San Juan weather in September
September in San Juan: sweltering, rainy, with clean air — a good time to visit.
#12 of 12 months in San Juan · #515 of 604 destinations to visit in September · comfort 60/100 (tier C)
Updated June 2026 · climate normals from ERA5 reanalysis
San Juan climate normals — September
| Daytime high | 32°C / 89°F | 🔥 sweltering |
|---|---|---|
| Nighttime low | 25°C / 77°F | |
| Feels like (high) | 37°C / 99°F | |
| Rainfall | 145 mm / 5.7 in | 🌧 rainy |
| Rainy days | 20 days | |
| Humidity | 82% | 💦 very humid |
| Dew point | 24°C / 76°F | |
| Sunshine | 10.7 h/day | |
| Daylight | 12.2 h | |
| Wind | 16 km/h / 10 mph | |
| Air quality (US AQI) | 29 | 🍃 good |
Monthly averages from ERA5 reanalysis. AQI is the mean US Air Quality Index for the month.
Where is San Juan?
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San Juan in September — FAQ
- Is September a good time to visit San Juan?
- September in San Juan: sweltering, rainy, with clean air — a good time to visit. It ranks #12 of 12 months for San Juan on SeasonMap's comfort score (60/100).
- What is the weather like in San Juan in September?
- In September, San Juan averages a daily high of 31.5°C and a low of 25°C, with about 145.2 mm of rain over roughly 19.8 rainy days.
- What is the air quality in San Juan in September?
- San Juan has a mean US Air Quality Index of about 29 in September.