The highest day temperature in September 2026 was 79°F. The lowest night temperature was 55°F. The average values for day and night temperatures during September were 70.1°F и 65.7°F respectivly.

The average sea surface temperature in September 2026 for Charlestown was 70.2°F. The maximum and minimum values were 63.6°F and 72.6°F respectively.

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

Precipitation total in September for Charlestown is 1.3 in. It makes september one of the most rainy months of the year.

The average wind speed in September is 10.4 mph. It makes September one of the most windless months of the year for Charlestown.

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 Charlestown in September is 7.2 hours.