Sea temperature and swimming season in Cherbourg

The sea off Cherbourg never reaches 19.0°C. It peaks at 17.9°C in September and falls to 9.8°C in February. People do swim here — but in a wetsuit, or briefly, and knowing what they are doing.

"Warm enough" is a judgement, not a fact

There is no objective temperature at which the sea becomes swimmable. A Norwegian and a Spaniard will disagree, and neither is wrong. The season above uses 19.0°C — the bottom of the range most people describe as comfortable in swimwear — but here is what other thresholds imply:

If you are	Minimum	Months you can swim
Hardy	16.0°C	4 of 12
Most people	19.0°C	none
Prefer it warm	22.0°C	none
Prefer it hot	25.0°C	none

One threshold is not a preference. Below about 15.0°C cold shock becomes a genuine risk for anyone not acclimatised, and the sea here goes below that.

Month by month

Sea temperature, the air you climb out into, and the wind that decides how that feels.

Sea temperature, air temperature, wind and daylight by month.
Month	Sea	Air	Wind	Feels	What to wear
January	10.5°C	9.6°C ↓	7.4 m/s	Dangerous	5/4 mm with boots, gloves and hood
February	9.8°C	6.4°C ↓	6.7 m/s	Dangerous	5/4 mm with boots, gloves and hood
March	9.8°C	9.1°C ↓	5.7 m/s	Dangerous	5/4 mm with boots, gloves and hood
April	10.7°C	11.0°C	5.0 m/s	Dangerous	5/4 mm with boots, gloves and hood
May	12.5°C	14.0°C	5.3 m/s	Cold	4/3 mm with boots
June	14.6°C	16.7°C	4.4 m/s	Cold	4/3 mm with boots
July	16.6°C	18.8°C	5.2 m/s	Bracing	3/2 mm full suit
August	17.7°C	18.6°C	5.5 m/s	Bracing	3/2 mm full suit
September	17.9°C	16.9°C ↓	4.6 m/s	Bracing	3/2 mm full suit
October	16.5°C	15.6°C ↓	5.6 m/s	Bracing	3/2 mm full suit
November	14.6°C	12.1°C ↓	5.4 m/s	Cold	4/3 mm with boots
December	12.1°C	9.7°C ↓	6.7 m/s	Cold	4/3 mm with boots

Air is the average daily maximum — roughly what you would meet swimming in the middle of the day. An arrow marks months where the air is colder than the sea.

When in the day can you swim?

Daylight and burn risk by month, in Europe/Paris local time.

Month	Sunrise	Sunset	Daylight	Peak UV
January	08:57	17:34	8h 37m	0.7
February	08:16	18:25	10h 09m	1.6
March	07:19	19:10	11h 51m	3.0
April	07:14	20:58	13h 45m	4.9
May	06:21	21:43	15h 22m	6.4
June	05:58	22:15	16h 17m	7.2
July	06:15	22:09	15h 53m	7.3
August	06:57	21:24	14h 27m	6.3
September	07:42	20:20	12h 38m	4.4
October	08:27	19:16	10h 49m	2.4
November	08:18	17:23	9h 06m	1.0
December	08:56	17:06	8h 10m	0.6

Open water burns faster than a beach: the surface reflects sunlight up at you, and sunscreen washes off in the first few minutes. A long swim under a UV index above 6 needs a rash vest more than it needs more cream.

What the bands mean

From	Description	In practice
above 26°C	Bath-like	Warm enough that it offers no cooling at all
above 22°C	Very comfortable	Swimwear, no time limit for most people
above 19°C	Comfortable	Pleasant once you are in; most people swim happily
above 16°C	Bracing	Swimmable but short; many prefer a shorty wetsuit
above 12°C	Cold	Wetsuit territory. Unprotected swims should be brief
below 12°C	Dangerous	Cold shock risk. Specialist gear and supervision

Do you need a wetsuit in Cherbourg?

Some months, yes. The sea drops to 9.8°C in February. What thickness, month by month, for swimming and for surfing →

Other coastal cities in France

Where these numbers come from, and what they miss

Open water, not your beach. The measurement is a satellite cell about 28 km across, centred 18.7 km from Cherbourg. Shallow bays and lagoons run warmer; exposed coasts with upwelling run colder, sometimes by several degrees.
Surface temperature. Below a few metres the sea is often noticeably colder, and in summer a warm surface layer can sit over much colder water.
A six-year average, not a thirty-year normal. Sea temperature varies little between years, so this is close — but it is not a climate normal, and any individual year will differ.
Averages hide storms. A monthly mean says nothing about the week a cold current arrives.

Full methodology, sources and known limitations