Sea temperature and swimming season in Pori

The sea off Pori never reaches 19.0°C. It peaks at 17.7°C in August and falls to 0.3°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	2 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	1.6°C	-0.1°C ↓	4.6 m/s	Dangerous	6/5 mm and a very good reason
February	0.3°C	0.7°C	3.6 m/s	Dangerous	6/5 mm and a very good reason
March	0.8°C	2.6°C	3.8 m/s	Dangerous	6/5 mm and a very good reason
April	2.4°C	6.7°C	4.0 m/s	Dangerous	6/5 mm and a very good reason
May	7.5°C	15.1°C	2.7 m/s	Dangerous	6/5 mm and a very good reason
June	13.7°C	16.2°C	2.8 m/s	Cold	4/3 mm with boots
July	17.2°C	23.2°C	3.3 m/s	Bracing	3/2 mm full suit
August	17.7°C	19.3°C	3.3 m/s	Bracing	3/2 mm full suit
September	14.3°C	15.2°C	3.0 m/s	Cold	4/3 mm with boots
October	10.8°C	9.2°C ↓	3.6 m/s	Dangerous	5/4 mm with boots, gloves and hood
November	7.5°C	3.8°C ↓	4.5 m/s	Dangerous	6/5 mm and a very good reason
December	3.8°C	-1.2°C ↓	3.4 m/s	Dangerous	6/5 mm and a very good reason

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/Helsinki local time.

Month	Sunrise	Sunset	Daylight	Peak UV
January	09:32	15:51	6h 19m	0.1
February	08:16	17:17	9h 01m	0.4
March	06:49	18:33	11h 44m	1.2
April	06:11	20:54	14h 44m	2.5
May	04:43	22:15	17h 32m	3.8
June	03:50	23:16	19h 26m	4.6
July	04:21	22:55	18h 34m	4.5
August	05:40	21:34	15h 55m	3.6
September	06:59	19:56	12h 58m	2.0
October	08:15	18:21	10h 06m	0.7
November	08:40	15:54	7h 14m	0.1
December	09:45	15:10	5h 25m	0.0

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 Pori?

Some months, yes. The sea drops to 0.3°C in February. What thickness, month by month, for swimming and for surfing →

Other coastal cities in Finland

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 24.8 km from Pori. 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