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Hourly Forecast
Daylight Hours
06:53
Sunrise
19:13
Sunset
Moon
Waxing Crescent
12:18
Moonrise
20:26
Moonset
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Weather in Mercer Island today, September 15, 2026
Expect a mostly clear day in Mercer Island on September 15, 2026, with sunshine dominating from morning through evening. Cloud should stay limited, so the overall feel remains bright and settled. The first half of the day looks overcast, as cloud amounts reach about 99% around 11:00. Brighter weather, if it comes, waits until later.
Expect highs of 19°C and cooler readings close to 12°C. The air stays humid, with relative humidity between 45% and 86% and the peak around 21:00. A lighter breeze peaks around 15:00 near 3.3 km/h.
Expect persistent cloud later on, with amounts around 74% by 12:00. Sunshine remains the exception, not the rule. Views remain open at about 16.1 km. Daylight runs from 06:53 to 19:13, lasting 12 hours 19 minutes of sunlight today.
Taken together, settled sunshine in Mercer Island on September 15, 2026 makes outdoor timing easier, with highs near 19°C.
Frequently asked questions about weather in Mercer Island
How warm does it get in Mercer Island?
The warmest month in Mercer Island is August, with average high temperatures of 25°C. The average temperature during this period is around 19°C.
How cold does it get in Mercer Island?
The coldest month in Mercer Island is February, with average low temperatures of 3°C. The average temperature during this period is around 5°C.
What is the wettest time of year in Mercer Island?
The wettest month in Mercer Island is December, with an average of 204mm of precipitation.
What is the driest time of year in Mercer Island?
The driest month in Mercer Island is July, with an average of 17mm of precipitation.
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