Last updated: February 24, 2025
September in Seattle presents a delightful mix of mild temperatures and a hint of autumn. The average high reaches 30°C (86°F), while nights cool down to a comfortable minimum of 8°C (46°F), creating a pleasant daily range of 16°C (62°F). Although the month experiences approximately 100 mm (3.9 in) of rainfall over 12 days, the humidity sits at a moderate 62%, contributing to the lush greenery that the region is famous for. Whether you're exploring the vibrant city or enjoying the surrounding nature, September in Seattle offers a beautiful transition into fall.
As September arrives in Seattle, temperatures begin to shift, welcoming the first hints of autumn while still enjoying late-summer warmth. The minimum temperature settles around 8°C (46°F), offering a comfortable start to the month, while the average hovers at a pleasant 16°C (62°F). By day, the cities bask in warmth, with maximum temperatures peaking at 30°C (86°F), reflecting a gradual transition from the heat of summer months. This trend highlights Seattle’s characteristic mild climate, where each season's flavors are evident yet seamlessly blend into one another, inviting residents and visitors to relish both warm days and cooler evenings.
As summer gives way to autumn, September in Seattle sees a notable increase in precipitation, with 100 mm (3.9 in) of rainfall over about 12 days. This marks a shift from the particularly dry months of July and August, which averaged less than 2 inches combined. The transition signals the beginning of the wetter season, as rainfall increases significantly in the following months, peaking in December with an impressive 196 mm (7.7 in). The gradual ramp-up in moisture levels during September serves as a reminder of Seattle's characteristic rainy climate, paving the way for the more persistent downpours that October and November are known for.
September in Seattle marks a notable shift in humidity, dipping to 62%, the lowest level of the year following the summer months. This decrease continues the trend of declining moisture levels from the humid peak experienced in spring and early summer, where humidity hovered around 81% to 87%. As the city transitions from the sun-soaked days of August—when the humidity is a more comfortable 63%—to the crisp, cooler autumn air that follows, residents can enjoy a brief reprieve from the typical dampness that characterizes the Pacific Northwest. However, this respite is short-lived, as humidity levels rebound dramatically in October, climbing back to 83%. The evolving patterns of humidity reflect Seattle’s unique climate, offering a taste of drier weather before the familiar moisture returns with the falling leaves.
In September, Seattle experiences a UV Index of 7, marking a transition from the height of summer but still classified as high exposure. As the sun begins to lower in the sky, residents can enjoy approximately 25 minutes of burn time without protection. Interestingly, this month maintains a notable trend observed throughout the summer—though the UV Index has slightly decreased from the peak levels of 8 and 9 in July and August, it remains significantly elevated compared to the cooler months. Such a pattern emphasizes the continued need for sun protection as we enter early fall. For detailed insights and daily updates, check out the Seattle UV Index.
UV Risk Categories
As summer fades, September in Seattle still boasts a generous 254 hours of sunshine, making it a splendid month to enjoy the lingering warmth. Historically, this marks a significant dip from the sun-soaked peak of July, which dazzles with 361 hours of light, but it ranks comfortably above the cloudier months ahead, such as October with only 190 hours. This transition is marked by a gradual decline in sunlight as the city prepares for the drizzly days of autumn. Nevertheless, September remains a treasure trove of bright days, inviting locals and visitors alike to bask in the sun before the seasons change.
As summer transitions into autumn, September in Seattle brings a noticeable shift in the likelihood of sunny weather. With a 36% chance of sun, this month offers a pleasant respite compared to the damp gloom of the winter months. While it's certainly sunnier than the depths of January and December, September also marks a decline from the summer's peak, where July enjoys a robust 63% sunshine. Interestingly, despite the decrease, the weather remains relatively favorable compared to the spring months. This trend highlights September as a transitional period, where sunny days can still be savored, making it a delightful time for outdoor activities before the autumn chill sets in.
As September arrives in Seattle, the city begins to transition from the long summer days of July and August, which boast up to 15 hours of daylight, to a more moderate 12 hours. This gradual reduction signals the onset of autumn, as sunlight dwindles and the lush greenery of the Pacific Northwest prepares for seasonal change. With daylight hours starting to decline, September serves as a gentle reminder of the shorter days ahead, moving toward the 10 hours expected in October. The rhythm of daylight in Seattle reflects the cyclical nature of the seasons, inviting residents to savor the remaining golden hours before the winter months set in.
As September arrives in Seattle, the city's breezes begin to shift, bringing an average wind speed of 2.5 m/s (6 mph), which aligns closely with the calmness of the summer months. Following a gentle July that recorded the year's lowest winds, the autumn transition introduces a slight increase in airflow reminiscent of the seasonal ebb and flow. While September mirrors the breezy conditions seen in May and March, it paves the way for October's uptick in wind speeds to 2.9 m/s (6 mph) and prepares the city for the brisker gales of November and December. This subtle shift not only captures the essence of Seattle's dynamic climate but also heralds a return to the invigorating winds that define the city's fall.
The weather in Seattle 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 Seattle and find detailed weather information for every month.
September and January present stark contrasts in weather conditions. In September, the temperatures range from a mild 8°C (46°F) at night to a warm 30°C (86°F) during the day, with an average of 16°C (62°F). The month sees about 100 mm (3.9 in) of precipitation over approximately 12 days, and the humidity hovers around 62%. In contrast, January is much colder, featuring a minimum temperature of -7°C (19°F) and a maximum of 14°C (57°F), with an average of 6°C (43°F). This month experiences significantly higher precipitation at 175 mm (6.9 in) across 16 days, combined with a higher humidity level of 86%. For further details on winter conditions, you can visit Seattle weather in January.
September and February offer starkly contrasting weather conditions. In September, temperatures range from a mild 8°C (46°F) at night to a warm 30°C (86°F) during the day, with an average of 16°C (62°F). This month experiences about 100 mm (3.9 in) of precipitation over approximately 12 days, accompanied by a humidity level of 62%. In contrast, February features much colder temperatures, with minimums plummeting to -10°C (14°F) and a maximum of 14°C (58°F), resulting in an average temperature of just 5°C (41°F). Precipitation is significantly higher at 177 mm (7.0 in), falling over 19 days, and humidity also rises considerably to 86%. The dramatic differences in temperature and moisture between these months highlight the transition from late summer warmth to the depths of winter. For more details, check out Seattle weather in February.
September and March present contrasting weather profiles. In September, temperatures range from a pleasant 8°C (46°F) to a warm 30°C (86°F), with an average of 16°C (62°F). The month experiences around 100 mm (3.9 in) of precipitation over approximately 12 days, contributing to a moderate humidity level of 62%. In contrast, March brings cooler conditions, with temperatures dipping as low as -1°C (31°F) and peaking at 22°C (72°F), averaging around 7°C (46°F). Precipitation is slightly higher at 126 mm (4.9 in), occurring over 17 days, and the humidity also increases to 87%. For a more detailed look at March weather, check out Seattle weather in March.
When comparing the weather between September and April, notable differences emerge. September typically experiences milder temperatures, with a minimum of 8°C (46°F) and a comfortable average of 16°C (62°F), peaking at an occasional maximum of 30°C (86°F). In contrast, April tends to be cooler, starting at a minimum of 1°C (34°F) and averaging just 10°C (50°F), climbing to a maximum of 24°C (75°F). Precipitation levels are somewhat similar, with September receiving 100 mm (3.9 in) over 12 days and April slightly wetter at 117 mm (4.6 in) across 14 days. Additionally, April's humidity is higher at 84%, compared to September's 62%, making for a more damp feel during the earlier fall month. For more detailed information on April weather, visit Seattle weather in April.
September and May exhibit notable differences in weather patterns. September features a wider temperature range, with minimums of 8°C (46°F) and maximums reaching up to 30°C (86°F), while May has slightly cooler temperatures, ranging from a minimum of 5°C (42°F) to a maximum of 28°C (82°F). Precipitation levels in September are higher, averaging 100 mm (3.9 in) over 12 days, compared to May's 68 mm (2.7 in) over the same number of days. Moreover, humidity levels are noticeably different, with September at 62% and May at a more humid 81%. For more insights into the weather during this vibrant month, check out Seattle weather in May.
When comparing the weather in September and June, we notice that both months experience similar minimum temperatures, starting at around 8°C (46°F). However, June typically boasts a slightly higher average temperature of 17°C (62°F) compared to September's average of 16°C (62°F). The maximum temperatures in June can reach up to a scorching 38°C (101°F), significantly higher than September's peak of 30°C (86°F). Furthermore, June has a higher humidity level at 82%, which contributes to a warmer feel, while September's humidity is a bit lower at 62%. Additionally, precipitation is more frequent in September, with 100 mm (3.9 in) over 12 days, compared to June's 63 mm (2.5 in) over 9 days. For a more detailed look at June in the Emerald City, check out Seattle weather in June.
In comparing the weather between September and July, we observe distinct differences in temperature, precipitation, and humidity. September offers a wider temperature range, with minimums around 8°C (46°F) and maximums peaking at 30°C (86°F), giving it an average of 16°C (62°F). In contrast, July presents milder temperatures, with minimums of 11°C (52°F) and maximums reaching 32°C (91°F), averaging 19°C (67°F).
Precipitation also varies greatly, as September experiences more rainfall with about 100 mm (3.9 in) over 12 days, while July enjoys significantly less at just 18 mm (0.7 in) and only 5 days of rain. Moreover, the humidity is higher in July at 79%, compared to September's more moderate 62%. For more details on July weather, you can check out Seattle weather in July.
In comparing the weather between September and August, we see notable differences in temperature and precipitation. September experiences a wider temperature range, with minimums dropping to 8°C (46°F) and maximums reaching up to 30°C (86°F), while August averages between 10°C (51°F) and a high of 33°C (93°F). Rainfall also contrasts sharply; September has significantly more precipitation at 100 mm (3.9 in) over 12 days, compared to August's modest 16 mm (0.6 in) over just 5 days. Additionally, humidity levels remain similar, with September at 62% and August slightly higher at 63%. For more details, check out Seattle weather in August.
September typically experiences warmer temperatures with a minimum of 8°C (46°F) and a maximum of 30°C (86°F), leading to an average of 16°C (62°F). However, it also sees a decent amount of precipitation, totaling around 100 mm (3.9 in) over approximately 12 days, with humidity levels around 62%. In contrast, October brings cooler conditions, with temperatures ranging from a minimum of -1°C (30°F) to a maximum of 23°C (74°F) and an average of 11°C (52°F). This month also has increased precipitation, accumulating 155 mm (6.1 in) over 15 days, and the humidity rises to 83%. For more detailed insights, check out Seattle weather in October.
September and November present contrasting weather experiences. In September, temperatures generally range from a mild 8°C (46°F) at night to a warm 30°C (86°F) during the day, with an average of 16°C (62°F). The month sees about 100 mm (3.9 in) of precipitation over approximately 12 days, contributing to a comfortable humidity level of 62%. In stark contrast, November brings much cooler temperatures, with a minimum of -1°C (30°F) and an average of only 8°C (47°F). Rain is more prevalent, with 181 mm (7.1 in) falling over 18 days, and humidity levels rise significantly to 89%. For those curious about the specifics of Seattle's weather in November, you can find more details here: Seattle weather in November.
September and December present stark contrasts in weather conditions. In September, temperatures typically range from a mild 8°C (46°F) at night to a warm 30°C (86°F) during the day, with an average of 16°C (62°F). While precipitation occurs on about 12 days, totaling around 100 mm (3.9 in), humidity hovers at 62%, creating a relatively comfortable atmosphere. In contrast, December brings much colder temperatures, with nighttime lows dropping to -7°C (20°F) and daytime highs only reaching up to 14°C (58°F), resulting in an average of 6°C (42°F). The month is also wetter, accumulating approximately 196 mm (7.7 in) of precipitation over about 19 days, coupled with heightened humidity levels at 88%. For more details about the weather in December, you can visit Seattle weather in December.
As summer transitions into fall, September in Seattle showcases a unique blend of temperate conditions unlike any other month. With temperatures comfortably averaging around 16°C (62°F), days can still heat up to a maximum of 30°C (86°F), offering a pleasant contrast to the cooler months ahead. However, be prepared for a touch of rain, as September sees about 100 mm of precipitation, with approximately 12 days of showers, elevating the humidity to 62%. This combination of warmth and moisture creates a refreshing ambiance, making it a beautiful time to explore the city's parks and waterfronts. For a comprehensive overview of how Seattle's weather evolves throughout the year, visit Seattle Climate.