Mercer Island Weather in September

September in Mercer Island typically sees daytime highs of 22°C (72°F) and nighttime lows of 12°C (54°F). Expect some rainfall during the month. It falls within the summer season.

Rainfall in Mercer Island in September

Typically around 10 days of rainfall are expected, averaging 52 mm (2 in) for the month. Expect a fairly normal spread of rainfall this month, with no particular pattern of very heavy or very persistent showers.

Temperature in Mercer Island in September

September tends to be one of the perfect months in Mercer Island, with 22°C (72°F) in the afternoon and 12°C (54°F) overnight. Summer occurs in September. Temperatures can feel cooler in the morning and evening, so layering is often the best approach. With overnight lows of 12°C (54°F), evenings can feel noticeably cooler than the daytime. An extra layer is a good idea, though the cool air makes for a good night's sleep.

Sunshine in Mercer Island in September

Enjoy a sunny month with about 220 hours of sunshine, the clear skies make Mercer Island even more beautiful.

Wind Speed in Mercer Island in September

Wind speeds average 4 m/s (8 knots) during September. At this speed, expect moderate winds that can raise dust and move small branches. Since this is an average, some days have gentle light winds while others experience stronger breezes that are quite noticeable.

If you favor pleasant temperatures and minimal rainfall, September is one of the best months to visit Mercer Island.

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• January
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For a detailed overview over the year and the best time to visit the United States of America, check out our Mercer Island's climate page.

Mercer Island Temperature in September

Min Temperature 12°C (54°F)  

Max Temperature 22°C (72°F)  

Chance of Rain 33%  

Precipitation 52 mm (2 in)  

Rainy days 10 days  

Humidity 73% *  

Windspeed 4 m/s (8 knots) *  

Sunshine 220 hours *  

Percentage Sunshine 59% *  

* Data from: Seattle, the United States of America (15 KM, 9 Miles).

What to Wear in Mercer Island in September

For Mercer Island in September, you'll want flexible clothing. It's wise to pack cotton shirts, comfortable shorts, and a pair of jeans for cooler evenings. A light sweater or jacket is useful for air-conditioned spaces (like buses) or unexpected cool moments. Rain is likely on several days, so bring a good rain jacket. You'll definitely want to pack sunglasses and sunscreen. There will be plenty of bright sunshine this month.

What To Do in Mercer Island in September

We rated the following activities from 1 (least suitable) to 10 (best) to do.

Cycling

10/10

Walking

10/10

Barbeque

9/10

Camping

8/10

Outdoor sports

10/10

Select a Month

Check the conditions for any month of the year.

• January
• February
• March
• April

• May
• June
• July
• August

• September
• October
• November
• December

For a detailed overview over the year and the best time to visit the United States of America, check out our Mercer Island's climate page.

More climate data for Mercer Island

Temperature Rainfall Sunshine Humidity Wind Speed

See the full Mercer Island climate overview or explore weather in the United States of America.