to just 28 mm (1.1 in) over 7 days, leading to a lower humidity level of 68%. For more details about January's weather, you can check this link: Atenas weather in January.
September and February present contrasting weather patterns. September features cooler temperatures, with averages ranging from a minimum of 18°C (66°F) to a maximum of 29°C (85°F), and is characterized by high humidity at 81%. It also experiences significant rainfall, with 461 mm (18.2 in) spread over 29 days. In contrast, February offers warmer temperatures, with a minimum of 16°C (62°F) and a maximum of 31°C (88°F), along with much lower precipitation of only 13 mm (0.5 in) across three days and a reduced humidity level of 68%. For a more detailed insight into February weather, check Atenas weather in February.
In September, the weather tends to be quite humid with an average temperature of 23°C (74°F) and frequent rainfall, totaling 461 mm (18.2 in) over 29 days. The high humidity level of 81% contributes to a muggy atmosphere, making it feel warmer than it actually is. In contrast, March offers a more comfortable climate, with temperatures ranging from a minimum of 18°C (64°F) to a maximum of 32°C (89°F) and an average temperature of 25°C (77°F). Precipitation drops significantly to just 18 mm (0.7 in) over 4 days, resulting in lower humidity at 66%. For a detailed look at the weather in March, you can check Atenas weather in March.
When comparing the weather in September and April, there are some notable differences. September experiences milder temperatures, with an average of 23°C (74°F) and maximums reaching 29°C (85°F), while April tends to be warmer on average at 24°C (76°F) and can peak at 31°C (89°F). However, September is considerably wetter, receiving about 461 mm (18.2 in) of precipitation over 29 days, compared to April's 118 mm (4.6 in) over 24 days. Additionally, September has a higher humidity level at 81%, whereas April's humidity is lower at 67%. For more details on April weather, you can check Atenas weather in April.
In comparing the weather of September and May, both months present warm temperatures, but with some notable differences. September has a minimum temperature of 18°C (66°F) and an average of 23°C (74°F), while May starts slightly warmer with a minimum of 19°C (67°F) and an average of 24°C (75°F). The maximum temperatures are similar, with September reaching 29°C (85°F) and May slightly warmer at 30°C (86°F).
Precipitation levels are relatively high in both months, but September sees a greater amount with 461 mm (18.2 in) over 29 days, compared to May's 412 mm (16.2 in) over 30 days. Humidity is also higher in September at 81%, contrasted with May's more comfortable 69%. For a more detailed look into May's climate, check out Atenas weather in May.
September and June present a similar tropical climate, with some notable differences in their weather patterns. In September, the minimum temperature hovers around 18°C (66°F), with an average of 23°C (74°F) and a maximum reaching 29°C (85°F). This month experiences higher precipitation, totaling 461 mm (18.2 in) over 29 days, and maintains a humidity level of 81%. In contrast, June's temperatures are slightly higher, with a minimum of 19°C (66°F), an average of 24°C (75°F), and a maximum of 30°C (86°F). While the rain is slightly less in June, at 397 mm (15.6 in) across 30 days, the humidity is relatively high at 84%. For more detailed information, you can check Atenas weather in June.
When comparing the weather in September to that of July, we see some notable differences. September tends to have slightly cooler temperatures, with a minimum of 18°C (66°F) and an average of 23°C (74°F), compared to July's minimum of 19°C (67°F) and average of 24°C (75°F). Both months experience similar maximum temperatures, peaking at 29°C (85°F). However, September is significantly wetter, receiving 461 mm (18.2 in) of precipitation over 29 days, whereas July has a total of 296 mm (11.7 in) spread over 30 days. Humidity levels are also comparable but slightly higher in July at 85%, compared to September's 81%. For more detailed information on the weather in July, you can visit Atenas weather in July.
In comparing the weather of September and August, we see subtle differences and similarities. Both months have a similar average temperature of 23°C (74°F), but September tends to have slightly cooler minimum and maximum temperatures, with lows of 18°C (66°F) compared to August's 19°C (66°F), and maximums reaching only 29°C (85°F) versus August’s 30°C (85°F).
Precipitation is notably higher in September, with 461 mm (18.2 in) over 29 days, compared to 393 mm (15.5 in) over 30 days in August. Humidity levels are also high, with September at 81% and August at 82%, making both months feel quite muggy. For a more detailed look at August weather, you can visit Atenas weather in August.
In September, the weather features a minimum temperature of 18°C (66°F) and a maximum of 29°C (85°F), with an average temperature around 23°C (74°F). The month is notably wet, with a significant precipitation of 461 mm (18.2 in) spread over 29 days and an average humidity of 81%.
Transitioning into October, the temperatures remain consistent, with a minimum of 18°C (66°F) and a maximum of 29°C (84°F), and an average temperature slightly dipping to 23°C (73°F). However, October experiences an increase in precipitation, reaching 639 mm (25.2 in) across 30 days, while humidity levels remain fairly stable at 80%. For more detailed weather information, check out Atenas weather in October.
In September, the weather is characterized by high humidity and frequent rainfall, with an average temperature of 23°C (74°F) and substantial precipitation of 461 mm (18.2 in) over 29 days. In contrast, November sees a slight decrease in rainfall to 251 mm (9.9 in) over 28 days, with similar temperature averages, maintaining a minimum of 18°C (64°F) and a maximum of 29°C (85°F). While the temperatures remain consistent between the two months, November offers a marginally drier atmosphere, making it feel a bit more comfortable. For more detailed information, check out Atenas weather in November.
In comparing the weather between September and December, both months exhibit similar average temperatures, around 23°C (74°F), with September experiencing slightly higher maximum temperatures of 29°C (85°F) compared to December's 30°C (86°F). However, September is characterized by much higher precipitation, totaling 461 mm (18.2 in) across 29 days, while December sees a significant drop, with only 72 mm (2.8 in) over 18 days. Additionally, the humidity in September is notably higher at 81%, contrasting with December's more comfortable 72%. For a more detailed look at December weather, you can visit Atenas weather in December.
As September arrives in Atenas, the weather takes on a distinctly wetter profile compared to other months. Characterized by high humidity and frequent rainfall, this month sees the lush landscapes thrive under the generous precipitation. While temperatures remain mild, averaging a comfortable 23°C, the frequent downpours can lead to a cooling effect, making the air feel more refreshing. This reverberation of activity in the atmosphere provides a stark contrast to the drier, sunnier periods earlier in the year. For those looking to explore the unique charm of Atenas during this rainy season, the vibrant greenery and fewer crowds offer an intimate experience of this beautiful region. For a deeper understanding of what to expect throughout the year, visit Atenas Climate.