Castlerock — Water Temperature in December

Water Temperature Range

9°C

minimum

11°C

average

13°C

maximum

Get instant access to real-time water temperatures for this and all other locations with our iOS and Android apps.

Water Temperature Chart for Month

The chart shows the average daily water temperature for each day of the month based on historical data.

Table of Water Temperatures by Day of the Month for Previous Years

Day	2025	2024	2023	2022
DEC 1	12°C	12°C	11°C	12°C
DEC 2	12°C	11°C	11°C	12°C
DEC 3	12°C	12°C	12°C	12°C
DEC 4	12°C	11°C	12°C	12°C
DEC 5	12°C	11°C	11°C	12°C
DEC 6	12°C	11°C	11°C	12°C
DEC 7	12°C	11°C	12°C	12°C
DEC 8	11°C	11°C	11°C	11°C
DEC 9	11°C	11°C	11°C	11°C
DEC 10	11°C	10°C	11°C	11°C
DEC 11	11°C	10°C	11°C	11°C
DEC 12	11°C	11°C	11°C	11°C
DEC 13	12°C	11°C	11°C	12°C
DEC 14	11°C	10°C	11°C	11°C
DEC 15	11°C	10°C	10°C	11°C
DEC 16	11°C	11°C	10°C	11°C
DEC 17	11°C	11°C	10°C	10°C
DEC 18	10°C	11°C	9°C	10°C
DEC 19	11°C	11°C	10°C	10°C
DEC 20	11°C	11°C	10°C	10°C
DEC 21	11°C	11°C	10°C	10°C
DEC 22	11°C	11°C	10°C	11°C
DEC 23	10°C	10°C	10°C	10°C
DEC 24	10°C	10°C	9°C	10°C
DEC 25	10°C	10°C	9°C	10°C
DEC 26	10°C	10°C	9°C	10°C
DEC 27	10°C	11°C	9°C	11°C
DEC 28	10°C	10°C	9°C	11°C
DEC 29	11°C	11°C	9°C	11°C
DEC 30	10°C	10°C	9°C	11°C
DEC 31	10°C	10°C	9°C	11°C

December: Climate and Swimming Opportunities

Average Night Air Temperature

3°C

Average Day Air Temperature

8°C

Precipitation Amount per Month

121 mm

Number of Rainy Days

Daylight per Day

7 hrs

Sunshine per Day

1 hrs

Average Wind Speed

20 km/h

Average Humidity

91%

With such a ratio between the average monthly temperatures of water and air, swimming feels very cold and is only for cold-water enthusiasts. Most people will prefer just a brief splash, because warming up afterward can take time.