Climate and average weather in San Marcos
In San Marcos, the weather is sweltering, wet, and mostly clear and remarkably steady, with daytime highs holding near sweltering levels all year. The wettest stretch peaks around September.
Over the course of the year, the temperature in San Marcos typically varies from 20°C to 33°C, and is rarely below 17°C or above 35°C. March is the hottest month of the year, while October is the coldest.
Based on the travel score, the best times of year to visit San Marcos for warm-weather activities are from early January to early March and early November to late December.
- Hottest
- Mar
- 33°
- Coldest
- Oct
- 21°
- Wettest
- Sep
- 303 mm
- Driest
- Jan
- 2 mm
- Rain / yr
- 1535 mm
- 176 wet days
- Daylight
- 11.2–12.8 h
- shortest–longest
- Elevation
- 733 m
- 13.7°N
- Clearest
- Jan
- 25% cloud
San Marcos weather by month, at a glance
The whole year in one picture — sky, rain, humidity, temperature and travel score. Click any band to jump to its full chart.
Each stripe is one measure across the whole year, stacked so a single day reads top to bottom. The sky band runs overcast grey on top down to clear blue at the base — more blue means sunnier — followed by the rainfall curve, the humidity band, a temperature strip that tints each stretch of the year by how warm its average high is, and the travel-score line at the foot. Scan straight down any date to read that day across every measure at once; the score climbs highest around early January to early March.
Temperature through the year
Daily average highs and lows in San Marcos, from 1991–2020 of climate data. The shaded bands show the range most days fall in — 10th to 90th percentile.
Temperatures in San Marcos stay fairly even through the year, without a distinct hot or cool season. The warmest month is March, with an average high of 33°C and low of 21°C; the coolest is October, with an average low of 21°C and high of 29°C.
Days typically run about 10°C warmer than nights, with the widest day–night swing (around 13°C) in February.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Avg high (°C) | 32 | 33 | 33 | 33 | 31 | 30 | 31 | 31 | 30 | 29 | 31 | 31 |
| Avg low (°C) | 20 | 20 | 21 | 22 | 22 | 22 | 22 | 22 | 22 | 21 | 20 | 20 |
| Avg high (°C) | Avg low (°C) | |
|---|---|---|
| Jan | 32 | 20 |
| Feb | 33 | 20 |
| Mar | 33 | 21 |
| Apr | 33 | 22 |
| May | 31 | 22 |
| Jun | 30 | 22 |
| Jul | 31 | 22 |
| Aug | 31 | 22 |
| Sep | 30 | 22 |
| Oct | 29 | 21 |
| Nov | 31 | 20 |
| Dec | 31 | 20 |
How hot and cold San Marcos really feels
The felt-temperature range through the year — heat index on the day's high (summer humidity), wind chill on the night's low (winter wind). The dashed lines are the plain thermometer; the gap is how much hotter or colder it really feels.
On the hottest afternoons, once humidity is folded in, San Marcos feels like about 34°C (around May 7). About 244 days a year carry some heat stress, peaking in May.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Feels-like high (°C) | 32 | 33 | 33 | 34 | 34 | 33 | 33 | 33 | 32 | 32 | 31 | 31 |
| Air high (°C) | 32 | 33 | 33 | 33 | 31 | 30 | 31 | 31 | 30 | 29 | 31 | 31 |
| Feels-like low (°C) | 19 | 20 | 21 | 22 | 22 | 22 | 22 | 22 | 22 | 21 | 20 | 20 |
| Air low (°C) | 20 | 20 | 21 | 22 | 22 | 22 | 22 | 22 | 22 | 21 | 20 | 20 |
| Feels-like high (°C) | Air high (°C) | Feels-like low (°C) | Air low (°C) | |
|---|---|---|---|---|
| Jan | 32 | 32 | 19 | 20 |
| Feb | 33 | 33 | 20 | 20 |
| Mar | 33 | 33 | 21 | 21 |
| Apr | 34 | 33 | 22 | 22 |
| May | 34 | 31 | 22 | 22 |
| Jun | 33 | 30 | 22 | 22 |
| Jul | 33 | 31 | 22 | 22 |
| Aug | 33 | 31 | 22 | 22 |
| Sep | 32 | 30 | 22 | 22 |
| Oct | 32 | 29 | 21 | 21 |
| Nov | 31 | 31 | 20 | 20 |
| Dec | 31 | 31 | 20 | 20 |
Average hourly temperature in San Marcos
A compact picture of the whole year, hour by hour: each column is a day, each row an hour, and the color is the modeled average temperature. Darker overlays mark night, lighter ones the civil-twilight hours around sunrise and sunset.
Read left to right for the day of the year and top to bottom for the hour of the day; the color is the modeled temperature, cool blues through to hot reds on the same scale as the other charts. A vertical slice is a single day's swing — coolest just before dawn, warmest in the mid-afternoon — while a horizontal slice follows one hour across the seasons. The darker overlay marks night and the lighter one the twilight around sunrise and sunset. Colors run warmest on March afternoons, near 33°C, and coldest before dawn in October, near 21°C.
San Marcos weather by month
Every month at a glance. Click a month for its detailed page.
| Month | High / Low (°C) | Rainfall (mm) | Wet days | Daylight (hours) | Travel score |
|---|---|---|---|---|---|
| Jan | 32° / 20° | 2 | 0.6 | 11.3 | 5.5 |
| Feb | 33° / 20° | 2 | 0.5 | 11.5 | 4.9 |
| Mar | 33° / 21° | 10 | 2.9 | 11.9 | 4.3 |
| Apr | 33° / 22° | 50 | 11.3 | 12.3 | 3.7 |
| May | 31° / 22° | 222 | 24.9 | 12.6 | 2.9 |
| Jun | 30° / 22° | 248 | 26.3 | 12.8 | 2.9 |
| Jul | 31° / 22° | 186 | 22.3 | 12.7 | 3.1 |
| Aug | 31° / 22° | 230 | 26 | 12.5 | 2.9 |
| Sep | 30° / 22° | 303 | 28.4 | 12.1 | 2.8 |
| Oct | 29° / 21° | 232 | 23.3 | 11.7 | 3.6 |
| Nov | 31° / 20° | 45 | 7.6 | 11.4 | 5.1 |
| Dec | 31° / 20° | 7 | 1.4 | 11.2 | 5.6 |
Chance of rain
How likely it is to rain on a typical day, and how that shifts across the wetter and drier seasons.
San Marcos gets about 1535 mm of precipitation a year. On a typical day the chance of rain is very wet, but that rises and falls sharply with the seasons.
The wetter season lasts 6.3 months, from around Apr 24 to Oct 31, peaking in September at about 95% chance on a given day. The drier stretch runs the rest of the year, bottoming out around Feb 2.
September is the wettest month by volume, with 303 mm over about 28 wet days; January is the driest, with 2 mm.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Rain on a day (%) | 2 | 2 | 10 | 38 | 79 | 87 | 73 | 83 | 94 | 75 | 26 | 5 |
| Rain days | 1 | 1 | 3 | 11 | 25 | 26 | 22 | 26 | 28 | 23 | 8 | 1 |
| Rain on a day (%) | Rain days | |
|---|---|---|
| Jan | 2 | 1 |
| Feb | 2 | 1 |
| Mar | 10 | 3 |
| Apr | 38 | 11 |
| May | 79 | 25 |
| Jun | 87 | 26 |
| Jul | 73 | 22 |
| Aug | 83 | 26 |
| Sep | 94 | 28 |
| Oct | 75 | 23 |
| Nov | 26 | 8 |
| Dec | 5 | 1 |
Monthly rainfall
Over a full year, San Marcos collects about 1535 mm of rain across 176 wet days — roughly 128 mm in an average month.
It doesn’t fall evenly. September is the wettest month with 303 mm, while January is the driest at just 2 mm. The three wettest months alone bring about 51% of the year’s total.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Rainfall (mm) | 2 | 2 | 10 | 50 | 222 | 248 | 186 | 230 | 303 | 232 | 45 | 7 |
| Rain days | 1 | 1 | 3 | 11 | 25 | 26 | 22 | 26 | 28 | 23 | 8 | 1 |
| Rainfall (mm) | Rain days | |
|---|---|---|
| Jan | 2 | 1 |
| Feb | 2 | 1 |
| Mar | 10 | 3 |
| Apr | 50 | 11 |
| May | 222 | 25 |
| Jun | 248 | 26 |
| Jul | 186 | 22 |
| Aug | 230 | 26 |
| Sep | 303 | 28 |
| Oct | 232 | 23 |
| Nov | 45 | 8 |
| Dec | 7 | 1 |
Clouds and sunshine
How often the daytime sky is clear, partly cloudy or overcast.
In San Marcos, the average share of the sky covered by clouds shows significant seasonal variation over the course of the year.
The clearer part of the year begins around November 3 and lasts for 5.9 months, ending around April 30. The clearest month is February, when the sky is clear, mostly clear, or partly cloudy 93% of the time on average.
The cloudier part of the year begins around May 1 and lasts for 6.1 months, ending around November 2. The cloudiest month is September, when it is overcast or mostly cloudy 85% of the time.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Clearer (%) | 92 | 93 | 88 | 72 | 30 | 17 | 28 | 25 | 15 | 29 | 67 | 88 |
| Cloudier (%) | 8 | 7 | 12 | 28 | 70 | 83 | 72 | 75 | 85 | 71 | 33 | 12 |
| Clearer (%) | Cloudier (%) | |
|---|---|---|
| Jan | 92 | 8 |
| Feb | 93 | 7 |
| Mar | 88 | 12 |
| Apr | 72 | 28 |
| May | 30 | 70 |
| Jun | 17 | 83 |
| Jul | 28 | 72 |
| Aug | 25 | 75 |
| Sep | 15 | 85 |
| Oct | 29 | 71 |
| Nov | 67 | 33 |
| Dec | 88 | 12 |
Daylight, sunrise and sunset
Hours of daylight through the year, with sunrise and sunset times.
The gold band is daylight — sunrise runs along its lower edge, sunset along the upper — so it widens toward summer and pinches toward winter, with night the dark area above and below. The longest day, around June 2, brings about 12 h 48 min of light; the shortest, around January 1, only 11 h 12 min — a swing of roughly 1 h 36 min.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Daylight (h) | 11.3 | 11.5 | 11.9 | 12.3 | 12.6 | 12.8 | 12.7 | 12.5 | 12.1 | 11.7 | 11.4 | 11.2 |
| Sunrise (AM) | 6:28 | 6:25 | 6:09 | 5:48 | 5:34 | 5:33 | 5:40 | 5:47 | 5:49 | 5:51 | 6:01 | 6:17 |
| Sunset (PM) | 5:44 | 5:58 | 6:04 | 6:06 | 6:12 | 6:21 | 6:24 | 6:15 | 5:53 | 5:32 | 5:23 | 5:29 |
| Daylight (h) | Sunrise (AM) | Sunset (PM) | |
|---|---|---|---|
| Jan | 11.3 | 6:28 | 5:44 |
| Feb | 11.5 | 6:25 | 5:58 |
| Mar | 11.9 | 6:09 | 6:04 |
| Apr | 12.3 | 5:48 | 6:06 |
| May | 12.6 | 5:34 | 6:12 |
| Jun | 12.8 | 5:33 | 6:21 |
| Jul | 12.7 | 5:40 | 6:24 |
| Aug | 12.5 | 5:47 | 6:15 |
| Sep | 12.1 | 5:49 | 5:53 |
| Oct | 11.7 | 5:51 | 5:32 |
| Nov | 11.4 | 6:01 | 5:23 |
| Dec | 11.2 | 6:17 | 5:29 |
Sunny days
How many genuinely sunny days each month brings — days the sky stays clear or mostly clear — banded into plain-language zones.
San Marcos averages about 12 sunny days a month — counting the days the sky stays clear or mostly clear — with a clear seasonal swing between 1 and 25 days.
The sunnier stretch runs 5.5 months, from around Nov 6 to Apr 20. The sunniest month is February, with roughly 25 sunny days (brilliant).
The greyest month is June, down near 2 sunny days — about 93% fewer than the February peak.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Sunny days | 25 | 23 | 21 | 13 | 4 | 2 | 3 | 3 | 1 | 4 | 15 | 23 |
| Sky | Brilliant | Brilliant | Bright | Mixed | Gloomy | Gloomy | Gloomy | Gloomy | Gloomy | Gloomy | Bright | Bright |
| Sunny days | Sky | |
|---|---|---|
| Jan | 25 | Brilliant |
| Feb | 23 | Brilliant |
| Mar | 21 | Bright |
| Apr | 13 | Mixed |
| May | 4 | Gloomy |
| Jun | 2 | Gloomy |
| Jul | 3 | Gloomy |
| Aug | 3 | Gloomy |
| Sep | 1 | Gloomy |
| Oct | 4 | Gloomy |
| Nov | 15 | Bright |
| Dec | 23 | Bright |
Humidity comfort
Share of days at each humidity comfort level, based on the dew point — the measure that tracks how muggy it actually feels.
Humidity comfort is graded by the dew point — the temperature at which the air would be fully saturated — because it tracks how muggy it actually feels far better than relative humidity does. A low dew point feels dry and crisp; a high one feels sticky and oppressive no matter the reading on a humidity gauge.
In San Marcos, how humid it feels changes dramatically over the year.
The more humid part of the year lasts 7.6 months, from around April 2 to November 17. The muggiest month is June, when the air feels humid, muggy or worse about 100% of the time.
The most comfortable stretch runs from around November 18 to April 1, and February is the most comfortable month — the air is dry or comfortable 43% of the time.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Dry (%) | 8 | 6 | 6 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 2 | 4 |
| Comfortable (%) | 37 | 37 | 23 | 7 | 1 | 0 | 0 | 0 | 0 | 1 | 11 | 24 |
| Humid (%) | 49 | 46 | 40 | 24 | 6 | 0 | 2 | 1 | 0 | 7 | 32 | 54 |
| Muggy (%) | 6 | 11 | 29 | 54 | 44 | 33 | 66 | 59 | 36 | 44 | 47 | 18 |
| Oppressive (%) | 0 | 0 | 1 | 13 | 49 | 67 | 32 | 40 | 64 | 48 | 8 | 1 |
| Dry (%) | Comfortable (%) | Humid (%) | Muggy (%) | Oppressive (%) | |
|---|---|---|---|---|---|
| Jan | 8 | 37 | 49 | 6 | 0 |
| Feb | 6 | 37 | 46 | 11 | 0 |
| Mar | 6 | 23 | 40 | 29 | 1 |
| Apr | 1 | 7 | 24 | 54 | 13 |
| May | 0 | 1 | 6 | 44 | 49 |
| Jun | 0 | 0 | 0 | 33 | 67 |
| Jul | 0 | 0 | 2 | 66 | 32 |
| Aug | 0 | 0 | 1 | 59 | 40 |
| Sep | 0 | 0 | 0 | 36 | 64 |
| Oct | 0 | 1 | 7 | 44 | 48 |
| Nov | 2 | 11 | 32 | 47 | 8 |
| Dec | 4 | 24 | 54 | 18 | 1 |
Wind
Average wind speed through the year, banded into plain-language speed zones so a number reads as 'breezy' or 'calm' without knowing the scale.
This is the average sustained wind speed at the standard 10 metres above open ground — the steady flow a weather station reports, not the sharper gusts that come and go, which can run half again as fast. It's the number that says whether a place is generally breezy or calm.
Across the year, average wind speed in San Marcos is typically calm, near 6 km/h, and varies little with the seasons.
The windier part of the year lasts 5.3 months, from around Nov 1 to Apr 9. The windiest month is January, averaging about 8 km/h (calm).
The calmer part of the year runs from around Apr 10 to Oct 31, with June the calmest month at about 4 km/h.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Wind speed (km/h) | 8 | 7 | 7 | 5 | 4 | 4 | 5 | 4 | 4 | 5 | 7 | 8 |
| Feels | calm | calm | calm | calm | calm | calm | calm | calm | calm | calm | calm | calm |
| Wind speed (km/h) | Feels | |
|---|---|---|
| Jan | 8 | calm |
| Feb | 7 | calm |
| Mar | 7 | calm |
| Apr | 5 | calm |
| May | 4 | calm |
| Jun | 4 | calm |
| Jul | 5 | calm |
| Aug | 4 | calm |
| Sep | 4 | calm |
| Oct | 5 | calm |
| Nov | 7 | calm |
| Dec | 8 | calm |
Hazard calendar for San Marcos
When the seasonal hazards worth planning around — the rainy season, tropical-cyclone risk and dust haze — are active through the year.
San Marcos sits in the Atlantic hurricane belt; the season peaks August–October.
San Marcos's monsoon runs May–October, when most of the year's rain falls.
Best time to visit San Marcos
To characterize how pleasant the weather is in San Marcos throughout the year, we compute two travel scores — one for general sightseeing, one for beach and pool weather.
Around late February, San Marcos is still near the tail of its best-weather window — great conditions with the peak-season crowds already thinning.
Inferred from the travel-score curve; month-by-month visitor numbers are a planned addition.
The travel score favors clear, rainless days with daytime highs between 18°C and 28°C. Based on this score, the best time of year to visit San Marcos for general outdoor tourist activities is from early November to early March, with a peak score in the second week of December.
The travel score (filled area), and its constituents: the temperature score (red line), the cloud cover score (blue line), and the precipitation score (green line).
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Travel score (0–10) | 5.5 | 4.9 | 4.3 | 3.7 | 2.9 | 2.9 | 3.1 | 2.9 | 2.8 | 3.6 | 5.1 | 5.6 |
| Rating | fair | fair | fair | fair | poor | poor | poor | poor | poor | fair | fair | good |
| Travel score (0–10) | Rating | |
|---|---|---|
| Jan | 5.5 | fair |
| Feb | 4.9 | fair |
| Mar | 4.3 | fair |
| Apr | 3.7 | fair |
| May | 2.9 | poor |
| Jun | 2.9 | poor |
| Jul | 3.1 | poor |
| Aug | 2.9 | poor |
| Sep | 2.8 | poor |
| Oct | 3.6 | fair |
| Nov | 5.1 | fair |
| Dec | 5.6 | good |
The beach/pool score favors clear, rainless days with daytime highs between 24°C and 34°C. Based on this score, the best time of year to visit San Marcos for hot-weather activities is from mid November to early April, with a peak score in the third week of January.
The beach/pool score (filled area), and its constituents: the temperature score (red line), the cloud cover score (blue line), and the precipitation score (green line).
What to pack for San Marcos, by month
Month by month, what's worth putting in the bag — from the temperature range, rain chance, sun and wind. Tap a month for a quick packing note.
San Marcos packs about the same all year — highs hold near 33°C. Across the year the things worth having are light clothes, sun protection and rain gear.
In March, San Marcos sees daytime highs around 33°C and nights near 21°C. Pack light clothes and sun protection.
Sea temperature near San Marcos
Average ocean temperature at the nearest coast, month by month, banded into swim-comfort zones — the other half of the beach question.
The sea at the nearest coast (about 32 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.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Sea temperature (°C) | 28 | 28 | 29 | 29 | 30 | 30 | 30 | 30 | 30 | 29 | 29 | 29 |
| Comfort | Tropical | Tropical | Tropical | Tropical | Tropical | Tropical | Tropical | Tropical | Tropical | Tropical | Tropical | Tropical |
| Sea temperature (°C) | Comfort | |
|---|---|---|
| Jan | 28 | Tropical |
| Feb | 28 | Tropical |
| Mar | 29 | Tropical |
| Apr | 29 | Tropical |
| May | 30 | Tropical |
| Jun | 30 | Tropical |
| Jul | 30 | Tropical |
| Aug | 30 | Tropical |
| Sep | 30 | Tropical |
| Oct | 29 | Tropical |
| Nov | 29 | Tropical |
| Dec | 29 | Tropical |
UV index (midday) in San Marcos by month
Clear-sky midday UV index through the year, shaded by the WHO exposure levels — how much sun protection each month calls for.
Under clear skies, the midday UV index in San Marcos peaks around March 21 at about 13 (extreme) — sunscreen, a hat and midday shade are essential. It bottoms out near December 12 at about 9 (very high).
The index reaches 3 or more — the level where the WHO recommends sun protection — every month of the year.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| UV index (midday) | 9 | 13 | 13 | 13 | 12 | 13 | 12 | 12 | 11 | 11 | 9 | 9 |
| Level | Very high | Extreme | Extreme | Extreme | Extreme | Extreme | Extreme | Extreme | Extreme | Extreme | Very high | Very high |
| UV index (midday) | Level | |
|---|---|---|
| Jan | 9 | Very high |
| Feb | 13 | Extreme |
| Mar | 13 | Extreme |
| Apr | 13 | Extreme |
| May | 12 | Extreme |
| Jun | 13 | Extreme |
| Jul | 12 | Extreme |
| Aug | 12 | Extreme |
| Sep | 11 | Extreme |
| Oct | 11 | Extreme |
| Nov | 9 | Very high |
| Dec | 9 | Very high |
Average hourly UV index in San Marcos
Modeled clear-sky UV for every hour of every day — when in the day sun protection actually matters.
The whole year hour by hour: each column is a day, each row an hour, and the color is the modeled clear-sky UV index — the midday peak scaled down as the sun sits lower in the sky. Darker overlays mark night, lighter ones the civil-twilight hours around sunrise and sunset.
UV falls off far faster than brightness as the sun drops, so even in March the burn window is concentrated in the middle of the day: about 8 hours a day reach index 3 (protection recommended), and 6 hours reach 6 or more. Mornings and late afternoons stay comparatively gentle year round.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| UV ≥ 3 (h/day) | 7 | 7.5 | 8 | 8 | 8 | 8.5 | 8.5 | 8 | 7.5 | 7.5 | 7 | 6.5 |
| UV ≥ 6 (h/day) | 4.5 | 6 | 6 | 6.5 | 6 | 6.5 | 6 | 6 | 5.5 | 5.5 | 4.5 | 4 |
| UV ≥ 3 (h/day) | UV ≥ 6 (h/day) | |
|---|---|---|
| Jan | 7 | 4.5 |
| Feb | 7.5 | 6 |
| Mar | 8 | 6 |
| Apr | 8 | 6.5 |
| May | 8 | 6 |
| Jun | 8.5 | 6.5 |
| Jul | 8.5 | 6 |
| Aug | 8 | 6 |
| Sep | 7.5 | 5.5 |
| Oct | 7.5 | 5.5 |
| Nov | 7 | 4.5 |
| Dec | 6.5 | 4 |
Air quality in San Marcos by month
Average fine-particle pollution (PM2.5) through the year — so you can see which months the air is worst, not just the yearly average.
Air quality in San Marcos is worst in April — around 43 µg/m³ PM2.5 (poor), about 1.6× the cleanest month (September, 26 µg/m³).
Modeled monthly averages (CAMS reanalysis, 2015–2024).
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| PM2.5 (µg/m³) | 34 | 35 | 35 | 43 | 40 | 27 | 30 | 27 | 26 | 29 | 35 | 36 |
| Level | Moderate | Moderate | Poor | Poor | Poor | Moderate | Moderate | Moderate | Moderate | Moderate | Moderate | Poor |
| PM2.5 (µg/m³) | Level | |
|---|---|---|
| Jan | 34 | Moderate |
| Feb | 35 | Moderate |
| Mar | 35 | Poor |
| Apr | 43 | Poor |
| May | 40 | Poor |
| Jun | 27 | Moderate |
| Jul | 30 | Moderate |
| Aug | 27 | Moderate |
| Sep | 26 | Moderate |
| Oct | 29 | Moderate |
| Nov | 35 | Moderate |
| Dec | 36 | Poor |
Growing season
San Marcos is frost-free year round — even the coldest nights rarely reach freezing, so there is no start or end to the growing season.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Frost-free chance (%) | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 100 |
| Frost nights | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| Frost-free chance (%) | Frost nights | |
|---|---|---|
| Jan | 100 | 0 |
| Feb | 100 | 0 |
| Mar | 100 | 0 |
| Apr | 100 | 0 |
| May | 100 | 0 |
| Jun | 100 | 0 |
| Jul | 100 | 0 |
| Aug | 100 | 0 |
| Sep | 100 | 0 |
| Oct | 100 | 0 |
| Nov | 100 | 0 |
| Dec | 100 | 0 |
Growing degree days
Growing degree days tally heat above 10°C: each day adds however many degrees its average temperature runs over that threshold, and cold days add nothing. San Marcos banks about 5,875 degree days a year, and the running total — which growers use to time plantings and predict maturity — climbs fastest around April.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Growing degree days (°C·days) | 483 | 456 | 523 | 518 | 518 | 480 | 509 | 506 | 468 | 474 | 462 | 479 |
| Growing degree days (°C·days) | |
|---|---|
| Jan | 483 |
| Feb | 456 |
| Mar | 523 |
| Apr | 518 |
| May | 518 |
| Jun | 480 |
| Jul | 509 |
| Aug | 506 |
| Sep | 468 |
| Oct | 474 |
| Nov | 462 |
| Dec | 479 |
Solar energy
Average daily shortwave solar energy reaching the ground, banded into brightness zones so the number means something at a glance.
Solar energy is how much sunlight actually reaches the ground each day, measured in kilowatt-hours per square metre (kWh/m²) — the combined effect of how long the sun is up, how high it climbs, and how much cloud gets in the way. It's the raw fuel a solar panel has to work with: for scale, 1 kWh/m² a day is dim and wintry, while 7+ is desert-bright.
San Marcos receives about 5.5 kWh/m² a day of solar energy on average — bright — with a clear seasonal swing between 4.6 and 6.2 kWh/m².
The brighter stretch of the year lasts 3.7 months, from around Jan 23 to May 16. The brightest month is March, averaging about 6.2 kWh/m² (intense).
The dimmest month is October, down near 4.7 kWh/m² — roughly 24% less than the March peak.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Solar energy (kWh/m²) | 5.4 | 5.8 | 6.2 | 6.1 | 5.5 | 5.2 | 5.9 | 5.6 | 4.9 | 4.7 | 5.2 | 5.2 |
| Level | Bright | Bright | Intense | Intense | Bright | Bright | Bright | Bright | Bright | Bright | Bright | Bright |
| Solar energy (kWh/m²) | Level | |
|---|---|---|
| Jan | 5.4 | Bright |
| Feb | 5.8 | Bright |
| Mar | 6.2 | Intense |
| Apr | 6.1 | Intense |
| May | 5.5 | Bright |
| Jun | 5.2 | Bright |
| Jul | 5.9 | Bright |
| Aug | 5.6 | Bright |
| Sep | 4.9 | Bright |
| Oct | 4.7 | Bright |
| Nov | 5.2 | Bright |
| Dec | 5.2 | Bright |
Where is San Marcos?
San Marcos sits at 13.7°N, 89.2°W, 733 m above sea level, in El Salvador. The nearest listed city is San Salvador, 3.0 km away.
Topography around San Marcos
How much the land rises and falls, and what covers it, within 3, 16 and 80 km of San Marcos.
Within 3 km, the terrain around San Marcos has significant variations in elevation — a maximum elevation change of 567 m around an average of 854 m above sea level; within 16 km, very significant variations in elevation — a maximum elevation change of 1,865 m; within 80 km, extreme variations in elevation — a maximum elevation change of 2,703 m.
The land around San Marcos is covered by trees (69%) and artificial surfaces (27%) within 3 km, trees (72%) within 16 km, and trees (46%), water (25%) and grassland (21%) within 80 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
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 Marcos (13.6611°, -89.1825°, elevation 733 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).