Climate averages 1991–2020
San Juan weather
in September.
A hot, wet month: the 4th warmest and the wettest of the year.
Long-term climate patterns, not a forecast for a particular trip.
September is a hot month in San Juan: daytime highs average 31.2°C and nights cool to about 24.5°C. By daytime temperature it is the 4th warmest of the 12 months.
Expect about 131 mm of rain on roughly 21 days, which makes September a wet month (the wettest month of the year). Daylight, from sunrise to sunset, lasts about 12 h 15 min on an average September day.
The nearest other city in this atlas is Bayamón (9 km away). In September its highs average 31.1°C, about as warm as San Juan, with 122 mm of rain.
Among the 7 cities listed in Puerto Rico, San Juan ranks joint 1st of 7 for the warmest September highs and joint 4th of 7 for the driest September (rainfall, lowest first). The mean September high of those 7 cities is 30.7°C; San Juan is 0.5°C warmer than that mean.
From September to October, average highs fall by 0.8°C to 30.4°C, and monthly rainfall falls from 131 mm to 124 mm.
The annual picture
September in context
Monthly rainfall
Average total · mmAverages from hourly ERA5 reanalysis data. Actual weather varies from year to year. How these numbers are calculated
Every month, side by side
San Juan climate table
| Month | Average highHigh / low | Average low | Rainfall mm/month | Rain days ≥1 mm/day | Daylight hours/dayDaylight h/day |
|---|---|---|---|---|---|
| January | 28.0°C21.5°C | 21.5°C | 39 | 10.4 | 11.211 h |
| February | 28.6°C21.3°C | 21.3°C | 29 | 7.7 | 11.512 h |
| March | 29.3°C21.5°C | 21.5°C | 39 | 8.4 | 12.012 h |
| April | 30.0°C22.3°C | 22.3°C | 72 | 11.0 | 12.613 h |
| May | 30.4°C23.4°C | 23.4°C | 112 | 16.1 | 13.013 h |
| June | 31.3°C24.3°C | 24.3°C | 68 | 13.8 | 13.213 h |
| July | 31.5°C24.6°C | 24.6°C | 80 | 16.4 | 13.113 h |
| August | 31.5°C24.7°C | 24.7°C | 95 | 18.7 | 12.813 h |
| September, selected | 31.2°C24.5°C | 24.5°C | 131 | 20.8 | 12.312 h |
| October | 30.4°C24.1°C | 24.1°C | 124 | 20.5 | 11.712 h |
| November | 28.9°C23.2°C | 23.2°C | 112 | 18.2 | 11.311 h |
| December | 28.1°C22.1°C | 22.1°C | 48 | 12.2 | 11.011 h |
Rainfall is the average of the 30 separate monthly totals. A rain day is a local calendar day with at least 1 mm of precipitation. Daylight is the calculated sunrise-to-sunset length, not measured sunshine.
Compare places
September in nearby cities
- Bayamón in SeptemberPuerto Rico · 9 kmHigh 31.1°C · Low 24.6°C · 122 mm rain
- Carolina in SeptemberPuerto Rico · 18 kmHigh 30.9°C · Low 24.6°C · 131 mm rain
- Caguas in SeptemberPuerto Rico · 27 kmHigh 30.1°C · Low 24.6°C · 168 mm rain
- Arecibo in SeptemberPuerto Rico · 64 kmHigh 31.2°C · Low 24.4°C · 154 mm rain
- Ponce in SeptemberPuerto Rico · 75 kmHigh 29.7°C · Low 24.5°C · 124 mm rain
- Mayagüez in SeptemberPuerto Rico · 113 kmHigh 30.6°C · Low 25.6°C · 98 mm rain
- Punta Cana in SeptemberDominican Republic · 243 kmHigh 28.9°C · Low 26.0°C · 121 mm rain
- Salvaleón de Higüey in SeptemberDominican Republic · 275 kmHigh 30.2°C · Low 24.2°C · 107 mm rain
Read the numbers correctly
Climate, not a promise.
These patterns help compare months. They cannot tell you the weather on a specific day of your trip.
Sources, method and limitsHow these numbers are made (what the highs, lows and rain days mean, the sources and the model cell used for San Juan) is explained once on the San Juan year overview and on the Sources, method and limits page.
Carolina lies in the same rainfall cell, so its rainfall figures are identical to these; temperatures differ because they come from smaller 0.1° cells.