San Isidro weather in September

In September, San Isidro sees average daytime highs of 24°C and overnight lows near 21°C, with 808 mm of rain across 30 wet days and about 12.1 hours of daylight. It is the 8th-warmest and 5th-wettest month of the year here.

Day-to-day highs hold fairly steady near 24°C through the month. The sky is clear or mostly clear about 0% of the time in September, and the air most often feels muggy.

Daylight stretches from about 12 h 12 min at the start of September to 11 h 54 min by month's end. Set against the rest of the year, September is San Isidro's 9th-clearest and 2nd-windiest month. For the whole year in context, see San Isidro's year-round climate.

Daytime high
24°
8th warmest
Overnight low
21°
7th coldest
Rainfall
808 mm
30 wet days
Daylight
12 h 06 min
5:28 AM – 5:31 PM
Cloud cover
95%
9th clearest
Wind
5 km/h
2nd windiest
Solar energy
4 kWh/m²
Travel score
3.4
out of 10

San Isidro is district in Pérez Zeledón canton, San José province, Costa Rica.

Density
182/km²
people per km²
Founded
1892

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 24°C through the month.

A typical September day in San Isidro reaches about 24°C in the afternoon and slips back to 21°C overnight — a 3°C spread between the day's warmth and the night's chill. On most days the high lands between 23°C and 25°C. Set against its neighbours, September runs on par with August and on par with October.

15°18°20°23°25°151015202530
Avg high (°C)Avg low (°C)
12421
22421
32421
42421
52421
62421
72421
82421
92421
102421
112421
122421
132421
142421
152421
162421
172421
182421
192421
202421
212421
222421
232421
242421
252421
262421
272421
282421
292421
302421

San Isidro weather by month

How September compares with the rest of the year at a glance. September is the 8th-warmest and 5th-wettest month here — the current month is highlighted below.

MonthHigh / Low (°C)Rainfall (mm)Wet daysDaylight (hours)Travel score
Jan24° / 20°21025.211.54.8
Feb24° / 20°14021.611.75.1
Mar25° / 21°13825.611.94.7
Apr25° / 21°33028.612.23.8
May24° / 21°73030.812.43.4
Jun24° / 21°70929.912.53.4
Jul24° / 21°8333112.53.4
Aug24° / 21°9333112.33.4
Sep24° / 21°8083012.13.4
Oct24° / 20°95230.811.83.4
Nov24° / 20°92429.911.63.5
Dec24° / 20°41328.811.54.1

Cloud cover in September

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 0% of the time in September.

Beyond those clear spells, partly cloudy skies cover about 0% of September, with mostly cloudy or overcast conditions the remaining 100%.

0%25%50%75%100%151015202530
Clearer (%)Cloudier (%)
10100
20100
30100
40100
50100
60100
70100
80100
90100
100100
110100
120100
130100
140100
150100
160100
170100
180100
190100
200100
210100
22199
23199
24199
25199
26199
27199
28199
29199
30199

Chance of precipitation in September

Any precipitation

San Isidro gets around 808 mm of rain over 30 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 100% and peaks near 100% on the wettest days.

0%20%40%60%80%100%151015202530
Rain chance (%)
1100
2100
3100
4100
5100
6100
7100
8100
9100
10100
11100
12100
13100
14100
15100
16100
17100
18100
19100
20100
21100
22100
23100
24100
25100
26100
27100
28100
2999
3099

Humidity in September

DryComfortableHumidMuggyOppressiveMiserable

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

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

0%25%50%75%100%151015202530
Muggy (%)Oppressive (%)
11000
21000
31000
41000
51000
61000
7991
8991
9991
10991
11991
12991
13991
14991
151000
161000
171000
181000
191000
201000
211000
221000
231000
241000
251000
261000
271000
281000
291000
301000

Wind in September

Winds average 5 km/h in September.

Across September, daily wind ranges from about 5 km/h on the calmest days to 6 km/h at its breeziest. It stays fairly steady from day to day.

0246810151015202530
Wind speed (km/h)Feels
15calm
25calm
35calm
45calm
55calm
65calm
75calm
85calm
95calm
105calm
115calm
125calm
135calm
145calm
155calm
165calm
175calm
186calm
196calm
206calm
216calm
226calm
236calm
246calm
256calm
266calm
276calm
286calm
296calm
306calm

Sunrise & sunset in September

DaylightNight

Daylight runs from about 12 h 12 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 18 minutes over September. Sunrise moves from 5:29 AM to 5:26 AM, and sunset from 5:40 PM to 5:22 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202530
Daylight (h)Sunrise (AM)Sunset (PM)
112.25:295:40
212.25:295:39
312.25:295:39
412.25:295:38
512.15:295:38
612.15:295:37
712.15:295:36
812.15:285:36
912.15:285:35
1012.15:285:34
1112.15:285:34
1212.15:285:33
1312.15:285:33
1412.15:285:32
1512.15:285:31
1612.15:285:31
1712.05:275:30
1812.05:275:29
1912.05:275:29
2012.05:275:28
2112.05:275:27
2212.05:275:27
2312.05:275:26
2412.05:275:26
2512.05:275:25
2612.05:275:24
2712.05:275:24
2811.95:265:23
2911.95:265:23
3011.95:265:22

Solar energy in September

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in September, about 4 kWh/m².

For context, solar energy here swings from a low near 3.71 kWh/m² to a high of 6.24 kWh/m² in March across the year — September's 4 kWh/m² sits near the bottom.

012345151015202530
Solar energy (kWh/m²)Level
14.1Bright
24.1Bright
34.1Bright
44.1Bright
54.1Bright
64.1Bright
74.1Bright
84.0Bright
94.0Bright
104.0Bright
114.0Bright
124.0Moderate
134.0Moderate
144.0Moderate
154.0Moderate
164.0Moderate
173.9Moderate
183.9Moderate
193.9Moderate
203.9Moderate
213.9Moderate
223.9Moderate
233.9Moderate
243.9Moderate
253.9Moderate
263.9Moderate
273.9Moderate
283.9Moderate
293.9Moderate
303.9Moderate
Planning a trip in September

Hazard calendar for San Isidro

In seasonPeak

In September, San Isidro sits inside its rainy season season. The full year is below, with each hazard's peak months called out.

San Isidro's rainy season runs May–November, when most of the year's rain falls.

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

Is September a good time to visit San Isidro?

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

3.4
Sightseeing
7th-best month of the year
3.0
Beach & pool
10th-best month of the year

September is a weaker month for outdoor sightseeing in San Isidro.

What to pack for San Isidro in September

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

In September, San Isidro sees daytime highs around 24°C and nights near 21°C. Pack rain gear. Worth having: light clothes. About 30 days see rain.

rain gearlight clothes

Sea temperature near San Isidro 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 28 km away) is warmest in March at about 30°C and coldest in November 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
Jan29Tropical
Feb30Tropical
Mar30Tropical
Apr30Tropical
May29Tropical
Jun29Tropical
Jul29Tropical
Aug29Tropical
Sep29Tropical
Oct28Tropical
Nov28Warm
Dec28Tropical

UV index in San Isidro in September

LowModerateHighVery highExtreme

Clear-sky midday UV in September peaks around 13 (very high — sun protection essential). The full-year curve, shaded by WHO exposure level, is below.

Under clear skies, the midday UV index in San Isidro peaks around March 16 at about 14 (extreme) — sunscreen, a hat and midday shade are essential. It bottoms out near December 16 at about 10 (extreme).

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

025710JanFebMarAprMayJunJulAugSepOctNovDecExtremeMar 16UV 14Dec 16UV 10
UV index (midday)Level
Jan12Extreme
Feb14Extreme
Mar15Extreme
Apr14Extreme
May13Extreme
Jun13Extreme
Jul12Extreme
Aug13Extreme
Sep13Extreme
Oct12Extreme
Nov12Extreme
Dec10Extreme
Location & terrain

Where is San Isidro?

San Isidro sits at 9.4°N, 83.7°W, 713 m above sea level, in Costa Rica. The nearest listed city is Manuel Antonio, 51 km away.

Manuel AntonioParaísoTurrialbaCartagoSan DiegoPatarráSan MiguelAserrí

Topography around San Isidro

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

Within 3 km, the terrain around San Isidro has only modest variations in elevation — a maximum elevation change of 211 m around an average of 723 m above sea level; within 16 km, very significant variations in elevation — a maximum elevation change of 2,363 m; within 80 km, extreme variations in elevation — a maximum elevation change of 3,764 m.

The land around San Isidro is covered by trees (40%), grassland (31%) and artificial surfaces (28%) within 3 km, trees (71%) and grassland (27%) within 16 km, and trees (67%) and water (22%) within 80 km.

3 km
211 m
16 km
2,363 m
80 km
3,764 m
treesgrasslandartificial surfaceswatermangroves
September weather nearby: Manuel Antonio 51 km · Paraíso 56 km · Turrialba 60 km · Cartago 60 km · San Diego 68 km · Patarrá 68 km · San Miguel 69 km · Aserrí 70 km

Costa Rica travel facts

Travel advisory
Level 2
Exercise Increased Caution
Power plugs
Type A / B
120 V · 60 Hz
Prices
≈ 59% of US
price level, 2025
GDP per capita
$19,970
2025
Happiness
7.4 / 10
World Happiness, 2025
Safe drinking water
81%
of population, 2024
Homicide rate
17.7
per 100k, 2023
Road deaths
14.8
per 100k/yr, 2019
Income group
High
World Bank
English
Moderate
EF EPI 516
Religion
Roman Catholic 48%none 27%Evangelical and Pentecostal 20%other 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 San Isidro (9.3674°, -83.6971°, elevation 713 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).