Last updated: February 24, 2025
In September, National Harbor, United States experiences a dynamic climate, characterized by a maximum temperature soaring to 37°C (99°F) and a comfortable average of 22°C (73°F). With minimums dipping to 6°C (44°F), the weather provides a distinctive blend of warmth and coolness. Rainfall is notable, with 93 mm (3.7 in) recorded over 11 days, contributing to a humidity level of 75% that enhances the lush atmosphere. Visitors can expect a mix of sunny days and occasional showers, making it an ideal time to explore all that National Harbor has to offer.
In September, National Harbor, United States, enjoys a delightful transition into fall. With minimum temperatures averaging around 6°C (44°F) and a comfortable mean of 22°C (73°F), the weather invites outdoor activities while offering a reprieve from the summer heat. The highs can still reach up to 37°C (99°F), reflecting the tail end of summer's warmth. This month marks a significant cooling trend compared to the sizzling peak of July and August, making it an ideal time for visitors to explore the vibrant surroundings. As daylight begins to wane and autumn colors start to emerge, September is a sweet spot for those seeking pleasant temperatures and stunning views.
In September, National Harbor experiences a notable shift in weather patterns, with precipitation totaling 93 mm (3.7 in) over the month. This amount, while significant, marks a decrease from the peak rainfall of August, which recorded 146 mm (5.7 in). With 11 days of rain, September reflects a moderately wet month that follows the summer's peak precipitation, suggesting a gradual transition toward autumn. The overall trend across the months indicates a buildup of rain from the earlier part of the year, culminating in the summer, then tapering off as fall approaches. As precipitation decreases, visitors can often enjoy clearer days, making it an ideal time to explore the scenic beauty of National Harbor.
In September, humidity levels in National Harbor settle at a comfortable 75%, slightly higher than the summer months of July and August, which experienced their lowest humidity levels of 74% and 72%, respectively. This subtle increase marks the transition toward the cooler months, with October seeing humidity levels rise again to 81%. Overall, the year showcases a trend of higher humidity during the winter months, peaking at 85% in November, while the summer months generally offer more breathable conditions. As the season shifts, September serves as a gentle reminder of the changing climate, blending summer warmth with the promise of the autumnal chill ahead.
In September, the UV Index in National Harbor stands at 8, categorizing the exposure as very high with a burn time of just 15 minutes. This month marks a slight dip from the peak summer months, where the UV Index consistently reached 10. However, it remains critical for sun safety as the intensity is still significant. As we transition into fall, the UV levels decrease but stay noticeably elevated compared to earlier in the year, such as in January and February, when the index averaged around 3 to 5. To stay protected during these sunny days, it's important to apply sunscreen and wear protective clothing. For more detailed information, visit National Harbor UV Index.
UV Risk Categories
As summer gracefully transitions into fall, September brings a delightful 276 hours of sunshine to National Harbor, United States. This month showcases a gentle decline from the sun-drenched peaks of July and August, which basked in 357 and 321 hours, respectively. The consistent warmth persists as September retains a significant amount of sunlight compared to the earlier months of the year, which struggled to reach even 259 hours until the blossoming days of spring. As autumn approaches, the days may shorten, but the lingering warmth encourages outdoor celebrations and scenic explorations, making September a perfect month to enjoy the vibrant natural beauty of this picturesque location.
September stands out as a promising month for sun seekers in National Harbor, boasting a 55% chance of sunny weather. This increase in sunny days follows the typical summer decline, with August dipping to 35%. As summer transitions into fall, September marks a slight resurgence in sunshine, offering a refreshing contrast to the overcast days that precede it. Interestingly, this month outshines both the earlier months and the oncoming autumn, reflecting a trend where individuals can expect more favorable weather conditions as they prepare for outdoor activities and events. With a notable spike in sun likelihood, September is an ideal time to bask in the warmth before the cooler months set in.
As September unfolds in National Harbor, the daylight begins to wane, offering 12 hours of sunlight compared to the summer's peak of 14 hours in June, July, and early August. This gradual reduction marks the transition from the vibrant, sun-soaked days of summer to the cooler embrace of autumn. With each passing month, the daylight duration decreases, peaking in May and then steadily declining towards the winter months where it hits a low of 9 hours in January and December. This rhythmic dance of daylight illuminates the changing seasons, inviting residents and visitors alike to savor the softer glow of September as nature prepares for its seasonal shift.
As September rolls into National Harbor, the breeze picks up slightly with an average wind speed of 2.5 m/s (6 mph), a refreshing change after the calm of summer. Throughout the year, wind patterns exhibit a clear trend; following a peak in spring, the winds gradually soften during the hot months of July and August, reaching a low of 1.9 m/s (4 mph). However, as autumn approaches, gusts begin to regain momentum, hinting at the transitioning seasons ahead. This subtle increase in wind speed not only enhances the natural beauty of the harbor but also provides a perfect backdrop for outdoor activities, making it an ideal time for residents and visitors to revel in the fresh air and picturesque views.
The weather in National Harbor 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 National Harbor and find detailed weather information for every month.
September and January present stark contrasts in weather. While September boasts mild temperatures ranging from a minimum of 6°C (44°F) to a maximum of 37°C (99°F), January experiences much colder conditions, with temperatures dipping as low as -14°C (7°F) and peaking at 22°C (71°F). September also tends to be more humid, with an average humidity of 75%, compared to January's 84%. Additionally, September sees more precipitation, accumulating 93 mm (3.7 in) across 11 days, whereas January receives only 61 mm (2.4 in) over 7 days. For a detailed look at January weather, check out National Harbor weather in January.
In September, the weather is typically warmer, with average temperatures around 22°C (73°F) and maximums reaching as high as 37°C (99°F), accompanied by a fair amount of humidity at 75%. The month experiences around 93 mm (3.7 in) of precipitation over approximately 11 days. In contrast, February presents a much colder climate, with average temperatures dropping to a chilly 5°C (42°F) and minimums plummeting to -14°C (7°F). Although February has a similar amount of precipitation, 96 mm (3.8 in) over the same number of days, the increased humidity at 83% adds a layer of chilliness to the atmosphere. To learn more about specific weather conditions in February, you can view National Harbor weather in February.
When comparing the weather in September and March, notable differences emerge. September typically boasts a much warmer climate, with average temperatures reaching 22°C (73°F) and highs soaring up to 37°C (99°F). In contrast, March experiences cooler temperatures, with an average of 8°C (47°F) and maximums of only 29°C (84°F). Precipitation levels are somewhat similar, with September receiving 93 mm (3.7 in) over 11 days and March slightly less at 82 mm (3.2 in) over 9 days. Humidity is also higher in March, sitting at 83%, compared to 75% in September. For more information on March weather, you can refer to this link: National Harbor weather in March.
When comparing the weather in September and April, notable differences emerge in temperature and humidity. September boasts warmer temperatures, with a minimum of 6°C (44°F) and an average of 22°C (73°F), soaring to a maximum of 37°C (99°F). In contrast, April starts off cooler, with a minimum of -1°C (31°F) and an average of 14°C (58°F), though it can reach as high as 33°C (92°F). Both months experience similar rainfall, with September receiving 93 mm (3.7 in) and April slightly wetter at 102 mm (4.0 in), both spread across 11 days. Humidity levels also tend to be slightly higher in April at 81%, compared to September's 75%. For more detailed weather insights, refer to National Harbor weather in April.
When comparing the weather in September and May, notable differences emerge in temperature and precipitation patterns. September boasts higher average temperatures, ranging from a minimum of 6°C (44°F) to a maximum of 37°C (99°F), with an average of 22°C (73°F). In contrast, May exhibits slightly cooler temperatures, with lows around 3°C (37°F) and highs reaching 35°C (95°F), averaging 19°C (67°F). Precipitation is more abundant in May, totaling 121 mm (4.8 in) over 12 days, compared to September's 93 mm (3.7 in) over 11 days. Additionally, both months feature relatively high humidity levels, with September at 75% and May slightly higher at 78%. For more details, check out National Harbor weather in May.
When comparing the weather in September and June, we see some notable differences. September typically has a slightly lower minimum temperature of 6°C (44°F) compared to June's 9°C (49°F), while both months experience similar maximum temperatures, peaking at around 37°C (98-99°F). The average temperature in June is marginally higher at 24°C (76°F) versus September's 22°C (73°F). Additionally, June experiences more precipitation, with 107 mm (4.2 in) over 13 days, compared to September’s 93 mm (3.7 in) over 11 days. Humidity levels are also higher in June at 79%, compared to September's 75%. For more detailed insights, check out National Harbor weather in June.
When comparing the weather in September and July, it's evident that July tends to be warmer overall. In July, the minimum temperature is 16°C (61°F) with an average of 27°C (81°F) and a maximum reaching up to 38°C (102°F). In contrast, September sees a much cooler minimum of 6°C (44°F) and an average temperature of 22°C (73°F), while still hitting highs of 37°C (99°F). Additionally, July experiences more precipitation, with 132 mm (5.2 in) spread over 12 days, compared to September's 93 mm (3.7 in) over 11 days. Humidity levels are relatively similar, with July at 74% and September slightly higher at 75%. For a detailed look at July conditions, you can visit National Harbor weather in July.
In comparing the weather between September and August, September showcases a notable drop in minimum temperatures, ranging from 6°C (44°F) at night compared to August's milder minimum of 15°C (59°F). Despite having the same maximum temperature of 37°C (99°F), September’s average temperature is slightly cooler at 22°C (73°F) versus August’s 25°C (78°F). Rainfall in September totals 93 mm (3.7 in) over 11 days, which is less than August’s higher precipitation of 146 mm (5.7 in) across 15 days. Humidity remains relatively high in both months, with September at 75% and August slightly lower at 72%. For a more detailed look at August weather, you can visit National Harbor weather in August.
September typically boasts warmer temperatures with an average high of 22°C (73°F) and a maximum reaching 37°C (99°F), while October experiences a cooler average of 17°C (63°F) and peaks at 36°C (97°F). Precipitation increases slightly in October, with 105 mm (4.2 in) over 9 days compared to 93 mm (3.7 in) over 11 days in September. Additionally, October sees a rise in humidity, averaging 81% compared to September's 75%. For a more detailed overview, you can explore National Harbor weather in October.
September and November present distinctly contrasting weather conditions. In September, temperatures range from a comfortable minimum of 6°C (44°F) to a scorching maximum of 37°C (99°F), with an average of 22°C (73°F). The month experiences significant rainfall, totaling 93 mm (3.7 in) over 11 days, coupled with a humidity level of 75%. In contrast, November brings much cooler temperatures, featuring a minimum of -5°C (23°F) and an average of 9°C (48°F), peaking at 26°C (78°F). Precipitation decreases to 77 mm (3.0 in) spread over just 7 days, and humidity rises slightly to 85%. For more detailed information about November weather specifics, you can refer to National Harbor weather in November.
September and December present starkly contrasting weather patterns. In September, temperatures typically range from a minimum of 6°C (44°F) to a sizzling maximum of 37°C (99°F), with an average temperature of 22°C (73°F). This month also experiences considerable humidity at 75% and sees around 93 mm (3.7 inches) of precipitation over 11 days. Conversely, December brings much colder conditions, featuring a minimum of -10°C (14°F) and a maximum of 20°C (69°F), with an average of just 5°C (42°F). Precipitation is slightly lower at 89 mm (3.5 inches) but falls over fewer days (9), while humidity rises to 84%. For more details, check out the National Harbor weather in December.
September in National Harbor marks a transitional shift from the warm summer months, bringing a blend of mild temperatures and increased humidity levels. As the peak heat of summer eases, you can expect cooler evenings, making it a refreshing time to explore the area. However, the month also presents its share of rainy days, reminding visitors that autumn is on the horizon. With average conditions leaning towards comfort, September provides an ideal balance for those looking to enjoy both sunny afternoons and cozy evenings. For a deeper insight into what to expect throughout the year, check out the National Harbor Climate.