Sea temperature and swimming season in Constitución

The sea off Constitución never reaches 19.0°C. It peaks at 14.5°C in February and falls to 12.1°C in August. 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	none
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	14.3°C	24.5°C	3.5 m/s	Cold	4/3 mm with boots
February	14.5°C	21.9°C	3.0 m/s	Cold	4/3 mm with boots
March	14.1°C	23.3°C	3.1 m/s	Cold	4/3 mm with boots
April	13.5°C	18.9°C	2.7 m/s	Cold	4/3 mm with boots
May	13.1°C	14.8°C	2.5 m/s	Cold	4/3 mm with boots
June	12.9°C	12.1°C ↓	2.5 m/s	Cold	4/3 mm with boots
July	12.4°C	12.5°C	3.3 m/s	Cold	4/3 mm with boots
August	12.1°C	13.9°C	2.8 m/s	Cold	4/3 mm with boots
September	12.2°C	14.7°C	2.7 m/s	Cold	4/3 mm with boots
October	12.2°C	16.6°C	3.1 m/s	Cold	4/3 mm with boots
November	12.9°C	20.1°C	3.4 m/s	Cold	4/3 mm with boots
December	13.3°C	21.7°C	3.3 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 America/Santiago local time.

Month	Sunrise	Sunset	Daylight	Peak UV
January	06:51	21:06	14h 16m	10.9
February	07:23	20:44	13h 21m	10.1
March	07:48	20:08	12h 19m	8.2
April	07:13	18:25	11h 11m	5.5
May	07:38	17:54	10h 16m	3.5
June	07:56	17:43	9h 47m	2.6
July	07:55	17:55	10h 00m	2.9
August	07:30	18:17	10h 48m	4.2
September	07:48	19:40	11h 52m	6.4
October	07:06	20:04	12h 58m	8.5
November	06:34	20:33	13h 59m	10.1
December	06:29	21:00	14h 31m	10.8

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 Constitución?

Some months, yes. The sea drops to 12.1°C in August. What thickness, month by month, for swimming and for surfing →

Other coastal cities in Chile

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 19.9 km from Constitución. 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