St. Thomas weather in September

In September, St. Thomas sees average daytime highs of 21°C and overnight lows near 14°C, with 84 mm of rain across 9.4 wet days and about 12.3 hours of daylight. It is the 4th-warmest and 6th-wettest month of the year here.

Highs ease over the month, from about 23°C in the first days to 18°C by the end. The sky is clear or mostly clear about 39% of the time in September, and the air most often feels dry.

Daylight stretches from about 13 hours at the start of September to 11 h 36 min by month's end. Set against the rest of the year, September is St. Thomas's 2nd-clearest and 9th-windiest month. For the whole year in context, see St. Thomas's year-round climate.

Daytime high
21°
4th warmest
Overnight low
14°
9th coldest
Rainfall
84 mm
9.4 wet days
Daylight
12 h 18 min
6:10 AM – 6:28 PM
Cloud cover
53%
2nd clearest
Wind
15 km/h
9th windiest
Solar energy
4.41 kWh/m²
Travel score
6.6
out of 10

Temperature in September

Average highAverage lowShaded bands: 10–90% of days

Highs ease over the month, from about 23°C in the first days to 18°C by the end.

A typical September day in St. Thomas reaches about 21°C in the afternoon and slips back to 14°C overnight — a 7°C spread between the day's warmth and the night's chill. On most days the high lands between 16°C and 25°C. Set against its neighbours, September runs about 4°C cooler than August and about 7°C warmer than October.

10°15°20°25°30°151015202530
Avg high (°C)Avg low (°C)
12317
22317
32317
42316
52316
62316
72316
82216
92216
102215
112215
122215
132115
142115
152114
162114
172114
182114
192014
202013
212013
222013
231913
241913
251912
261912
271812
281812
291812
301811

How September really feels in St. Thomas

Once humidity and wind are folded in, September 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

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

St. Thomas weather by month

How September compares with the rest of the year at a glance. September is the 4th-warmest and 6th-wettest month here — the current month is highlighted below.

MonthHigh / Low (°C)Rainfall (mm)Wet daysSnow daysDaylight (hours)Travel score
Jan-1° / -7°7511.58.39.20.0
Feb-1° / -7°589.4710.30.0
Mar / -3°7310.34.911.60.1
Apr10° / 9511.71.713.12.1
May17° / 10°9412.1014.45.1
Jun23° / 16°9911.7015.16.6
Jul25° / 19°9612014.86.6
Aug25° / 18°8210.2013.77.0
Sep21° / 14°849.4012.36.6
Oct14° / 8611.50.110.84.0
Nov / 8110.82.69.61.0
Dec / -3°7411.57.18.90.0

Cloud cover in September

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 39% of the time in September.

Beyond those clear spells, partly cloudy skies cover about 16% of September, with mostly cloudy or overcast conditions the remaining 45%.

0%25%50%75%100%151015202530
Clearer (%)Cloudier (%)
15842
25842
35842
45842
55842
65743
75842
85842
95743
105743
115644
125743
135644
145644
155545
165545
175545
185545
195545
205545
215545
225446
235446
245347
255347
265248
275149
285149
295149
305149

Chance of precipitation in September

Any precipitation

St. Thomas gets around 84 mm of rain over 9.4 wet days in September. The line is the day-by-day chance of measurable precipitation.

Day to day, the chance of measurable rain averages around 32% and peaks near 36% on the wettest days.

0%10%20%30%40%50%151015202530
Rain chance (%)
130
231
331
431
531
631
731
831
931
1031
1131
1231
1331
1430
1530
1630
1730
1830
1930
2030
2130
2231
2332
2433
2534
2635
2736
2836
2936
3036

Humidity in September

DryComfortableHumidMuggyOppressiveMiserable

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

By dew point, September lands in the dry band about 47% of days. Sticky, muggy-or-worse air turns up on roughly 12% of them.

0%25%50%75%100%151015202530
Dry (%)Comfortable (%)Humid (%)Muggy (%)Oppressive (%)
1252723214
2262722204
3272722204
4292721194
5302721183
6322721173
7342721163
8352621162
9372621152
10382521142
11402521132
12412421131
13432321121
14452320111
15462220101
16482220101
1749221991
1851211990
1953211880
2054211780
2156211670
2259201560
2360201460
2461201450
2562201350
2664201240
2765201140
2866201040
296720940
306919930

Wind in September

Winds average 15 km/h in September.

Across September, daily wind ranges from about 14 km/h on the calmest days to 17 km/h at its breeziest. It stays fairly steady from day to day.

05101520151015202530
Wind speed (km/h)Feels
114light breeze
214light breeze
314light breeze
414light breeze
514light breeze
614light breeze
715light breeze
815light breeze
915light breeze
1015light breeze
1115light breeze
1215light breeze
1315light breeze
1415light breeze
1515light breeze
1615light breeze
1715light breeze
1815light breeze
1915light breeze
2015light breeze
2116light breeze
2216light breeze
2316light breeze
2416light breeze
2516light breeze
2616light breeze
2716light breeze
2816light breeze
2916light breeze
3017light breeze

Sunrise & sunset in September

DaylightNight

Daylight runs from about 13 hours at the start of September to 11 h 36 min by month's end. The lit band spans sunrise to sunset each day.

Days shrink by about 84 minutes over September. Sunrise moves from 5:54 AM to 6:26 AM, and sunset from 6:55 PM to 6:02 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202530
Daylight (h)Sunrise (AM)Sunset (PM)
113.05:546:55
213.05:556:53
312.95:566:51
412.95:576:50
512.85:586:48
612.85:596:46
712.76:006:44
812.76:026:42
912.66:036:41
1012.66:046:39
1112.56:056:37
1212.56:066:35
1312.46:076:33
1412.46:086:31
1512.36:096:29
1612.36:106:28
1712.26:126:26
1812.26:136:24
1912.16:146:22
2012.16:156:20
2112.06:166:18
2212.06:176:16
2311.96:186:15
2411.96:196:13
2511.86:216:11
2611.86:226:09
2711.76:236:07
2811.76:246:05
2911.66:256:04
3011.66:266:02

Solar energy in September

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in September, about 4.41 kWh/m².

For context, solar energy here swings from a low near 1.34 kWh/m² to a high of 6.64 kWh/m² in June across the year — September's 4.41 kWh/m² falls in the middle.

0246151015202530
Solar energy (kWh/m²)Level
15.0Bright
25.0Bright
35.0Bright
44.9Bright
54.9Bright
64.8Bright
74.8Bright
84.7Bright
94.7Bright
104.6Bright
114.6Bright
124.5Bright
134.5Bright
144.5Bright
154.4Bright
164.4Bright
174.3Bright
184.3Bright
194.3Bright
204.2Bright
214.2Bright
224.1Bright
234.1Bright
244.0Bright
254.0Moderate
263.9Moderate
273.9Moderate
283.8Moderate
293.8Moderate
303.7Moderate
Planning a trip in September

Is September a good time to visit St. Thomas?

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

6.6
Sightseeing
2nd-best month of the year
3.9
Beach & pool
4th-best month of the year

September is a reasonable time to visit St. Thomas for sightseeing.

What to pack for St. Thomas in September

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

In September, St. Thomas sees daytime highs around 21°C and nights near 14°C. Worth packing: rain gear. About 9 days see rain.

rain gear

Sea temperature near St. Thomas in September

The nearest coast averages about 21°C in September — the other half of the beach question. The full-year curve and swim-comfort zones are below.

The sea at the nearest coast (about 17 km away) is warmest in August at about 23°C and coldest in February near 1°C.

It's comfortable for a long swim from Jul 5 to Sep 20 — about 2.6 months when the water holds above 20°C.

0°10°20°JanFebMarAprMayJunJulAugSepOctNovDecbracingcoolrefreshingwarmtropicalcomfortable to swim
Sea temperature (°C)Comfort
Jan2Bracing
Feb1Bracing
Mar1Bracing
Apr4Bracing
May10Bracing
Jun17Cool
Jul22Refreshing
Aug23Refreshing
Sep21Refreshing
Oct16Cool
Nov10Bracing
Dec5Bracing

UV index in St. Thomas in September

LowModerateHighVery highExtreme

Clear-sky midday UV in September 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 St. Thomas peaks around June 23 at about 9 (very high) — sunscreen, a hat and midday shade are essential. It bottoms out near January 1 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 23UV 9Jan 1UV 1
UV index (midday)Level
Jan1Low
Feb2Moderate
Mar4Moderate
Apr5High
May7High
Jun9Very high
Jul9Very high
Aug7High
Sep6High
Oct3Moderate
Nov2Low
Dec1Low
Location & terrain

Where is St. Thomas?

St. Thomas sits at 42.8°N, 81.2°W, 232 m above sea level, in Canada. The nearest listed city is London, 24 km away.

Topography around St. Thomas

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

Within 3 km, the terrain around St. Thomas has only modest variations in elevation — a maximum elevation change of 65 m around an average of 233 m above sea level; within 16 km, only modest variations in elevation — a maximum elevation change of 125 m; within 80 km, significant variations in elevation — a maximum elevation change of 251 m.

The land around St. Thomas is covered by trees (35%) and artificial surfaces (33%) within 3 km, cropland (60%) and trees (20%) within 16 km, and cropland (49%) and water (33%) within 80 km.

3 km
65 m
16 km
125 m
80 km
251 m
treesgrasslandcroplandartificial surfacesbare terrainwater
September weather nearby: London 24 km · Tillsonburg 38 km · Strathroy 41 km · Woodstock 53 km · Norfolk County 65 km · Stratford 69 km · Brant 79 km · Brantford 84 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 St. Thomas (42.7736°, -81.1804°, elevation 232 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).