The highest day temperature in September 2025 was 85°F. The lowest night temperature was 60°F. The average values for day and night temperatures during September were 77.6°F и 61.9°F respectivly.

The average sea surface temperature in September 2025 for Alajuela was 87.5°F. The maximum and minimum values were 86.8°F and 88.0°F respectively.

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

Precipitation total in September for Alajuela is 21.9 in. It makes september one of the most rainy months of the year.

The average wind speed in September is 2.3 mph. It makes September the most windless month of the year for Alajuela.

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 Alajuela in September is 5.2 hours.