Mercer Island weather in August

In August, Mercer Island sees average daytime highs of 75°F and overnight lows near 58°F, with 1.3 in of rain across 4.8 wet days and about 14.1 hours of daylight. It is the 1st-warmest and 11th-wettest month of the year here.

Highs ease over the month, from about 76°F in the first days to 73°F by the end. The sky is clear or mostly clear about 47% of the time in August, and the air most often feels comfortable.

Daylight stretches from about 14 h 48 min at the start of August to 13 h 18 min by month's end. Set against the rest of the year, August is Mercer Island's 1st-clearest and 11th-windiest month. For the whole year in context, see Mercer Island's year-round climate.

Daytime high
75°
1st warmest
Overnight low
58°
12th coldest
Rainfall
1.3 in
4.8 wet days
Daylight
14 h 06 min
5:10 AM – 7:16 PM
Cloud cover
44%
1st clearest
Wind
4 mph
11th windiest
Solar energy
5.4 kWh/m²
Travel score
8.0
out of 10

Mercer Island is city in King County, Washington State, USA.

Density
738/km²
people per km²
Founded
1960

Air quality: WHO Ambient Air Quality Database. Density & description: Wikidata (CC0), GeoNames.

Temperature in August

Average highAverage lowShaded bands: 10–90% of days

Highs ease over the month, from about 76°F in the first days to 73°F by the end.

A typical August day in Mercer Island reaches about 75°F in the afternoon and slips back to 58°F overnight — a 17°F spread between the day's warmth and the night's chill. On most days the high lands between 67°F and 83°F. Set against its neighbours, August runs on par with July and about 6°F warmer than September.

50°60°70°80°151015202531
Avg high (°F)Avg low (°F)
17658
27658
37658
47658
57658
67658
77658
87658
97658
107658
117658
127658
137658
147558
157558
167558
177558
187558
197558
207458
217457
227457
237457
247457
257457
267457
277357
287356
297356
307356
317356

Mercer Island weather by month

How August compares with the rest of the year at a glance. August is the 1st-warmest and 11th-wettest month here — the current month is highlighted below.

MonthHigh / Low (°F)Rainfall (inches)Wet daysSnow daysDaylight (hours)Travel score
Jan46° / 38°6.918.42.28.71.0
Feb49° / 39°4.714.51.89.91.6
Mar52° / 40°5.517.50.811.62.3
Apr57° / 44°4.514.90.113.33.5
May64° / 49°3.012014.95.3
Jun68° / 53°2.39.5015.76.3
Jul74° / 57°1.05015.47.9
Aug75° / 58°1.34.8014.18.0
Sep69° / 53°2.68.4012.46.8
Oct59° / 47°5.314.1010.64.2
Nov50° / 42°7.6180.69.11.9
Dec45° / 38°7.017.62.18.30.8

Cloud cover in August

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 47% of the time in August, the clearest month of the year.

Beyond those clear spells, partly cloudy skies cover about 17% of August, with mostly cloudy or overcast conditions the remaining 36%. Skies tend to cloud over as the month goes on.

0%25%50%75%100%151015202531
Clearer (%)Cloudier (%)
17129
26931
36931
46931
56832
66832
76634
86634
96634
106535
116436
126436
136436
146337
156337
166337
176337
186337
196337
206337
216238
226238
236238
246238
256238
266139
276139
286040
296040
306139
316040

Chance of precipitation in August

Any precipitation

Mercer Island gets around 1.3 in of rain over 4.8 wet days in August. The line is the day-by-day chance of measurable precipitation.

Day to day, the chance of measurable rain averages around 15% and peaks near 23% on the wettest days. The odds climb toward the end of the month.

0%10%20%30%151015202531
Rain chance (%)
110
210
311
411
511
611
712
812
913
1013
1113
1214
1314
1414
1514
1615
1715
1815
1916
2016
2117
2217
2318
2418
2519
2620
2720
2821
2921
3022
3123

Humidity in August

DryComfortableHumidMuggyOppressiveMiserable

Most of August feels comfortable — the stacked bands show each day's mix of comfort levels, read off the dew point.

By dew point, August lands in the comfortable band about 49% of days. It rarely turns muggy — the humid and sticky bands barely register.

0%25%50%75%100%151015202531
Dry (%)Comfortable (%)Humid (%)
139538
238548
338548
438548
537558
637558
737558
836559
936559
1036559
1136559
1236559
1336559
1437549
1538539
1639529
1741509
1842498
1944488
2045478
2147467
2248457
2349456
2450446
2552435
2653425
2754424
2855414
2957403
3057403
3158393

Wind in August

Winds average 4 mph in August.

Across August, daily wind ranges from about 4 mph on the calmest days to 4 mph at its breeziest. It stays fairly steady from day to day.

0246810151015202531
Wind speed (mph)Feels
14calm
24calm
34calm
44calm
54calm
64calm
74calm
84calm
94calm
104calm
114calm
124calm
134calm
144calm
154calm
164calm
174calm
184calm
194calm
204calm
214calm
224calm
234calm
244calm
254calm
264calm
274calm
284calm
294calm
304calm
314calm

Sunrise & sunset in August

DaylightNight

Daylight runs from about 14 h 48 min at the start of August to 13 h 18 min by month's end. The lit band spans sunrise to sunset each day.

Days shrink by about 90 minutes over August. Sunrise moves from 4:50 AM to 5:31 AM, and sunset from 7:39 PM to 6:47 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202531
Daylight (h)Sunrise (AM)Sunset (PM)
114.84:507:39
214.84:527:38
314.74:537:37
414.74:547:35
514.64:567:34
614.64:577:32
714.54:587:31
814.55:007:29
914.45:017:27
1014.45:027:26
1114.35:047:24
1214.35:057:23
1314.25:067:21
1414.25:087:19
1514.15:097:17
1614.15:107:16
1714.05:127:14
1814.05:137:12
1913.95:147:10
2013.95:167:08
2113.85:177:06
2213.85:197:05
2313.75:207:03
2413.75:217:01
2513.65:236:59
2613.55:246:57
2713.55:256:55
2813.45:276:53
2913.45:286:51
3013.35:306:49
3113.35:316:47

Solar energy in August

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in August, about 5.4 kWh/m².

For context, solar energy here swings from a low near 0.88 kWh/m² to a high of 6.14 kWh/m² in July across the year — August's 5.4 kWh/m² sits near the top of that range.

0246151015202531
Solar energy (kWh/m²)Level
16.1Intense
26.0Intense
36.0Intense
46.0Bright
55.9Bright
65.9Bright
75.8Bright
85.8Bright
95.7Bright
105.7Bright
115.7Bright
125.6Bright
135.6Bright
145.5Bright
155.5Bright
165.4Bright
175.4Bright
185.3Bright
195.3Bright
205.3Bright
215.2Bright
225.2Bright
235.1Bright
245.0Bright
255.0Bright
265.0Bright
274.9Bright
284.9Bright
294.8Bright
304.8Bright
314.7Bright
Planning a trip in August

Hazard calendar for Mercer Island

In seasonPeak

None of Mercer Island's seasonal hazards are active in August. The full-year calendar below shows when the rainy season, cyclone risk and dust haze do peak.

Mercer Island's rainy season runs October–April, when most of the year's rain falls.

Rainy season
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec

Is August a good time to visit Mercer Island?

Our two travel scores rate August for general sightseeing and for beach or pool weather — 0 (poor) to 10 (ideal).

8.0
Sightseeing
1st-best month of the year
6.7
Beach & pool
1st-best month of the year

August is one of the better times to visit Mercer Island for general sightseeing. The water and warmth also suit a beach or pool day.

What to pack for Mercer Island in August

From August's temperature range, rain chance, sun and wind — what's worth putting in the bag.

In August, Mercer Island sees daytime highs around 75°F and nights near 58°F. Worth packing: light clothes and sun protection. About 5 days see rain.

light clothessun protection

UV index in Mercer Island in August

LowModerateHighVery highExtreme

Clear-sky midday UV in August peaks around 6 — enough to warrant sun protection. The full-year curve, shaded by WHO exposure level, is below.

Under clear skies, the midday UV index in Mercer Island peaks around July 17 at about 8 (very high) — sunscreen and a hat are worth it in the middle of the day. It bottoms out near December 18 at about 1 (low).

The index reaches 3 or more — the level where the WHO recommends sun protection — in 7 months of the year.

025710JanFebMarAprMayJunJulAugSepOctNovDecLowModerateHighVery highHighModerateLowJul 17UV 8Dec 18UV 1
UV index (midday)Level
Jan1Low
Feb1Low
Mar4Moderate
Apr5Moderate
May7High
Jun6High
Jul8Very high
Aug6High
Sep4Moderate
Oct3Moderate
Nov1Low
Dec1Low

Air quality in Mercer Island in August

GoodModeratePoorUnhealthyVery unhealthy

Average fine-particle pollution (PM2.5) through the year — so you can see where August falls, not just the annual average.

Air quality in Mercer Island is worst in September — around 22 µg/m³ PM2.5 (moderate), about 3.4× the cleanest month (December, 7 µg/m³).

Modeled monthly averages (CAMS reanalysis, 2015–2024).

0102030JanFebMarAprMayJunJulAugSepOctNovDecGoodGoodModerateGoodSep 1322 µg/m³Dec 177 µg/m³
PM2.5 (µg/m³)Level
Jan8Good
Feb9Good
Mar12Moderate
Apr12Good
May11Good
Jun10Good
Jul10Good
Aug18Moderate
Sep22Moderate
Oct12Good
Nov8Good
Dec7Good
Location & terrain

Where is Mercer Island?

Mercer Island sits at 47.6°N, 122.2°W, 335 ft above sea level, in United States. The nearest listed city is Columbia City, 2.5 mi away.

Topography around Mercer Island

How much the land rises and falls, and what covers it, within 2, 10 and 50 miles of Mercer Island.

Within 2 miles, the terrain around Mercer Island has only modest variations in elevation — a maximum elevation change of 400 ft around an average of 105 ft above sea level; within 10 miles, large variations in elevation — a maximum elevation change of 2,037 ft; within 50 miles, extreme variations in elevation — a maximum elevation change of 8,179 ft.

The land around Mercer Island is covered by trees (46%) and water (43%) within 2 miles, trees (48%), artificial surfaces (27%) and water (20%) within 10 miles, and trees (75%) within 50 miles.

2 miles
400 ft
10 miles
2,037 ft
50 miles
8,179 ft
treesgrasslandartificial surfacesbare terrainwater
August weather nearby: Columbia City 2.5 mi · Bellevue 3.1 mi · Bryn Mawr-Skyway 5.6 mi · West Lake Sammamish 5.6 mi · Seattle 5.6 mi · Renton 6.2 mi · Tukwila 6.8 mi · Kirkland 7.5 mi

United States travel facts

Power plugs
Type A / B
120 V · 60 Hz
Prices
≈ 100% of US
price level, 2025
GDP per capita
$90,027
2025
Happiness
6.8 / 10
World Happiness, 2025
Safe drinking water
98%
of population, 2024
Homicide rate
5.8
per 100k, 2023
Road deaths
12.7
per 100k/yr, 2019
Income group
High
World Bank
Religion
Protestant 47%unaffiliated 23%Roman Catholic 21%Jewish 2%

Sources: World Bank, US State Department, World Happiness Report, WHO/UNICEF, EF EPI, CIA World Factbook.

Data sources

Temperature, precipitation, cloud, humidity, wind and solar figures are a 1991–2020 climatology for Mercer Island (47.5707°, -122.2221°, elevation 335 ft), computed from hourly ERA5 reanalysis — contains modified Copernicus Climate Change Service information. Sun figures are astronomical calculations, not observations. City data © GeoNames, CC BY 4.0. Map outlines from Natural Earth (public domain); interactive map © Google. UV index is derived from CAMS (Copernicus Atmosphere Monitoring Service) clear-sky UV data — contains modified Copernicus Atmosphere Monitoring Service information. Monthly air-quality (PM2.5) seasonality is from the CAMS EAC4 reanalysis (Copernicus Atmosphere Monitoring Service), scaled to the WHO annual mean where available. Topography is sampled from the Copernicus DEM GLO-90 elevation model (© ESA/Airbus) and ESA WorldCover 2021 land cover (CC BY 4.0).