Biak weather in September

In September, Biak sees average daytime highs of 28°C and overnight lows near 26°C, with 203 mm of rain across 24.5 wet days and about 12 hours of daylight. It is the 6th-warmest and 10th-wettest month of the year here.

Day-to-day highs hold fairly steady near 28°C through the month. The sky is clear or mostly clear about 18% of the time in September, and the air most often feels oppressive.

Daylight stretches from about 12 hours at the start of September to 12 hours by month's end. Set against the rest of the year, September is Biak's 2nd-clearest and 11th-windiest month. For the whole year in context, see Biak's year-round climate.

Daytime high: 28°; 6th warmest
Overnight low: 26°; 5th coldest
Rainfall: 203 mm; 24.5 wet days
Daylight: 12 hours; 5:50 AM – 5:50 PM
Cloud cover: 69%; 2nd clearest
Wind: 10 km/h; 11th windiest
Solar energy: 5.32 kWh/m²
Travel score: 4.1; out of 10

Biak is capital city of Biak Numfor Regency, Indonesia.

Air quality: WHO Ambient Air Quality Database. Density & description: Wikidata (CC0), GeoNames.

← August Biak year-round climate October →Best places to visit in September

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Temperature in September

Average highAverage lowShaded bands: 10–90% of days

Day-to-day highs hold fairly steady near 28°C through the month.

A typical September day in Biak reaches about 28°C in the afternoon and slips back to 26°C overnight — a 2°C spread between the day's warmth and the night's chill. On most days the high lands between 27°C and 29°C. Set against its neighbours, September runs on par with August and on par with October.

	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25	26	27	28	29	30
Avg high (°C)	28	28	28	28	28	28	28	28	28	28	28	28	28	28	28	28	28	28	28	28	28	28	28	28	28	28	28	28	28	28
Avg low (°C)	26	26	26	26	26	26	26	26	26	26	26	26	26	26	26	26	26	26	26	26	26	26	26	26	26	26	26	26	26	26

	Avg high (°C)	Avg low (°C)
1	28	26
2	28	26
3	28	26
4	28	26
5	28	26
6	28	26
7	28	26
8	28	26
9	28	26
10	28	26
11	28	26
12	28	26
13	28	26
14	28	26
15	28	26
16	28	26
17	28	26
18	28	26
19	28	26
20	28	26
21	28	26
22	28	26
23	28	26
24	28	26
25	28	26
26	28	26
27	28	26
28	28	26
29	28	26
30	28	26

How September really feels in Biak

Once humidity and wind are folded in, September averages 0 days that feel above 32°C and 0 that feel at or below 0°C — the comfort signal a plain temperature reading hides.

Days feeling ≥ 32°C

heat index over the day's high

Days feeling ≤ 0°C

wind chill below the day's low

September sits comfortably in between — no days that feel dangerously hot or drop to a hard freeze once humidity and wind are folded in.

Biak weather by month

How September compares with the rest of the year at a glance. September is the 6th-warmest and 10th-wettest month here — the current month is highlighted below.

Month	High / Low (°C)	Rainfall (mm)	Wet days	Daylight (hours)	Travel score
Jan	28° / 26°	229	27.5	12.1	3.6
Feb	28° / 26°	194	23.4	12	3.8
Mar	28° / 26°	238	27.8	12	3.6
Apr	28° / 26°	253	27.3	12	3.5
May	28° / 26°	223	26.9	11.9	3.6
Jun	28° / 26°	276	26.7	11.9	3.8
Jul	28° / 26°	249	26.1	11.9	4.0
Aug	28° / 26°	225	24.1	12	4.3
Sep	28° / 26°	203	24.5	12	4.1
Oct	28° / 26°	196	25.6	12	3.8
Nov	28° / 26°	211	26.1	12.1	3.5
Dec	28° / 26°	250	28.7	12.1	3.3

Cloud cover in September

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 18% of the time in September.

Beyond those clear spells, partly cloudy skies cover about 20% of September, with mostly cloudy or overcast conditions the remaining 62%.

	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25	26	27	28	29	30
Clearer (%)	35	34	34	34	35	34	34	35	36	36	37	37	38	38	38	39	40	40	40	40	40	40	40	40	40	40	40	39	38	38
Cloudier (%)	65	66	66	66	65	66	66	65	64	64	63	63	62	62	62	61	60	60	60	60	60	60	60	60	60	60	60	61	62	62

	Clearer (%)	Cloudier (%)
1	35	65
2	34	66
3	34	66
4	34	66
5	35	65
6	34	66
7	34	66
8	35	65
9	36	64
10	36	64
11	37	63
12	37	63
13	38	62
14	38	62
15	38	62
16	39	61
17	40	60
18	40	60
19	40	60
20	40	60
21	40	60
22	40	60
23	40	60
24	40	60
25	40	60
26	40	60
27	40	60
28	39	61
29	38	62
30	38	62

Chance of precipitation in September

Any precipitation

Biak gets around 203 mm of rain over 24.5 wet days in September. The line is the day-by-day chance of measurable precipitation.

Day to day, the chance of measurable rain averages around 82% and peaks near 84% on the wettest days.

	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25	26	27	28	29	30
Rain chance (%)	83	84	84	84	84	84	84	84	84	84	83	83	83	82	82	82	81	81	81	80	80	80	80	79	79	79	79	79	79	79

	Rain chance (%)
1	83
2	84
3	84
4	84
5	84
6	84
7	84
8	84
9	84
10	84
11	83
12	83
13	83
14	82
15	82
16	82
17	81
18	81
19	81
20	80
21	80
22	80
23	80
24	79
25	79
26	79
27	79
28	79
29	79
30	79

Humidity in September

DryComfortableHumidMuggyOppressiveMiserable

Most of September feels oppressive — the stacked bands show each day's mix of comfort levels, read off the dew point.

By dew point, September lands in the oppressive band about 77% of days. Sticky, muggy-or-worse air turns up on roughly 100% of them.

	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25	26	27	28	29	30
Oppressive (%)	84	84	84	84	84	84	84	84	84	84	84	83	83	82	81	80	79	78	76	75	73	72	71	69	68	67	67	66	65	65
Miserable (%)	16	16	16	16	16	16	16	16	16	16	16	17	17	18	19	20	21	22	24	25	27	28	29	31	32	33	33	34	35	35

	Oppressive (%)	Miserable (%)
1	84	16
2	84	16
3	84	16
4	84	16
5	84	16
6	84	16
7	84	16
8	84	16
9	84	16
10	84	16
11	84	16
12	83	17
13	83	17
14	82	18
15	81	19
16	80	20
17	79	21
18	78	22
19	76	24
20	75	25
21	73	27
22	72	28
23	71	29
24	69	31
25	68	32
26	67	33
27	67	33
28	66	34
29	65	35
30	65	35

Wind in September

Winds average 10 km/h in September.

Across September, daily wind ranges from about 10 km/h on the calmest days to 11 km/h at its breeziest. It stays fairly steady from day to day.

	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25	26	27	28	29	30
Wind speed (km/h)	10	10	10	10	10	10	10	10	10	10	10	10	10	10	10	10	10	10	10	11	11	11	11	11	11	11	11	11	11	11
Feels	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm

	Wind speed (km/h)	Feels
1	10	calm
2	10	calm
3	10	calm
4	10	calm
5	10	calm
6	10	calm
7	10	calm
8	10	calm
9	10	calm
10	10	calm
11	10	calm
12	10	calm
13	10	calm
14	10	calm
15	10	calm
16	10	calm
17	10	calm
18	10	calm
19	10	calm
20	11	calm
21	11	calm
22	11	calm
23	11	calm
24	11	calm
25	11	calm
26	11	calm
27	11	calm
28	11	calm
29	11	calm
30	11	calm

Sunrise & sunset in September

DaylightNight

Daylight runs from about 12 hours at the start of September to 12 hours by month's end. The lit band spans sunrise to sunset each day.

Days grow by about 0 minutes over September. Sunrise moves from 5:56 AM to 5:45 AM, and sunset from 5:55 PM to 5:45 PM.

	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25	26	27	28	29	30
Daylight (h)	12.0	12.0	12.0	12.0	12.0	12.0	12.0	12.0	12.0	12.0	12.0	12.0	12.0	12.0	12.0	12.0	12.0	12.0	12.0	12.0	12.0	12.0	12.0	12.0	12.0	12.0	12.0	12.0	12.0	12.0
Sunrise (AM)	5:56	5:56	5:55	5:55	5:55	5:54	5:54	5:53	5:53	5:53	5:52	5:52	5:51	5:51	5:51	5:50	5:50	5:49	5:49	5:49	5:48	5:48	5:47	5:47	5:47	5:46	5:46	5:45	5:45	5:45
Sunset (PM)	5:55	5:54	5:54	5:54	5:53	5:53	5:53	5:52	5:52	5:52	5:51	5:51	5:51	5:50	5:50	5:50	5:49	5:49	5:49	5:48	5:48	5:48	5:47	5:47	5:47	5:46	5:46	5:46	5:46	5:45

	Daylight (h)	Sunrise (AM)	Sunset (PM)
1	12.0	5:56	5:55
2	12.0	5:56	5:54
3	12.0	5:55	5:54
4	12.0	5:55	5:54
5	12.0	5:55	5:53
6	12.0	5:54	5:53
7	12.0	5:54	5:53
8	12.0	5:53	5:52
9	12.0	5:53	5:52
10	12.0	5:53	5:52
11	12.0	5:52	5:51
12	12.0	5:52	5:51
13	12.0	5:51	5:51
14	12.0	5:51	5:50
15	12.0	5:51	5:50
16	12.0	5:50	5:50
17	12.0	5:50	5:49
18	12.0	5:49	5:49
19	12.0	5:49	5:49
20	12.0	5:49	5:48
21	12.0	5:48	5:48
22	12.0	5:48	5:48
23	12.0	5:47	5:47
24	12.0	5:47	5:47
25	12.0	5:47	5:47
26	12.0	5:46	5:46
27	12.0	5:46	5:46
28	12.0	5:45	5:46
29	12.0	5:45	5:46
30	12.0	5:45	5:45

Solar energy in September

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in September, about 5.32 kWh/m².

For context, solar energy here swings from a low near 4.5 kWh/m² to a high of 5.48 kWh/m² in October across the year — September's 5.32 kWh/m² sits near the top of that range.

	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25	26	27	28	29	30
Solar energy (kWh/m²)	5.1	5.1	5.1	5.2	5.2	5.2	5.2	5.2	5.2	5.2	5.3	5.3	5.3	5.3	5.3	5.3	5.3	5.4	5.4	5.4	5.4	5.4	5.5	5.5	5.5	5.5	5.5	5.5	5.5	5.5
Level	Bright	Bright	Bright	Bright	Bright	Bright	Bright	Bright	Bright	Bright	Bright	Bright	Bright	Bright	Bright	Bright	Bright	Bright	Bright	Bright	Bright	Bright	Bright	Bright	Bright	Bright	Bright	Bright	Bright	Bright

	Solar energy (kWh/m²)	Level
1	5.1	Bright
2	5.1	Bright
3	5.1	Bright
4	5.2	Bright
5	5.2	Bright
6	5.2	Bright
7	5.2	Bright
8	5.2	Bright
9	5.2	Bright
10	5.2	Bright
11	5.3	Bright
12	5.3	Bright
13	5.3	Bright
14	5.3	Bright
15	5.3	Bright
16	5.3	Bright
17	5.3	Bright
18	5.4	Bright
19	5.4	Bright
20	5.4	Bright
21	5.4	Bright
22	5.4	Bright
23	5.5	Bright
24	5.5	Bright
25	5.5	Bright
26	5.5	Bright
27	5.5	Bright
28	5.5	Bright
29	5.5	Bright
30	5.5	Bright

Planning a trip in September

Is September a good time to visit Biak?

Our two travel scores rate September for general sightseeing and for beach or pool weather — 0 (poor) to 10 (ideal).

4.1

Sightseeing

2nd-best month of the year

4.4

Beach & pool

2nd-best month of the year

September is a reasonable time to visit Biak for sightseeing.

What to pack for Biak in September

From September's temperature range, rain chance, sun and wind — what's worth putting in the bag.

In September, Biak sees daytime highs around 28°C and nights near 26°C. Pack light clothes and rain gear. Worth having: sun protection. About 25 days see rain.

light clothesrain gearsun protection

Sea temperature near Biak in September

The nearest coast averages about 29°C in September — the other half of the beach question. The full-year curve and swim-comfort zones are below.

The sea offshore is warmest in November at about 30°C and coldest in March near 29°C.

The water stays above 20°C all year — warm enough for a swim any month.

	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Sea temperature (°C)	29	29	29	29	30	30	29	29	29	30	30	30
Comfort	Tropical	Tropical	Tropical	Tropical	Tropical	Tropical	Tropical	Tropical	Tropical	Tropical	Tropical	Tropical

	Sea temperature (°C)	Comfort
Jan	29	Tropical
Feb	29	Tropical
Mar	29	Tropical
Apr	29	Tropical
May	30	Tropical
Jun	30	Tropical
Jul	29	Tropical
Aug	29	Tropical
Sep	29	Tropical
Oct	30	Tropical
Nov	30	Tropical
Dec	30	Tropical

UV index in Biak in September

LowModerateHighVery highExtreme

Clear-sky midday UV in September peaks around 13 (very high — sun protection essential). The full-year curve, shaded by WHO exposure level, is below.

Under clear skies, the midday UV index in Biak peaks around March 17 at about 16 (extreme) — sunscreen, a hat and midday shade are essential. It bottoms out near June 18 at about 12 (extreme).

The index reaches 3 or more — the level where the WHO recommends sun protection — every month of the year.

	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
UV index (midday)	15	15	16	15	12	12	12	13	13	14	13	13
Level	Extreme	Extreme	Extreme	Extreme	Extreme	Extreme	Extreme	Extreme	Extreme	Extreme	Extreme	Extreme

	UV index (midday)	Level
Jan	15	Extreme
Feb	15	Extreme
Mar	16	Extreme
Apr	15	Extreme
May	12	Extreme
Jun	12	Extreme
Jul	12	Extreme
Aug	13	Extreme
Sep	13	Extreme
Oct	14	Extreme
Nov	13	Extreme
Dec	13	Extreme

Location & terrain

Where is Biak?

Biak sits at 1.2°S, 136.1°E, 10 m above sea level, in Indonesia. The nearest listed city is Ransiki, 216 km away.

Topography around Biak

How much the land rises and falls, and what covers it, within 3, 16 and 80 km of Biak.

Within 3 km, the terrain around Biak has only modest variations in elevation — a maximum elevation change of 169 m around an average of 23 m above sea level; within 16 km, only modest variations in elevation — a maximum elevation change of 219 m; within 80 km, very significant variations in elevation — a maximum elevation change of 1,442 m.

The land around Biak is covered by water (31%), trees (30%) and grassland (22%) within 3 km, water (52%) and trees (45%) within 16 km, and water (79%) and trees (21%) within 80 km.

3 km

169 m

water 31%

16 km

219 m

water 52%

80 km

1,442 m

water 79%

treesgrasslandartificial surfaceswater

← August Biak year-round climate October →Best places to visit in September

September weather nearby: Ransiki 216 km · Manokwari 227 km · Nabire 251 km · Bintuni 303 km · Mulia 353 km · Timika 388 km · Tiom 403 km · Teminabuan 453 km

Indonesia travel facts

Travel advisory: Level 2; Exercise Increased Caution
Power plugs: Type C / F; 230 V · 50 Hz
Prices: ≈ 29% of US; price level, 2025
GDP per capita: $5,060; 2025
Happiness: 5.6 / 10; World Happiness, 2025
Safe drinking water: 30%; of population, 2024
Homicide rate: 0.3; per 100k, 2022
Road deaths: 11.3; per 100k/yr, 2019
Income group: Upper middle; World Bank
English: Low; EF EPI 471
Religion

Sources: World Bank, US State Department, World Happiness Report, WHO/UNICEF, EF EPI, CIA World Factbook.

Data sources

Temperature, precipitation, cloud, humidity, wind and solar figures are a 1991–2020 climatology for Biak (-1.1767°, 136.082°, elevation 10 m), computed from hourly ERA5 reanalysis — contains modified Copernicus Climate Change Service information. Sun figures are astronomical calculations, not observations. City data © GeoNames, CC BY 4.0. Map outlines from Natural Earth (public domain); interactive map © Google. Sea temperatures are the NOAA OISST v2.1 1991–2020 monthly climatology (public domain), sampled at the nearest ocean point. UV index is derived from CAMS (Copernicus Atmosphere Monitoring Service) clear-sky UV data — contains modified Copernicus Atmosphere Monitoring Service information. Topography is sampled from the Copernicus DEM GLO-90 elevation model (© ESA/Airbus) and ESA WorldCover 2021 land cover (CC BY 4.0).

	Avg high (°C)	Avg low (°C)
1	28	26
2	28	26
3	28	26
4	28	26
5	28	26
6	28	26
7	28	26
8	28	26
9	28	26
10	28	26
11	28	26
12	28	26
13	28	26
14	28	26
15	28	26
16	28	26
17	28	26
18	28	26
19	28	26
20	28	26
21	28	26
22	28	26
23	28	26
24	28	26
25	28	26
26	28	26
27	28	26
28	28	26
29	28	26
30	28	26

	Clearer (%)	Cloudier (%)
1	35	65
2	34	66
3	34	66
4	34	66
5	35	65
6	34	66
7	34	66
8	35	65
9	36	64
10	36	64
11	37	63
12	37	63
13	38	62
14	38	62
15	38	62
16	39	61
17	40	60
18	40	60
19	40	60
20	40	60
21	40	60
22	40	60
23	40	60
24	40	60
25	40	60
26	40	60
27	40	60
28	39	61
29	38	62
30	38	62

	Rain chance (%)
1	83
2	84
3	84
4	84
5	84
6	84
7	84
8	84
9	84
10	84
11	83
12	83
13	83
14	82
15	82
16	82
17	81
18	81
19	81
20	80
21	80
22	80
23	80
24	79
25	79
26	79
27	79
28	79
29	79
30	79

	Oppressive (%)	Miserable (%)
1	84	16
2	84	16
3	84	16
4	84	16
5	84	16
6	84	16
7	84	16
8	84	16
9	84	16
10	84	16
11	84	16
12	83	17
13	83	17
14	82	18
15	81	19
16	80	20
17	79	21
18	78	22
19	76	24
20	75	25
21	73	27
22	72	28
23	71	29
24	69	31
25	68	32
26	67	33
27	67	33
28	66	34
29	65	35
30	65	35

	Avg high (°C)	Avg low (°C)
1	28	26
2	28	26
3	28	26
4	28	26
5	28	26
6	28	26
7	28	26
8	28	26
9	28	26
10	28	26
11	28	26
12	28	26
13	28	26
14	28	26
15	28	26
16	28	26
17	28	26
18	28	26
19	28	26
20	28	26
21	28	26
22	28	26
23	28	26
24	28	26
25	28	26
26	28	26
27	28	26
28	28	26
29	28	26
30	28	26

	Clearer (%)	Cloudier (%)
1	35	65
2	34	66
3	34	66
4	34	66
5	35	65
6	34	66
7	34	66
8	35	65
9	36	64
10	36	64
11	37	63
12	37	63
13	38	62
14	38	62
15	38	62
16	39	61
17	40	60
18	40	60
19	40	60
20	40	60
21	40	60
22	40	60
23	40	60
24	40	60
25	40	60
26	40	60
27	40	60
28	39	61
29	38	62
30	38	62

	Rain chance (%)
1	83
2	84
3	84
4	84
5	84
6	84
7	84
8	84
9	84
10	84
11	83
12	83
13	83
14	82
15	82
16	82
17	81
18	81
19	81
20	80
21	80
22	80
23	80
24	79
25	79
26	79
27	79
28	79
29	79
30	79

	Oppressive (%)	Miserable (%)
1	84	16
2	84	16
3	84	16
4	84	16
5	84	16
6	84	16
7	84	16
8	84	16
9	84	16
10	84	16
11	84	16
12	83	17
13	83	17
14	82	18
15	81	19
16	80	20
17	79	21
18	78	22
19	76	24
20	75	25
21	73	27
22	72	28
23	71	29
24	69	31
25	68	32
26	67	33
27	67	33
28	66	34
29	65	35
30	65	35

	Avg high (°C)	Avg low (°C)
1	28	26
2	28	26
3	28	26
4	28	26
5	28	26
6	28	26
7	28	26
8	28	26
9	28	26
10	28	26
11	28	26
12	28	26
13	28	26
14	28	26
15	28	26
16	28	26
17	28	26
18	28	26
19	28	26
20	28	26
21	28	26
22	28	26
23	28	26
24	28	26
25	28	26
26	28	26
27	28	26
28	28	26
29	28	26
30	28	26

	Clearer (%)	Cloudier (%)
1	35	65
2	34	66
3	34	66
4	34	66
5	35	65
6	34	66
7	34	66
8	35	65
9	36	64
10	36	64
11	37	63
12	37	63
13	38	62
14	38	62
15	38	62
16	39	61
17	40	60
18	40	60
19	40	60
20	40	60
21	40	60
22	40	60
23	40	60
24	40	60
25	40	60
26	40	60
27	40	60
28	39	61
29	38	62
30	38	62

	Rain chance (%)
1	83
2	84
3	84
4	84
5	84
6	84
7	84
8	84
9	84
10	84
11	83
12	83
13	83
14	82
15	82
16	82
17	81
18	81
19	81
20	80
21	80
22	80
23	80
24	79
25	79
26	79
27	79
28	79
29	79
30	79

	Oppressive (%)	Miserable (%)
1	84	16
2	84	16
3	84	16
4	84	16
5	84	16
6	84	16
7	84	16
8	84	16
9	84	16
10	84	16
11	84	16
12	83	17
13	83	17
14	82	18
15	81	19
16	80	20
17	79	21
18	78	22
19	76	24
20	75	25
21	73	27
22	72	28
23	71	29
24	69	31
25	68	32
26	67	33
27	67	33
28	66	34
29	65	35
30	65	35