Castries weather in September

In September, Castries sees average daytime highs of 30°C and overnight lows near 26°C, with 104 mm of rain across 19.4 wet days and about 12.1 hours of daylight. It is the 1st-warmest and 2nd-wettest month of the year here.

Day-to-day highs hold fairly steady near 30°C through the month. The sky is clear or mostly clear about 29% of the time in September, and the air most often feels oppressive.

Daylight stretches from about 12 h 18 min at the start of September to 11 h 54 min by month's end. Set against the rest of the year, September is Castries's 12th-clearest and 12th-windiest month. For the whole year in context, see Castries's year-round climate.

Daytime high
30°
1st warmest
Overnight low
26°
12th coldest
Rainfall
104 mm
19.4 wet days
Daylight
12 h 06 min
5:56 AM – 6:01 PM
Cloud cover
65%
12th clearest
Wind
16 km/h
12th windiest
Solar energy
5.95 kWh/m²
Travel score
3.9
out of 10

Castries is capital of Saint Lucia.

Density
253/km²
people per km²
Founded
1650

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

Temperature in September

Average highAverage lowShaded bands: 10–90% of days

Day-to-day highs hold fairly steady near 30°C through the month.

A typical September day in Castries reaches about 30°C in the afternoon and slips back to 26°C overnight — a 4°C spread between the day's warmth and the night's chill. On most days the high lands between 28°C and 31°C. Set against its neighbours, September runs on par with August and on par with October.

20°25°30°35°151015202530
Avg high (°C)Avg low (°C)
13026
23026
33026
43026
53026
63026
73026
83026
93026
103026
113026
123026
133026
143026
153026
163026
173026
183026
193026
203026
213026
223026
233026
243026
253026
263026
273026
283026
293026
303026

How September really feels in Castries

Once humidity and wind are folded in, September averages 30 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
30
heat index over the day's high
Days feeling ≤ C
0
wind chill below the day's low

The story in September is heat — humidity pushes the afternoon "feels like" well above the raw temperature.

Castries weather by month

How September compares with the rest of the year at a glance. September is the 1st-warmest and 2nd-wettest month here — the current month is highlighted below.

MonthHigh / Low (°C)Rainfall (mm)Wet daysDaylight (hours)Travel score
Jan28° / 24°3111.811.36.5
Feb28° / 24°218.811.56.7
Mar28° / 24°269.811.96.1
Apr29° / 25°3611.512.35.4
May29° / 25°4712.512.64.9
Jun29° / 25°6515.112.84.5
Jul29° / 25°8320.312.74.2
Aug30° / 26°9920.712.54.0
Sep30° / 26°10419.412.13.9
Oct29° / 25°11920.911.74.0
Nov29° / 25°10218.911.44.5
Dec28° / 25°421311.25.7

Cloud cover in September

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 29% of the time in September, the cloudiest month of the year.

Beyond those clear spells, partly cloudy skies cover about 16% of September, with mostly cloudy or overcast conditions the remaining 55%. Skies tend to cloud over as the month goes on.

0%25%50%75%100%151015202530
Clearer (%)Cloudier (%)
15347
25347
35248
45248
55050
65050
75050
84951
94852
104753
114753
124555
134456
144456
154357
164258
174159
184159
194159
204159
214159
224159
234159
244159
254258
264159
274159
284159
294159
304060

Chance of precipitation in September

Any precipitation

Castries gets around 104 mm of rain over 19.4 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 64% and peaks near 68% on the wettest days.

0%20%40%60%80%151015202530
Rain chance (%)
162
262
361
461
562
662
762
863
963
1063
1163
1263
1363
1463
1563
1664
1764
1864
1965
2065
2165
2265
2365
2466
2566
2666
2767
2867
2968
3068

Humidity in September

DryComfortableHumidMuggyOppressiveMiserable

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

By dew point, September lands in the oppressive band about 85% of days. Sticky, muggy-or-worse air turns up on roughly 100% of them.

0%25%50%75%100%151015202530
Muggy (%)Oppressive (%)Miserable (%)
108515
208515
308515
408515
508416
608416
708416
808416
908416
1008416
1108416
1208416
1318316
1418316
1518316
1618316
1718415
1818415
1918415
2018514
2118514
2218514
2318613
2418613
2518613
2618613
2718613
2818712
2918712
3018712

Wind in September

Winds average 16 km/h in September, the calmest month.

Across September, daily wind ranges from about 16 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
117light breeze
216light breeze
316light breeze
416light breeze
516light breeze
616light breeze
716light breeze
816light breeze
916light breeze
1016light breeze
1116light breeze
1216light breeze
1316light breeze
1416light breeze
1516light breeze
1616light breeze
1716light breeze
1816light breeze
1916light breeze
2016light breeze
2116light breeze
2216light breeze
2316light breeze
2416light breeze
2516light breeze
2616light breeze
2716light breeze
2816light breeze
2916light breeze
3016light breeze

Sunrise & sunset in September

DaylightNight

Daylight runs from about 12 h 18 min at the start of September to 11 h 54 min by month's end. The lit band spans sunrise to sunset each day.

Days shrink by about 24 minutes over September. Sunrise moves from 5:56 AM to 5:57 AM, and sunset from 6:12 PM to 5:50 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202530
Daylight (h)Sunrise (AM)Sunset (PM)
112.35:566:12
212.35:566:11
312.25:566:11
412.25:566:10
512.25:566:09
612.25:566:08
712.25:566:08
812.25:566:07
912.25:566:06
1012.25:566:05
1112.15:566:05
1212.15:566:04
1312.15:566:03
1412.15:566:02
1512.15:566:01
1612.15:566:01
1712.15:566:00
1812.15:565:59
1912.05:565:58
2012.05:565:58
2112.05:565:57
2212.05:565:56
2312.05:565:55
2412.05:565:55
2512.05:565:54
2611.95:565:53
2711.95:565:52
2811.95:575:51
2911.95:575:51
3011.95:575:50

Solar energy in September

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in September, about 5.95 kWh/m².

For context, solar energy here swings from a low near 4.95 kWh/m² to a high of 6.65 kWh/m² in April across the year — September's 5.95 kWh/m² falls in the middle.

0246151015202530
Solar energy (kWh/m²)Level
16.2Intense
26.2Intense
36.1Intense
46.1Intense
56.1Intense
66.1Intense
76.1Intense
86.1Intense
96.1Intense
106.0Intense
116.0Intense
126.0Intense
136.0Bright
146.0Bright
156.0Bright
165.9Bright
175.9Bright
185.9Bright
195.9Bright
205.9Bright
215.8Bright
225.8Bright
235.8Bright
245.8Bright
255.8Bright
265.8Bright
275.8Bright
285.7Bright
295.7Bright
305.7Bright
Planning a trip in September

Hazard calendar for Castries

In seasonPeak

In September, Castries sits inside its atlantic hurricane and rainy season season. The full year is below, with each hazard's peak months called out.

Castries sits in the Atlantic hurricane belt; the season peaks August–October.

Castries's rainy season runs June–November, when most of the year's rain falls.

Castries sees seasonal dust haze (June–July), heaviest in June.

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

Is September a good time to visit Castries?

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

3.9
Sightseeing
12th-best month of the year
5.3
Beach & pool
10th-best month of the year

September is a weaker month for outdoor sightseeing in Castries.

What to pack for Castries in September

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

In September, Castries sees daytime highs around 30°C and nights near 26°C. Pack light clothes and rain gear. Worth having: sun protection. About 19 days see rain.

light clothesrain gearsun protection

Sea temperature near Castries in September

The nearest coast averages about 29°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 19 km away) is warmest in September at about 29°C and coldest in February near 27°C.

The water stays above 20°C all year — warm enough for a swim any month.

26°28°30°JanFebMarAprMayJunJulAugSepOctNovDecwarmtropicalcomfortable to swim
Sea temperature (°C)Comfort
Jan27Warm
Feb27Warm
Mar27Warm
Apr27Warm
May28Warm
Jun28Warm
Jul28Tropical
Aug29Tropical
Sep29Tropical
Oct29Tropical
Nov29Tropical
Dec28Warm

UV index in Castries in September

LowModerateHighVery highExtreme

Clear-sky midday UV in September peaks around 12 (very high — sun protection essential). The full-year curve, shaded by WHO exposure level, is below.

Under clear skies, the midday UV index in Castries peaks around March 21 at about 14 (extreme) — sunscreen, a hat and midday shade are essential. It bottoms out near December 13 at about 8 (very high).

The index reaches 3 or more — the level where the WHO recommends sun protection — every month of the year.

025710JanFebMarAprMayJunJulAugSepOctNovDecExtremeVery highMar 21UV 14Dec 13UV 8
UV index (midday)Level
Jan9Very high
Feb12Extreme
Mar14Extreme
Apr13Extreme
May12Extreme
Jun11Extreme
Jul12Extreme
Aug11Extreme
Sep12Extreme
Oct11Extreme
Nov9Very high
Dec8Very high

Air quality in Castries in September

GoodModeratePoorUnhealthyVery unhealthy

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

Air quality in Castries is worst in June — around 29 µg/m³ PM2.5 (moderate), about 2.9× the cleanest month (December, 10 µg/m³).

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

010203040JanFebMarAprMayJunJulAugSepOctNovDecGoodModerateGoodJun 1929 µg/m³Dec 2310 µg/m³
PM2.5 (µg/m³)Level
Jan10Good
Feb14Moderate
Mar12Good
Apr16Moderate
May19Moderate
Jun29Moderate
Jul25Moderate
Aug21Moderate
Sep15Moderate
Oct18Moderate
Nov13Moderate
Dec10Good
Location & terrain

Where is Castries?

Castries sits at 14.0°N, 61.0°W, 119 m above sea level, in Saint Lucia. The nearest listed city is Gros Islet, 10 km away.

Gros IsletSoufriereVieux Fort

Topography around Castries

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

Within 3 km, the terrain around Castries has significant variations in elevation — a maximum elevation change of 266 m around an average of 45 m above sea level; within 16 km, large variations in elevation — a maximum elevation change of 900 m; within 80 km, large variations in elevation — a maximum elevation change of 1,191 m.

The land around Castries is covered by trees (46%) and water (35%) within 3 km, water (55%) and trees (42%) within 16 km, and water (89%) within 80 km.

3 km
266 m
16 km
900 m
80 km
1,191 m
treesgrasslandartificial surfaceswaterwetland
September weather nearby: Gros Islet 10 km · Soufriere 16 km · Vieux Fort 32 km · Ducos 65 km · Fort-de-France 68 km · Le Lamentin 69 km · Le François 70 km · Saint-Joseph 75 km

Saint Lucia travel facts

Travel advisory
Level 2
Exercise Increased Caution
Power plugs
Type A / B / G
240 V · 50 Hz
Prices
≈ 51% of US
price level, 2025
GDP per capita
$14,746
2025
Homicide rate
39
per 100k, 2023
Road deaths
29.8
per 100k/yr, 2019
Income group
Upper middle
World Bank
Religion
Roman Catholic 62%Protestant 26%none 6%other Christian 3%

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 Castries (13.9957°, -61.0061°, elevation 119 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. Tropical-cyclone seasons are the published climatological basin seasons (NOAA National Hurricane Center / regional warning centres). 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. 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).