September weather forecast
Seattle, WA

Beautiful dusk skyline over the giant skyscrapers of Seattle, Washington
Beautiful dusk skyline over the giant skyscrapers of Seattle, Washington

Weather in September

The first month of the autumn, September, is still a pleasant month in Seattle, Washington, with temperature in the range of an average low of 50.5°F (10.3°C) and an average high of 69.6°F (20.9°C).

Temperature

In Seattle, the average high-temperature in September slightly decreases from a warm 76.3°F (24.6°C) in August to a pleasant 69.6°F (20.9°C). In September, the average low-temperature is 50.5°F (10.3°C).

Humidity

In Seattle, the average relative humidity in September is 75%.

Rainfall

In Seattle, during September, the rain falls for 6 days and regularly aggregates up to 0.28" (7mm) of precipitation. Throughout the year, there are 84.2 rainfall days, and 5.2" (132mm) of precipitation is accumulated.

Snowfall

In Seattle, Washington, snow does not fall in April through October and December.

Ocean temperature

In Seattle, the average water temperature is 53.2°F (11.8°C).
Note: At temperatures below 50°F (10°C), swimming in a suitably protected swimsuit is feasible; otherwise, cold shock and loss of breathing control are imminent. Even a short swim, without thermal protection, at temperatures around 55.4°F (13°C) is not comfortable.

Daylight

In Seattle, the average length of the day in September is 12h and 33min.
On the first day of September, sunrise is at 6:28 am and sunset at 7:50 pm. On the last day of the month, sunrise is at 7:07 am and sunset at 6:51 pm PDT.

Sunshine

In Seattle, the average sunshine in September is 9.4h.

UV index

In Seattle, the average daily maximum UV index in September is 4. A UV Index of 3 to 5 symbolizes a moderate threat to health from unprotected exposure to Sun's UV rays for the ordinary person.
Note: In September, the average maximum UV index of 4 translate into the following recommendations:
Take precautions. Light skin individuals may get burned in less than 30 minutes. The solar radiation is most powerful near the mid-day, so the exposure to the direct Sun should be reduced accordingly. On bright days sunglasses that block both UVA and UVB rays should be worn. A hat with a wide brim is extremely helpful, as it can prevent roughly 50% of UV radiation from reaching the eyes.
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FAQ

What is the temperature in September in Seattle?

The average high-temperature, in September, is 69.6°F (20.9°C), while the average low-temperature is 50.5°F (10.3°C).

What is the average humidity in September in Seattle?

The average relative humidity in September is 75%.

How many days does it rain in September in Seattle?

In Seattle, Washington, during September, the rain falls for 6 days and regularly aggregates up to 0.28" (7mm) of precipitation.

When it does not snow in Seattle?

April through October and December are months without snowfall.

What is the water temperature in September in Seattle?

In September, the average ocean temperature in Seattle, Washington, is 53.2°F (11.8°C). At temperatures below 50°F (10°C), swimming in a suitably protected swimsuit is feasible; otherwise, cold shock and loss of breathing control are imminent. Even a short swim, without thermal protection, at temperatures around 55.4°F (13°C) is not comfortable.

How many hours of daylight does Seattle have in September?

In Seattle, Washington, the average day length in September is 12h and 33min.

What time are sunrise and sunset in September in Seattle?

In September, on the first day of the month, sunrise is at 6:28 am and sunset at 7:50 pm. On the last day of the month, in Seattle, sunrise is at 7:07 am and sunset at 6:51 pm PDT.

How long on average sun shines in September in Seattle?

In September, the average sunshine duration in Seattle is 9.4h.

How high is the UV index in September in Seattle?

In September, the average daily maximum UV index in Seattle is 4. A UV Index value of 3 to 5 symbolizes a moderate vulnerability from exposure to Sun's UV rays.
Average humidity
Average rainfall days
Average snowfall
Average snowfall days
Average sunshine days
Average UV index
Average cloud cover
Average visibility

Average temperature in September
Seattle, WA

Average temperature in September - Seattle, WA
  • Average high temperature in September: 69.6°F

The warmest month (with the highest average high temperature) is August (76.3°F).
The month with the lowest average high temperature is December (43.7°F).

  • Average low temperature in September: 50.5°F

The month with the highest average low temperature is August (54°F).
The coldest month (with the lowest average low temperature) is December (35.1°F).

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Average pressure in September
Seattle, WA

Average pressure in September - Seattle, WA
  • Average pressure in September: 30.01"Hg

The month with the highest atmospheric pressure is January (30.1"Hg).
The months with the lowest atmospheric pressure are March, August and September (30.01"Hg).

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Average wind speed in September
Seattle, WA

Average wind speed in September - Seattle, WA
  • Average wind speed in September: 3.9mph

The windiest month (with the highest average wind speed) is March (5.3mph).
The calmest months (with the lowest average wind speed) are July and August (3.5mph).

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Average humidity in September
Seattle, WA

Average humidity in September - Seattle, WA
  • Average humidity in September: 75%

The month with the highest relative humidity is January (85%).
The month with the lowest relative humidity is July (69%).

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Average rainfall in September
Seattle, WA

Average rainfall in September - Seattle, WA
  • Average rainfall in September: 0.28"

The wettest month (with the highest rainfall) is December (0.87").
The driest months (with the least rainfall) are July and August (0.12").

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Average rainfall days in September
Seattle, WA

Average rainfall days in September - Seattle, WA
  • Average rainfall days in September: 6 days

The month with the highest number of rainy days is November (9.1 days).
The month with the least rainy days is August (2.8 days).

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Average snowfall in September
Seattle, WA

Average snowfall in September - Seattle, WA
  • Average snowfall in September: 0"

The month with the highest snowfall is February (0.71").
The months with the least snowfall are April, May, June, July, August, September, October and December (0").

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Average snowfall days in September
Seattle, WA

Average snowfall days in September - Seattle, WA
  • Average snowfall days in September: 0 days

The month with the highest number of snowfall days is February (1.9 days).
The months with the least snowfall days are May, June, July, August, September and October (0 days).

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Average sea temperature in September
Seattle, WA

Average sea temperature in September - Seattle, WA
  • Average sea temperature in September: 53.3°F

The best month for swimming (with the highest average sea temperature) is August (53.5°F).
The coldest month (with the lowest average sea temperature) is February (45.3°F).

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Average daylight in September /
Average sunshine in September
Seattle, WA

Average daylight in September / Average sunshine in September - Seattle, WA
  • Average daylight in September: 12h and 33min

The month with the longest days is June (Average daylight: 15h and 55min).
The month with the shortest days is December (Average daylight: 8h and 31min).

  • Average sunshine in September: 9h and 24min

The month with the most sunshine is August (Average sunshine: 10h and 42min).
The month with the least sunshine is December (Average sunshine: 4h and 18min).

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Average sunshine days in September
Seattle, WA

Average sunshine days in September - Seattle, WA
  • Average sunshine days in September: 21.1 days

The month with the most sunshine days is August (25.9 days).
The month with the least sunshine days is November (16.8 days).

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Average UV index in September
Seattle, WA

Average UV index in September - Seattle, WA
  • Average UV index in September: 4

The month with the highest UV index is July (UV index 6).
The months with the lowest UV index are January, February, November and December (UV index 2).

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Average cloud cover in September
Seattle, WA

Average cloud cover in September - Seattle, WA
  • Average cloud cover in September: 33

The month with the most cloud cover is December (Cloud cover 56).
The month with the least cloud cover is August (Cloud cover 25).

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Average visibility in September
Seattle, WA

Average visibility in September - Seattle, WA
  • Average visibility in September: 6mi

The months with the highest visibility are April, May, June, July, August, September and October (6mi).
The months with the lowest visibility are January, February, March, November and December (5mi).

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