La Unión weather in September

In September, La Unión sees average daytime highs of 29°C and overnight lows near 26°C, with 375 mm of rain across 25.1 wet days and about 12.1 hours of daylight. It is the 11th-warmest and 1st-wettest month of the year here.

Day-to-day highs hold fairly steady near 29°C through the month. The sky is clear or mostly clear about 14% 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 La Unión's 11th-clearest and 11th-windiest month. For the whole year in context, see La Unión's year-round climate.

Daytime high
29°
11th warmest
Overnight low
26°
3rd coldest
Rainfall
375 mm
25.1 wet days
Daylight
12 h 06 min
5:43 AM – 5:48 PM
Cloud cover
72%
11th clearest
Wind
9 km/h
11th windiest
Solar energy
5.67 kWh/m²
Travel score
3.6
out of 10

La Unión is city in El Salvador.

Density
186/km²
people per km²
Founded
1854

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 29°C through the month.

A typical September day in La Unión reaches about 29°C in the afternoon and slips back to 26°C overnight — a 3°C spread between the day's warmth and the night's chill. On most days the high lands between 27°C and 30°C. Set against its neighbours, September runs about 1°C cooler than August and on par with October.

20°25°30°35°151015202530
Avg high (°C)Avg low (°C)
12926
22926
32926
42926
52926
62926
72926
82926
92926
102926
112926
122926
132926
142926
152926
162926
172926
182926
192926
202926
212926
222926
232926
242926
252826
262826
272826
282826
292826
302826

How September really feels in La Unión

Once humidity and wind are folded in, September averages 24 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
24
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.

La Unión weather by month

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

MonthHigh / Low (°C)Rainfall (mm)Wet daysDaylight (hours)Travel score
Jan29° / 26°10.411.37.4
Feb29° / 26°20.611.67.4
Mar29° / 27°82.611.97.0
Apr29° / 27°409.912.35.6
May29° / 27°27721.412.64.0
Jun30° / 27°31320.912.83.8
Jul30° / 27°14612.412.74.5
Aug30° / 27°25619.212.44.1
Sep29° / 26°37525.112.13.6
Oct28° / 26°34422.111.74.2
Nov29° / 26°486.711.46.2
Dec29° / 26°30.911.27.2

Cloud cover in September

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 14% of the time in September.

Beyond those clear spells, partly cloudy skies cover about 17% of September, with mostly cloudy or overcast conditions the remaining 69%.

0%25%50%75%100%151015202530
Clearer (%)Cloudier (%)
13664
23565
33565
43664
53565
63664
73565
83466
93466
103466
113466
123268
133268
143268
153169
163070
173070
182971
192971
202872
212872
222773
232773
242674
252674
262674
272872
282872
292872
302872

Chance of precipitation in September

Any precipitation

La Unión gets around 375 mm of rain over 25.1 wet days in September, the wettest month. The line is the day-by-day chance of measurable precipitation.

Day to day, the chance of measurable rain averages around 83% and peaks near 89% on the wettest days. The odds climb toward the end of the month.

0%20%40%60%80%100%151015202530
Rain chance (%)
175
276
376
477
577
677
778
878
979
1079
1180
1281
1381
1482
1583
1684
1785
1886
1987
2088
2188
2289
2389
2489
2589
2688
2788
2887
2986
3085

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 83% of days. Sticky, muggy-or-worse air turns up on roughly 100% of them.

0%25%50%75%100%151015202530
Muggy (%)Oppressive (%)Miserable (%)
108020
208020
308020
408020
508020
608020
708020
808020
908020
1008020
1108119
1208119
1308119
1408119
1508119
1608218
1708218
1808218
1908317
2008416
2108416
2208515
2308614
2408614
2508713
2608812
2708812
2818811
2918811
3018811

Wind in September

Winds average 9 km/h in September.

Across September, daily wind ranges from about 9 km/h on the calmest days to 9 km/h at its breeziest. It stays fairly steady from day to day.

051015151015202530
Wind speed (km/h)Feels
19calm
29calm
39calm
49calm
59calm
69calm
79calm
89calm
99calm
109calm
119calm
129calm
139calm
149calm
159calm
169calm
179calm
189calm
199calm
209calm
219calm
229calm
239calm
249calm
259calm
269calm
279calm
289calm
299calm
309calm

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 5:43 AM to 5:44 AM, and sunset from 5:59 PM to 5:38 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202530
Daylight (h)Sunrise (AM)Sunset (PM)
112.35:435:59
212.25:435:58
312.25:435:58
412.25:435:57
512.25:435:56
612.25:435:55
712.25:435:55
812.25:435:54
912.25:435:53
1012.15:435:52
1112.15:435:52
1212.15:435:51
1312.15:435:50
1412.15:435:49
1512.15:435:49
1612.15:435:48
1712.15:445:47
1812.05:445:46
1912.05:445:46
2012.05:445:45
2112.05:445:44
2212.05:445:43
2312.05:445:43
2412.05:445:42
2512.05:445:41
2611.95:445:40
2711.95:445:40
2811.95:445:39
2911.95:445:38
3011.95:445:38

Solar energy in September

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in September, about 5.67 kWh/m².

For context, solar energy here swings from a low near 5.18 kWh/m² to a high of 6.78 kWh/m² in March across the year — September's 5.67 kWh/m² falls in the middle.

0246151015202530
Solar energy (kWh/m²)Level
16.0Intense
26.0Intense
36.0Intense
46.0Intense
56.0Bright
66.0Bright
76.0Bright
85.9Bright
95.9Bright
105.9Bright
115.8Bright
125.8Bright
135.8Bright
145.8Bright
155.7Bright
165.7Bright
175.6Bright
185.6Bright
195.6Bright
205.5Bright
215.5Bright
225.4Bright
235.4Bright
245.4Bright
255.3Bright
265.3Bright
275.3Bright
285.3Bright
295.3Bright
305.2Bright
Planning a trip in September

Hazard calendar for La Unión

In seasonPeak

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

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

La Unión's monsoon runs August–October, when most of the year's rain falls.

Atlantic hurricane
Monsoon
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec

Is September a good time to visit La Unión?

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

3.6
Sightseeing
12th-best month of the year
4.5
Beach & pool
12th-best month of the year

September is a weaker month for outdoor sightseeing in La Unión.

What to pack for La Unión in September

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

In September, La Unión sees daytime highs around 29°C and nights near 26°C. Pack light clothes and rain gear. Worth having: sun protection. About 25 days see rain.

light clothesrain gearsun protection

Sea temperature near La Unión in September

The nearest coast averages about 30°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 24 km away) is warmest in August at about 30°C and coldest in January near 28°C.

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

26°28°30°32°JanFebMarAprMayJunJulAugSepOctNovDecwarmtropicalcomfortable to swim
Sea temperature (°C)Comfort
Jan28Warm
Feb28Warm
Mar28Tropical
Apr29Tropical
May30Tropical
Jun30Tropical
Jul30Tropical
Aug30Tropical
Sep30Tropical
Oct29Tropical
Nov29Tropical
Dec28Tropical

UV index in La Unión 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 La Unión peaks around March 20 at about 13 (extreme) — sunscreen, a hat and midday shade are essential. It bottoms out near December 14 at about 9 (very high).

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

025710JanFebMarAprMayJunJulAugSepOctNovDecExtremeVery highMar 20UV 13Dec 14UV 9
UV index (midday)Level
Jan10Extreme
Feb12Extreme
Mar13Extreme
Apr13Extreme
May12Extreme
Jun13Extreme
Jul11Extreme
Aug11Extreme
Sep12Extreme
Oct11Extreme
Nov9Very high
Dec9Very high

Air quality in La Unión 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 La Unión is worst in April — around 34 µg/m³ PM2.5 (moderate), about 3.3× the cleanest month (January, 10 µg/m³).

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

010203040JanFebMarAprMayJunJulAugSepOctNovDecGoodModerateGoodApr 2233 µg/m³Jan 1010 µg/m³
PM2.5 (µg/m³)Level
Jan10Good
Feb12Good
Mar20Moderate
Apr34Moderate
May32Moderate
Jun21Moderate
Jul24Moderate
Aug20Moderate
Sep18Moderate
Oct17Moderate
Nov14Moderate
Dec10Good
Location & terrain

Where is La Unión?

La Unión sits at 13.3°N, 87.8°W, 10 m above sea level, in El Salvador. The nearest listed city is Langue, 37 km away.

LangueSan MiguelSan Francisco GoteraSan Rafael OrienteUsulutánSantiago de María

Topography around La Unión

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

Within 3 km, the terrain around La Unión has only modest variations in elevation — a maximum elevation change of 245 m around an average of 38 m above sea level; within 16 km, very significant variations in elevation — a maximum elevation change of 1,230 m; within 80 km, very significant variations in elevation — a maximum elevation change of 2,074 m.

The land around La Unión is covered by water (43%) and trees (33%) within 3 km, trees (39%) and water (32%) within 16 km, and trees (42%) and water (32%) within 80 km.

3 km
245 m
16 km
1,230 m
80 km
2,074 m
treesshrubsgrasslandcroplandartificial surfacesbare terrainwatermangroves
September weather nearby: Langue 37 km · San Miguel 40 km · San Lorenzo 44 km · San Francisco Gotera 49 km · San Rafael Oriente 55 km · Marcovia 58 km · Usulután 65 km · Santiago de María 69 km

El Salvador travel facts

Travel advisory
Level 1
Exercise Normal Precautions
Power plugs
Type A / B
115 V · 60 Hz
Prices
≈ 41% of US
price level, 2025
GDP per capita
$5,767
2025
Happiness
6.6 / 10
World Happiness, 2025
Homicide rate
7.9
per 100k, 2022
Road deaths
20.9
per 100k/yr, 2019
Income group
Upper middle
World Bank
English
Moderate
EF EPI 523
Religion
Roman Catholic 44%Protestant 40%none 16%

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 La Unión (13.3392°, -87.8433°, elevation 10 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).