Sarnia weather in August

In August, Sarnia sees average daytime highs of 25°C and overnight lows near 18°C, with 70 mm of rain across 10.4 wet days and about 13.8 hours of daylight. It is the 2nd-warmest and 7th-wettest month of the year here.

Day-to-day highs hold fairly steady near 25°C through the month. The sky is clear or mostly clear about 33% of the time in August, and the air most often feels humid.

Daylight stretches from about 14 h 24 min at the start of August to 13 h 06 min by month's end. Set against the rest of the year, August is Sarnia's 2nd-clearest and 12th-windiest month. For the whole year in context, see Sarnia's year-round climate.

Daytime high
25°
2nd warmest
Overnight low
18°
11th coldest
Rainfall
70 mm
10.4 wet days
Daylight
13 h 48 min
5:41 AM – 7:27 PM
Cloud cover
55%
2nd clearest
Wind
11 km/h
12th windiest
Solar energy
5.33 kWh/m²
Travel score
6.9
out of 10

Sarnia is city in Ontario, Canada.

Air quality
Good
PM2.5 7 µg/m³ · 2019
Density
440/km²
people per km²
Founded
1830

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

Temperature in August

Average highAverage lowShaded bands: 10–90% of days

Day-to-day highs hold fairly steady near 25°C through the month.

A typical August day in Sarnia reaches about 25°C in the afternoon and slips back to 18°C overnight — a 7°C spread between the day's warmth and the night's chill. On most days the high lands between 21°C and 29°C. Set against its neighbours, August runs about 1°C cooler than July and about 4°C warmer than September.

10°15°20°25°30°151015202531
Avg high (°C)Avg low (°C)
12619
22618
32618
42618
52618
62618
72618
82518
92518
102518
112518
122518
132518
142518
152518
162518
172518
182518
192518
202518
212517
222517
232517
242517
252517
262517
272517
282417
292417
302417
312417

How August really feels in Sarnia

Once humidity and wind are folded in, August averages 0 days that feel above 32°C and 0 that feel at or below 0°C — the comfort signal a plain temperature reading hides.

Days feeling ≥ 32°C
0
heat index over the day's high
Days feeling ≤ C
0
wind chill below the day's low

August sits comfortably in between — no days that feel dangerously hot or drop to a hard freeze once humidity and wind are folded in.

Sarnia weather by month

How August compares with the rest of the year at a glance. August is the 2nd-warmest and 7th-wettest month here — the current month is highlighted below.

MonthHigh / Low (°C)Rainfall (mm)Wet daysSnow daysDaylight (hours)Travel score
Jan-1° / -7°579.67.39.20.0
Feb / -7°518.46.310.20.0
Mar / -3°579.64.611.60.3
Apr11° / 8511.41.813.12.7
May18° / 10°8512014.45.4
Jun24° / 16°8710.8015.16.7
Jul26° / 18°7111014.86.6
Aug25° / 18°7010.4013.86.9
Sep21° / 14°739.1012.36.7
Oct15° / 7710.80.110.84.3
Nov / 669.72.49.51.2
Dec / -3°569.45.68.90.0

Cloud cover in August

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 33% of the time in August.

Beyond those clear spells, partly cloudy skies cover about 22% of August, with mostly cloudy or overcast conditions the remaining 45%.

0%25%50%75%100%151015202531
Clearer (%)Cloudier (%)
15743
25743
35743
45743
55743
65644
75644
85644
95545
105545
115545
125545
135545
145545
155545
165545
175545
185545
195446
205545
215545
225446
235545
245545
255545
265545
275644
285545
295545
305545
315644

Chance of precipitation in August

Any precipitation

Sarnia gets around 70 mm of rain over 10.4 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 34% and peaks near 37% on the wettest days. The odds ease toward the end of the month.

0%10%20%30%40%50%151015202531
Rain chance (%)
137
237
337
437
537
637
737
836
936
1036
1136
1236
1335
1435
1535
1634
1734
1833
1933
2033
2132
2232
2331
2430
2530
2629
2729
2829
2929
3029
3129

Humidity in August

DryComfortableHumidMuggyOppressiveMiserable

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

By dew point, August lands in the humid band about 28% of days. Sticky, muggy-or-worse air turns up on roughly 32% of them.

0%25%50%75%100%151015202531
Dry (%)Comfortable (%)Humid (%)Muggy (%)Oppressive (%)
192630278
292630278
392630278
492630278
5102630277
6102630277
7102629277
8112629277
9112629277
10122728277
11122728276
12122728276
13132827276
14132827275
15132827275
16132827275
17132827274
18132827274
19142827274
20142827274
21142827274
22142827274
23142827274
24152827264
25152827264
26162827254
27162827244
28172827244
29182827234
30192827224
31202926214

Wind in August

Winds average 11 km/h in August, the calmest month.

Across August, daily wind ranges from about 11 km/h on the calmest days to 12 km/h at its breeziest. It stays fairly steady from day to day.

051015151015202531
Wind speed (km/h)Feels
111calm
211calm
311calm
411calm
511calm
611calm
711calm
811calm
911calm
1011calm
1111calm
1211calm
1311calm
1411calm
1511calm
1611calm
1711calm
1811calm
1911calm
2011calm
2112calm
2212calm
2312calm
2412calm
2512calm
2612calm
2712calm
2812calm
2912calm
3012calm
3112calm

Sunrise & sunset in August

DaylightNight

Daylight runs from about 14 h 24 min at the start of August to 13 h 06 min by month's end. The lit band spans sunrise to sunset each day.

Days shrink by about 78 minutes over August. Sunrise moves from 5:24 AM to 5:57 AM, and sunset from 7:47 PM to 7:02 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202531
Daylight (h)Sunrise (AM)Sunset (PM)
114.45:247:47
214.35:257:46
314.35:267:45
414.35:277:44
514.25:287:42
614.25:307:41
714.25:317:40
814.15:327:38
914.15:337:37
1014.05:347:36
1114.05:357:34
1213.95:367:33
1313.95:377:31
1413.95:387:30
1513.85:397:28
1613.85:417:27
1713.75:427:25
1813.75:437:24
1913.65:447:22
2013.65:457:21
2113.55:467:19
2213.55:477:17
2313.55:487:16
2413.45:507:14
2513.45:517:12
2613.35:527:11
2713.35:537:09
2813.25:547:07
2913.25:557:05
3013.15:567:04
3113.15:577:02

Solar energy in August

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in August, about 5.33 kWh/m².

For context, solar energy here swings from a low near 1.36 kWh/m² to a high of 6.37 kWh/m² in June across the year — August's 5.33 kWh/m² falls in the middle.

0246151015202531
Solar energy (kWh/m²)Level
15.8Bright
25.8Bright
35.8Bright
45.7Bright
55.7Bright
65.7Bright
75.6Bright
85.6Bright
95.6Bright
105.5Bright
115.5Bright
125.5Bright
135.4Bright
145.4Bright
155.4Bright
165.3Bright
175.3Bright
185.3Bright
195.2Bright
205.2Bright
215.2Bright
225.1Bright
235.1Bright
245.1Bright
255.0Bright
265.0Bright
275.0Bright
284.9Bright
294.9Bright
304.9Bright
314.8Bright
Planning a trip in August

Is August a good time to visit Sarnia?

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

6.9
Sightseeing
1st-best month of the year
6.2
Beach & pool
2nd-best month of the year

August is a reasonable time to visit Sarnia for sightseeing. The water and warmth also suit a beach or pool day.

What to pack for Sarnia in August

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

In August, Sarnia sees daytime highs around 25°C and nights near 18°C. Worth packing: light clothes, rain gear and sun protection. About 10 days see rain.

light clothesrain gearsun protection

Sea temperature near Sarnia in August

The nearest coast averages about 22°C in August — the other half of the beach question. The full-year curve and swim-comfort zones are below.

The sea at the nearest coast (about 16 km away) is warmest in August at about 22°C and coldest in February near 1°C.

It's comfortable for a long swim from Jul 19 to Sep 8 — about 1.7 months when the water holds above 20°C.

0°10°20°JanFebMarAprMayJunJulAugSepOctNovDecbracingcoolrefreshingwarmcomfortable to swim
Sea temperature (°C)Comfort
Jan2Bracing
Feb1Bracing
Mar1Bracing
Apr3Bracing
May7Bracing
Jun14Bracing
Jul20Refreshing
Aug22Refreshing
Sep20Cool
Oct14Bracing
Nov9Bracing
Dec5Bracing

UV index in Sarnia in August

LowModerateHighVery highExtreme

Clear-sky midday UV in August peaks around 7 — enough to warrant sun protection. The full-year curve, shaded by WHO exposure level, is below.

Under clear skies, the midday UV index in Sarnia peaks around June 20 at about 9 (very high) — sunscreen, a hat and midday shade are essential. It bottoms out near December 20 at about 1 (low).

The index reaches 3 or more — the level where the WHO recommends sun protection — in 8 months of the year.

025710JanFebMarAprMayJunJulAugSepOctNovDecLowModerateHighVery highHighModerateLowJun 20UV 9Dec 20UV 1
UV index (midday)Level
Jan2Low
Feb2Moderate
Mar4Moderate
Apr5High
May7High
Jun9Very high
Jul8Very high
Aug7High
Sep6High
Oct3Moderate
Nov2Moderate
Dec1Low
Location & terrain

Where is Sarnia?

Sarnia sits at 43.0°N, 82.4°W, 185 m above sea level, in Canada. The nearest listed city is Port Huron, 2.0 km away.

Topography around Sarnia

How much the land rises and falls, and what covers it, within 3, 16 and 80 km of Sarnia.

Within 3 km, the terrain around Sarnia has only modest variations in elevation — a maximum elevation change of 19 m around an average of 182 m above sea level; within 16 km, only modest variations in elevation — a maximum elevation change of 69 m; within 80 km, only modest variations in elevation — a maximum elevation change of 216 m.

The land around Sarnia is covered by artificial surfaces (52%) and trees (22%) within 3 km, cropland (27%), trees (25%) and water (24%) within 16 km, and cropland (45%) and water (25%) within 80 km.

3 km
19 m
16 km
69 m
80 km
216 m
treesgrasslandcroplandartificial surfacesbare terrainwaterwetland
August weather nearby: Port Huron 2.0 km · Mount Clemens 57 km · Clinton Township 61 km · Shelby 62 km · Strathroy 64 km · Chatham 65 km · Saint Clair Shores 67 km · Sterling Heights 68 km

Canada travel facts

Travel advisory
Level 1
Exercise Normal Precautions
Power plugs
Type A / B
120 V · 60 Hz
Prices
≈ 83% of US
price level, 2025
GDP per capita
$55,698
2025
Happiness
6.7 / 10
World Happiness, 2025
Safe drinking water
97%
of population, 2024
Homicide rate
2
per 100k, 2023
Road deaths
5.3
per 100k/yr, 2019
Income group
High
World Bank
Religion
Christian 53%none 35%Muslim 5%Hindu 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 Sarnia (42.9787°, -82.4041°, elevation 185 m), 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. Sea temperatures are the NOAA OISST v2.1 1991–2020 monthly climatology (public domain), sampled at the nearest ocean point. UV index is derived from CAMS (Copernicus Atmosphere Monitoring Service) clear-sky UV data — contains modified Copernicus Atmosphere Monitoring Service information. Topography is sampled from the Copernicus DEM GLO-90 elevation model (© ESA/Airbus) and ESA WorldCover 2021 land cover (CC BY 4.0).