The highest day temperature in December 2025 was 54°F. The lowest night temperature was 11°F. The average values for day and night temperatures during December were 36.0°F и 27.2°F respectivly.

The average sea surface temperature in December 2025 for Mystic was 45.9°F. The maximum and minimum values were 41.8°F and 50.2°F respectively.

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

Precipitation total in December for Mystic is 1.4 in. This value is relatively stable throughout the year.

The average wind speed in December is 10.3 mph. It makes December one of the most windy 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 December is 5.3 hours.