The highest day temperature in September 2025 was 96°F. The lowest night temperature was 82°F. The average values for day and night temperatures during September were 89.9°F и 84.7°F respectivly.

The average sea surface temperature in September 2025 for San Juan was 89.7°F. The maximum and minimum values were 89.2°F and 90.4°F respectively.

Most of the days in September are cloudy but you can also expect sunny or gloomy days.

Precipitation total in September for San Juan is 3.0 in. It makes september one of the most rainy months of the year.

The average wind speed in September is 9.3 mph. It makes September one of the most windless months of the year for San Juan.

We are using day length and cloud cover information for each day of the month to calculate averages for this chart. Average sunny hours for San Juan in September is 6.8 hours.