September Weather in Washington, United States

Last updated: February 24, 2025

In September, Washington, United States experiences a delightful mix of warm and crisp weather, with an average temperature of 22°C (72°F). The month can see maximum highs reaching a scorching 36°C (97°F), while nights cool down to a refreshing low of 5°C (42°F). Humidity often lingers around 75%, adding a touch of moisture to the air. This month also witnesses 11 days of precipitation, accumulating to about 95 mm (3.8 in), making it a time of transition towards the fall season. Whether basking in the sun or enjoying the refreshing rain, September in Washington offers a unique weather experience for all to savor.

September Temperature in Washington

As summer transitions to fall, September in Washington serves as a gentle yet vibrant bridge between the two seasons. With minimum temperatures settling around 5°C (42°F) and an inviting average of 22°C (72°F), the month offers a pleasant respite before cooler autumn days set in. The warmth peaks with a maximum of 36°C (97°F), reminiscent of summer's embrace, yet nights begin to hint at the crispness of impending fall, creating a unique blend of warmth and chill. This shift is evident as temperatures gradually drop from the sweltering highs of August, showcasing a harmonious balance that encourages outdoor activities amidst the stunning backdrop of early autumn foliage. September, therefore, embodies a transitional charm, promising clear skies while quietly preparing for the cooler months ahead.

September Weather in Washington: Daily Temperature Highs, Lows, and Averages

The chart illustrates September temperature patterns in Washington, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends.
JanFebMarAprMayJunJulAugSepOctNovDec374146566675807772624740
Data source: Temperature data for Washington generated using information from the Copernicus Climate Change Service.
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The average of daily temperatures (24 hours) calculated across all days in the month.

September Precipitation in Washington

In September, Washington experiences a transition as summer gives way to autumn, bringing an average precipitation of 95 mm (3.8 in) over about 11 days of rainfall. This marks a noticeable dip from the peak wetness of July and August, where the state averaged 157 mm (6.2 in) and 140 mm (5.5 in), respectively. As the days shorten and temperatures cool, September's rainfall is a reminder of the shifting seasons, serving as a precursor to the wetter months ahead. Notably, this month’s precipitation stands just slightly below October’s 104 mm (4.1 in), indicating a trend toward increased moisture as the year progresses.

September Precipitation Trends in Washington

The chart displays monthly precipitation patterns in Washington, with values for each month alongside September's data, which is highlighted for easy comparison. It shows the amount of precipitation, providing insights into how September's conditions compare to those of other months.
JanFebMarAprMayJunJulAugSepOctNovDec619887100127118157140951058193
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
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September Humidity in Washington

As summer fades and autumn approaches, September in Washington, United States, experiences a noticeable shift in humidity levels. With an average humidity of 75%, September finds itself perched between the warm, dry conditions of July and August and the wetter months that follow. This slight increase contrasts sharply with the peak summer months, where humidity dips to a comfortable 72% in August, suggesting a gradual return to the more humid conditions typical in the fall. September's humidity is less oppressive than earlier in the year, allowing for more enjoyable outdoor activities, yet it hints at the moisture-rich months to come, with levels rising significantly to 81% by October. This transitional month serves as a gentle reminder of the approaching seasonal changes, bridging the gap between the heat of summer and the chill of autumn.

September Average Humidity in Washington

This chart illustrates the average monthly humidity levels in Washington, with September's data highlighted for easy comparison. It shows the fluctuation in humidity throughout the year, allowing you to see how September's humidity levels compare to other months.
JanFebMarAprMayJunJulAugSepOctNovDec84%83%83%81%78%79%74%72%75%81%85%84%
Data source: Humidity data for September generated using information from the Copernicus Climate Change Service.

September UV Index in Washington

As summer transitions into fall, September in Washington, United States, sees a slight dip in the UV Index, registering at 8—still categorized as very high. This decrease from August's peak of 9 allows for a marginally longer burn time of 15 minutes, reminding residents to remain vigilant against sun exposure. Throughout the year, a clear trend emerges: the UV Index peaks during the summer months, with June, July, and August maintaining a level of 10, while early and late year months like January and December drop to a more moderate 3. As you enjoy the crisp September days, it’s crucial to stay aware of the sun’s potency. For more details on UV levels, visit Washington UV Index.

Maximum UV Index Levels in Washington for September

The chart shows the monthly maximum UV Index (UVI) for Washington in September, representing the highest UV radiation level. The UVI measures the intensity of ultraviolet radiation from the sun, indicating the potential risk of sunburn and UV-related health issues.
JanFebMarAprMayJunJulAugSepOctNovDec357910101098753
Data source: Washington September UVI data generated using information from the Copernicus Climate Change Service.

UV Risk Categories

  •  Extreme (11+): Avoid the sun, stay in shade.
  •  Very High (8-10): Limit sun exposure.
  •  High (6-7): Use SPF 30+ and protective clothing.
  •  Moderate (3-5): Midday shade recommended.
  •  Low (0-2): No protection needed.

September Sunshine in Washington

As summer gives way to autumn, September in Washington, United States, continues to bask in a generous 277 hours of sunshine. This month captures the tail end of a gradual increase in daylight hours that began in the early spring, peaking in July with its dazzling 356 hours. Following the vibrant summer months, where sunshine is plentiful, September's sunlight begins to taper off, heralding a subtle transition toward shorter days, as evidenced by October's anticipated 246 hours. Overall, September stands as a vibrant reminder of summer's lingering warmth, perfectly bridging the gap between the lush brightness of summer and the crisp coolness of fall.

Monthly Sunshine Duration in Washington: September Highlighted

The September sunshine duration represents the total number of hours Washington experiences direct sunlight during the month of September, excluding cloudy or obstructed periods. This chart compares the sunshine duration of September with the other months of the year.
JanFebMarAprMayJunJulAugSepOctNovDec150h180h259h259h281h330h356h321h277h246h226h191h
Data source: Washington September Sunshine duration data generated using information from the Copernicus Climate Change Service.

Chance of Sun in Washington During September

September in Washington, United States, brings a notable uptick in sunny possibilities, with a 53% chance of sunshine gracing the skies. This month stands out as the most favorable for warmth and brightness compared to the surrounding months, particularly after a somewhat dismal August that sees just 34% sunny days. The trend reveals a subtle increase as summer transitions to fall, with March and July both hovering around the 50% mark for sun, but September leads the pack, offering a refreshing blend of mild temperatures and clear skies. As autumn approaches, it seems September is the perfect time to revel in Washington's natural beauty before the rainy season takes hold.

Percentage of Sunny Days in September in Washington

The chart illustrates the percentage of sunny days in Washington throughout the year, with September highlighted. It highlights the variation in sunshine across each month and provides an overview of the typical frequency of sunny days, offering insights into how often Washington experiences clear skies throughout the year.
JanFebMarAprMayJunJulAugSepOctNovDec45%28%53%48%40%38%49%34%53%40%56%37%
Data source: Washington September chance of sun data, generated using information from the Copernicus Climate Change Service.

Daylight Hours in Washington in September

As September arrives in Washington, United States, daylight begins its gentle transition towards the shorter days of autumn. With approximately 12 hours of daylight, September reflects a gradual decline from the summer's peak of 14 hours in June and July, showcasing the subtle shift in the Earth's tilt towards winter. This decrease signifies a departure from the bright, extended days enjoyed in mid-summer, enticing residents to savor the warm hues of early fall while they can. The progression of daylight hours tells a story of seasonal change, as nature prepares for the cozy embrace of fall with its vibrant foliage and crisp air, making September a delightful bridge between summer's bounty and autumn's charm.

Average Daylight Hours in Washington for September

The chart illustrates the variation in daylight duration in Washington throughout the year, with September highlighted. It shows the monthly changes in daylight hours, calculated by summing the hours between sunrise and sunset.
JanFebMarAprMayJunJulAugSepOctNovDec9h 46m10h 44m11h 58m13h 14m14h 18m14h 50m14h 32m13h 36m12h 23m11h 7m10h 1m9h 28m
Data source: Washington daylight hours, calculated by summing the hours between sunrise and sunset for each day.

September Winds in Washington

As summer draws to a close, September in Washington, United States, witnesses a slight uptick in wind speed, averaging 2.6 m/s (6 mph). This marks a departure from the languid breezes of August, which recorded the year’s lowest average at 1.9 m/s (4 mph). As the seasons shift, the winds begin to pick up, hinting at the impending autumnal changes. The overall trend reveals a gradual increase from the summer months, with September transitioning towards the more consistent winds of fall, observed in the following months. Though still gentle, the fresh September air serves as a refreshing reminder that change is on the horizon.

Average September Wind Speed in Washington

The chart displays monthly wind speed patterns in Washington, with values for each month shown alongside September's data, which is highlighted for easy comparison. It illustrates the average wind speed, offering insights into how September's wind conditions compare to the rest of the year.
JanFebMarAprMayJunJulAugSepOctNovDec3.03.23.33.32.82.52.21.92.6 m/s2.82.92.8
Data source: Washington September wind data, generated using information from the Copernicus Climate Change Service.

How September Weather in Washington Compares to Other Months

The weather in Washington 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 Washington and find detailed weather information for every month.

In September, the weather is warm and variable, with temperatures ranging from a cool 5°C (42°F) at night to a scorching 36°C (97°F) during the day, averaging around 22°C (72°F). This month also sees considerable rainfall, with approximately 95 mm (3.8 in) over 11 days, and humidity levels hovering at 75%.

In contrast, January offers a starkly different climate, characterized by much colder temperatures that can plunge to a minimum of -15°C (5°F), with daily averages around 3°C (37°F) and a mild maximum of 22°C (71°F). Although precipitation is slightly lower at 61 mm (2.4 in) across 8 days, the humidity is notably higher at 84%. For more detailed information, explore Washington weather in January.

September and February present stark contrasts in weather. In September, temperatures range from a mild 5°C (42°F) at night to a scorching 36°C (97°F) during the day, with an average of 22°C (72°F). This month sees 95 mm (3.8 in) of precipitation over 11 days, complemented by a comfortable humidity level of 75%. In contrast, February is much colder, with temperatures ranging from a frigid -16°C (4°F) to a comfortable high of 28°C (82°F) and an average of only 5°C (41°F). Precipitation in February is slightly higher at 98 mm (3.9 in) over the same number of days, and humidity reaches 83%. For more insights into February weather, you can check Washington weather in February.

In comparing the weather of September and March, we see notable differences in temperature and precipitation. September typically offers a warm average of 22°C (72°F), with highs reaching up to 36°C (97°F), making it a significantly warmer month than March, which has a much cooler average of 8°C (46°F) and maximum temperatures peaking at 28°C (83°F). While September experiences a minimum temperature of 5°C (42°F) and has an average humidity of 75%, March can see lows drop to -7°C (20°F) with higher humidity levels at 83%. Precipitation is fairly similar, with September receiving 95 mm (3.8 in) across 11 days, while March has slightly less at 87 mm (3.4 in) over 10 days. For more detailed insights, check out Washington weather in March.

When comparing the weather in September and April, there are notable differences in temperature and humidity. In September, temperatures range from a minimum of 5°C (42°F) to a maximum of 36°C (97°F), with an average of 22°C (72°F) and a relative humidity of 75%. In contrast, April experiences cooler temperatures, with a minimum of -2°C (28°F) and a maximum of 32°C (91°F), averaging 14°C (57°F), while humidity is slightly higher at 81%. Both months see similar levels of precipitation, with September receiving 95 mm (3.8 in) and April totaling 100 mm (4.0 in), both over 11 days of rain. For more detailed insights, you can check Washington weather in April.

In September, the weather is characterized by warmer temperatures, with a minimum of 5°C (42°F) and an average of 22°C (72°F), compared to May's lower minimum of 2°C (36°F) and average of 19°C (66°F). Both months experience fairly high humidity levels, with September at 75% and May slightly higher at 78%. However, September enjoys a higher maximum temperature of 36°C (97°F), while May's peak reaches 34°C (94°F). Precipitation is slightly less frequent in September, with 95 mm (3.8 in) over 11 days, compared to May's 127 mm (5.0 in) over 13 days. For more detailed information, you can check out Washington weather in May.

In comparing the weather between September and June, we notice some intriguing similarities and differences. June typically features slightly warmer conditions with an average temperature of 24°C (75°F), compared to September's average of 22°C (72°F). Both months can reach maximum temperatures of 36°C (97°F in September and 98°F in June), yet June starts off at a higher minimum temperature of 9°C (48°F) versus September's cooler 5°C (42°F). Additionally, June experiences more rainfall, with 118 mm (4.7 in) across 12 days, compared to September's 95 mm (3.8 in) over 11 days. Humidity levels are comparable, at 79% in June and 75% in September. For more details on June weather specifics, you can refer to this link: Washington weather in June.

In comparing the weather between September and July, it is evident that July experiences warmer temperatures, with a minimum of 15°C (59°F) and an average of 27°C (81°F), while September's temperatures are cooler, starting at a minimum of 5°C (42°F) and averaging 22°C (72°F). July also peaks at a higher maximum temperature of 38°C (101°F) compared to September's maximum of 36°C (97°F). Precipitation is notably greater in July, totaling 157 mm (6.2 in) over 12 days, compared to September's 95 mm (3.8 in) on 11 days, but both months maintain similar humidity levels of around 74-75%. For more detailed insights, you can check out Washington weather in July.

In September, the weather in Washington, D.C., begins to cool off slightly compared to August. September experiences a minimum temperature of 5°C (42°F) and an average of 22°C (72°F), while August has a higher minimum of 14°C (58°F) and an average temperature of 25°C (77°F). The maximum temperatures are similar, with September reaching up to 36°C (97°F) and August peaking at 37°C (99°F). Precipitation also decreases in September, with 95 mm (3.8 in) over 11 days compared to August's 140 mm (5.5 in) over 15 days. Humidity levels remain fairly consistent, with September at 75% and August slightly lower at 72%. For more detailed information, you can check Washington weather in August.

In September, temperatures typically range from a minimum of 5°C (42°F) to a maximum of 36°C (97°F), with an average of 22°C (72°F). This month experiences about 95 mm (3.8 in) of precipitation over 11 days, accompanied by a humidity level of 75%. In contrast, October sees a drop in average temperatures, with a minimum of 1°C (34°F) and an average of 17°C (62°F), while still reaching a maximum of 36°C (97°F) on occasion. Precipitation increases slightly to 104 mm (4.1 in) spread over 9 days, and humidity rises to 81%. For more detailed information, you can check Washington weather in October.

In September, temperatures are much warmer, with an average of 22°C (72°F) and highs reaching up to 36°C (97°F). The month experiences considerable humidity at 75% and roughly 95 mm (3.8 in) of precipitation over 11 days. In contrast, November brings a significant drop in temperatures, with an average of 8°C (47°F) and a maximum of 25°C (78°F), along with colder mornings dipping to -6°C (21°F). Precipitation is slightly lower at 81 mm (3.2 in) but occurs over fewer days, with seven rainy days and higher humidity at 85%. For more detailed weather insights, you can check Washington weather in November.

In September, the weather is significantly warmer, with temperatures ranging from a minimum of 5°C (42°F) to a maximum of 36°C (97°F), and an average of 22°C (72°F). The month experiences around 95 mm (3.8 in) of precipitation over approximately 11 days, accompanied by a humidity level of 75%. In contrast, December brings much cooler conditions, with temperatures dipping from a minimum of -10°C (13°F) to a maximum of 20°C (69°F), and an average temperature of just 5°C (41°F). Precipitation in December is slightly lower at 93 mm (3.7 in), falling over 9 days, and the humidity rises to 84%. For more detailed insights, you can refer to Washington weather in December.

Compare Washington's Climate with Cities Worldwide

Conclusion: What to Expect From September Weather in Washington

As summer gives way to fall, September in Washington showcases a delightful transition with pleasantly warm days and cooler evenings. This month is characterized by a balanced blend of humidity and occasional rain, creating a fresh atmosphere that sets it apart from the sweltering heat of July and August. While temperatures can peak at a sweltering 36°C, the average remains comfortable, inviting both locals and visitors to embrace outdoor activities. With around 11 days of precipitation, September's rainfall is a gentle reminder of the coming autumn. For more detailed insights on Washington's weather patterns throughout the year, check out Washington Climate.