Washington · NWS SEW office

Mercer Island, WA weather

It is 48°F and cloudy at Boeing Field - King County International Airport as of Oct 28, 2:05 AM PDT. Overnight: Chance Light Rain, low near 48°F, 37% chance of precipitation. Forecast from the National Weather Service, issued Oct 27, 11:27 PM PDT.

Updated Oct 28, 2:27 AM PDT (snapshot)

Current conditions

Temperature

48°F

Cloudy · feels like 43°F

Wind

S 11 mph, gusts 17 mph

Humidity 87% · dew point 45°F

Pressure · visibility

29.85 inHg

Visibility 10 mi

Observed at Boeing Field - King County International Airport (KBFI), Oct 28, 2:05 AM PDT. Station readings can lag or be missing.

Alerts for this area

No active NWS alerts cover the Mercer Island forecast zone right now.

Around the NWS SEW forecast area

No active alerts in zones served by the SEW office near Mercer Island.

From the alert snapshot of Oct 28, 2026, 5:12 AM EDT. Washington has 5 active alerts: see them all.

For official warnings, check weather.gov and your local authorities. OpenForecast repeats National Weather Service alerts and may be delayed or incomplete. Follow instructions from emergency officials.

Next 24 hours

Hourly forecast for Mercer Island (local time)
TimeTempForecastPrecip. chanceWind
Wed 4 AM51°FChance Light Rain26%S 10 mph
Wed 5 AM50°FChance Light Rain34%SSW 9 mph
Wed 6 AM50°FChance Light Rain32%SSW 10 mph
Wed 7 AM50°FChance Light Rain29%S 10 mph
Wed 8 AM49°FChance Light Rain28%S 10 mph
Wed 9 AM49°FSlight Chance Light Rain24%S 9 mph
Wed 10 AM48°FChance Light Rain28%SSW 12 mph
Wed 11 AM49°FChance Light Rain43%SSW 12 mph
Wed 12 PM50°FChance Light Rain46%SSW 12 mph
Wed 1 PM52°FChance Light Rain45%SSW 12 mph
Wed 2 PM52°FChance Showers And Thunderstorms47%SSW 10 mph
Wed 3 PM53°FChance Showers And Thunderstorms49%SSW 10 mph
Wed 4 PM52°FShowers And Thunderstorms Likely56%SSW 12 mph
Wed 5 PM51°FChance Light Rain47%S 7 mph
Wed 6 PM51°FChance Light Rain37%S 7 mph
Wed 7 PM50°FChance Light Rain31%S 8 mph
Wed 8 PM50°FChance Light Rain33%S 5 mph
Wed 9 PM50°FChance Light Rain33%SSE 7 mph
Wed 10 PM49°FSlight Chance Light Rain17%S 7 mph
Wed 11 PM49°FSlight Chance Light Rain22%SSE 6 mph
Thu 12 AM48°FChance Light Rain48%SSE 6 mph
Thu 1 AM48°FLight Rain Likely74%S 6 mph
Thu 2 AM48°FLight Rain Likely67%SSE 6 mph
Thu 3 AM48°FLight Rain Likely60%SE 6 mph

Hourly values come from the NWS gridded forecast for the 2.5 km grid square that covers the city's center point. Conditions elsewhere in Mercer Island can differ.

7-day forecast

Overnight

Low 48°F

A chance of rain. Mostly cloudy. Low around 48, with temperatures rising to around 50 overnight. South southwest wind 9 to 13 mph. Chance of precipitation is 40%. New rainfall amounts less than a tenth of an inch possible.

Wednesday

High 53°F·Low 44°F

A chance of rain before 2pm, then showers and thunderstorms likely between 2pm and 5pm, then a chance of rain. Mostly cloudy. High near 53, with temperatures falling to around 51 in the afternoon. South southwest wind 7 to 12 mph. Chance of precipitation is 60%. New rainfall amounts less than a tenth of an inch possible.

Wednesday Night: Rain likely. Mostly cloudy. Low around 44, with temperatures rising to around 48 overnight. South southeast wind 5 to 8 mph. Chance of precipitation is 70%. New rainfall amounts less than a tenth of an inch possible.

Thursday

High 54°F·Low 43°F

A chance of rain. Partly sunny, with a high near 54. West southwest wind 2 to 6 mph. Chance of precipitation is 40%. New rainfall amounts less than a tenth of an inch possible.

Thursday Night: Rain likely. Mostly cloudy, with a low around 43. East northeast wind around 3 mph. Chance of precipitation is 60%. New rainfall amounts less than a tenth of an inch possible.

Friday

High 52°F·Low 42°F

Rain likely. Partly sunny, with a high near 52. Chance of precipitation is 60%. New rainfall amounts less than a tenth of an inch possible.

Friday Night: A chance of rain before 11pm. Mostly cloudy, with a low around 42.

Saturday

High 53°F·Low 39°F

Partly sunny, with a high near 53.

Saturday Night: Mostly cloudy, with a low around 39.

Sunday

High 54°F·Low 39°F

Partly sunny, with a high near 54.

Sunday Night: Mostly cloudy, with a low around 39.

Monday

High 56°F·Low 42°F

Partly sunny, with a high near 56.

Monday Night: Mostly cloudy, with a low around 42.

Tuesday

High 57°F

Partly sunny, with a high near 57.

Nearby cities

Larger cities in the area

Other cities in King County

See every city we cover in Washington, or check all active alerts.

About this forecast

Forecast office
Mercer Island is served by the National Weather Service SEW forecast office, forecast zone WAZ314, county zone WAC033.
Location used
The Census Bureau's internal point for Mercer Island (47.5640, -122.2312), in King County. Population: 25,302 (2024 estimate), number 45 of the 58 Washington cities on this site.
Radar
Nearest NWS radar: KATX. View it on radar.weather.gov.

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Sources

  • Forecast, hourly forecast, observations and alerts: National Weather Service API, api.weather.gov/points/47.564,-122.2312 (forecast issued Oct 27, 11:27 PM PDT).
  • Official forecast page: forecast.weather.gov.
  • City location and population: U.S. Census Bureau, Vintage 2024 population estimates and 2024 Gazetteer files.
  • Snapshot taken Oct 28, 2026. The NWS and Census Bureau do not endorse OpenForecast.

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