Sea temperature and swimming season in Jayapura

The sea off Jayapura is comfortable for swimming all year round — it never drops below 29.5°C, and peaks at 30.1°C in November.

"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	12 of 12
Most people	19.0°C	12 of 12
Prefer it warm	22.0°C	12 of 12
Prefer it hot	25.0°C	12 of 12

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	29.7°C	29.0°C ↓	2.0 m/s	Bath-like	none needed
February	29.5°C	29.1°C ↓	1.9 m/s	Bath-like	none needed
March	29.5°C	29.7°C	1.3 m/s	Bath-like	none needed
April	29.8°C	29.4°C ↓	1.3 m/s	Bath-like	none needed
May	30.1°C	29.4°C ↓	1.0 m/s	Bath-like	none needed
June	29.9°C	28.7°C ↓	1.0 m/s	Bath-like	none needed
July	29.5°C	28.0°C ↓	1.1 m/s	Bath-like	none needed
August	29.6°C	29.0°C ↓	1.4 m/s	Bath-like	none needed
September	29.7°C	28.7°C ↓	0.9 m/s	Bath-like	none needed
October	30.1°C	29.8°C ↓	1.1 m/s	Bath-like	none needed
November	30.1°C	29.8°C ↓	1.3 m/s	Bath-like	none needed
December	29.8°C	29.2°C ↓	1.3 m/s	Bath-like	none needed

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 Asia/Jayapura local time.

Month	Sunrise	Sunset	Daylight	Peak UV
January	05:38	17:53	12h 15m	14.8
February	05:45	17:56	12h 11m	16.2
March	05:42	17:49	12h 07m	16.9
April	05:35	17:38	12h 03m	15.9
May	05:33	17:33	12h 00m	14.2
June	05:38	17:36	11h 59m	13.1
July	05:43	17:42	11h 59m	13.5
August	05:40	17:42	12h 02m	15.2
September	05:29	17:35	12h 06m	16.6
October	05:18	17:27	12h 10m	16.6
November	05:14	17:28	12h 14m	15.3
December	05:24	17:40	12h 16m	14.3

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 Jayapura?

No. The sea here never falls below 29.5°C, so there is no month in which neoprene is the thing standing between you and a comfortable swim. A rash vest is worth having, but for the sun on your back rather than for warmth — the surface burns while you swim, and you will not feel it happening.

Other coastal cities in Indonesia

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 20.2 km from Jayapura. 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