The highest day temperature in September 2025 was 85°F. The lowest night temperature was 50°F. The average values for day and night temperatures during September were 74.6°F и 62.1°F respectivly.

The average sea surface temperature in September 2025 for Mystic was 70.2°F. The maximum and minimum values were 68.8°F and 73.2°F respectively.

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

Precipitation total in September for Mystic is 1.1 in. This value is relatively stable throughout the year.

The average wind speed in September is 7.7 mph. It makes September one of the most windless months of the year for Mystic.

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 Mystic in September is 7.5 hours.