Mercer Island (WA) Weather & Climate: Best Time to Visit
Average temperatures, rainfall, sunshine and the best time to visit Mercer Island.
Climate overview of Mercer Island
Temperatures in Mercer Island, Washington State, United States of America, vary greatly throughout the year. August is the hottest month at 25°C (77°F), while December is the coldest at 8°C (46°F).
The city receives considerable rain/snowfall, with around 1045 mm (41 in) annually. November is the wettest month. It has a distinct dry season from July to August. The most sunshine falls in July, with an average of 10.4 hours of daily sunshine.
Mercer Island Weather by Month
Pick a month to see the average temperature, rainfall and sunshine in Mercer Island — and find the best time to visit.
Monthly Temperature in Mercer Island
The climate in Mercer Island is known for significant temperature differences throughout the year, making the weather dynamic. Typically, average maximum daytime temperatures range from a comfortable 25°C (77°F) in August to a chilly 8°C (46°F) in the coolest month, December.
Nights vary from 14°C (57°F) in August to around 2°C (36°F) during the colder months.
Check out our detailed temperature page for more information.
Temperature ranges by month
Rainfall in Mercer Island
Mercer Island has a notably wet climate with abundant precipitation, recording 1045 mm (41 in) of rain/snowfall per year. The climate in Mercer Island shows significant variation throughout the year. Expect heavy rainfall in November, the wettest month, with an average of 168 mm (6.6 in) of precipitation over 21 rainy days.
In contrast, the driest month July offers drier and sunnier days, with around 15 mm (0.6 in) of rainfall over 4 rainy days. For more details, please visit our Mercer Island Precipitation page.
The mean monthly precipitation over the year, including rain, hail, and snow
The average number of days each month with precipitation
Sunshine Hours in Mercer Island
For those who appreciate different seasons, Mercer Island serves as an ideal destination. Expect longer, more sun-filled days in July with an average of 10.4 hours of sunshine daily, and embrace the darker days in December, offering only 1.8 hours of daily sunlight.
Visit our detailed sunshine hours page for more information.
Monthly hours of sunshine
Daily hours of sunshine
Daily percentage of sunshine
Humidity in Mercer Island by Month
The relative humidity is high throughout the year in Mercer Island.
The city experiences its highest humidity in December, reaching 80%. In July, the humidity drops to its lowest level at 65%. What does this mean? Read our detailed page on humidity levels for further details.
Relative humidity over the year
Wind Speed in Mercer Island
The average wind speed over the year ranges from 4 m/s (8 knots) to 5 m/s (10 knots). It is lower in February, April, May, June, July, August, September, October, November and December and higher in January and March. What does this mean?
The mean monthly wind speed over the year (meters per second)
Best Time to Visit Mercer Island
The wettest months are November, when precipitation is at its highest. Planning your next adventure but unsure where to go? Our climate tool suggests perfect locations tailored to your preferred weather conditions. Discover your ideal travel destination with our weather planner.
Frequently asked questions about the climate in Mercer Island
What is the best time to visit Mercer Island?
June, July, August and September typically offer the most optimal weather in Mercer Island. In contrast, January, February, March, November and December tend to have less optimal conditions. Mercer Island has a distinct dry season from July to August.
What temperatures can I expect in Mercer Island?
Daytime highs range from 8°C (46°F) in December to 25°C (77°F) in August. Nighttime lows range from 2°C (36°F) to 14°C (57°F). Temperatures vary considerably through the year.
How much rain does Mercer Island get?
Annual rainfall is around 1045 mm (41 in). November is the wettest month with 168 mm (6.6 in), while July is the driest with 15 mm (0.6 in).
How sunny is Mercer Island?
Mercer Island receives around 2,171 hours of sunshine per year. July is the sunniest month with 312 hours, while December is the cloudiest with just 54 hours. Overall, Mercer Island enjoys abundant sunshine.
Mercer Island 3-Day Forecast
Mercer Island (WA) 3-Day Forecast
Mercer Island on the map
Mercer Island is highlighted — select any city to see its climate.
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