Rumoi weather in September

In September, Rumoi sees average daytime highs of 20°C and overnight lows near 14°C, with 137 mm of rain across 13.9 wet days and about 12.3 hours of daylight. It is the 3rd-warmest and 2nd-wettest month of the year here.

Highs ease over the month, from about 22°C in the first days to 18°C by the end. The sky is clear or mostly clear about 26% of the time in September, and the air most often feels dry.

Daylight stretches from about 13 h 06 min at the start of September to 11 h 36 min by month's end. Set against the rest of the year, September is Rumoi's 4th-clearest and 9th-windiest month. For the whole year in context, see Rumoi's year-round climate.

Daytime high
20°
3rd warmest
Overnight low
14°
10th coldest
Rainfall
137 mm
13.9 wet days
Daylight
12 h 18 min
5:19 AM – 5:37 PM
Cloud cover
63%
4th clearest
Wind
11 km/h
9th windiest
Solar energy
3.76 kWh/m²
Travel score
5.7
out of 10

Rumoi is city in Hokkaido, Japan.

Density
89/km²
people per km²
Founded
1947

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

Temperature in September

Average highAverage lowShaded bands: 10–90% of days

Highs ease over the month, from about 22°C in the first days to 18°C by the end.

A typical September day in Rumoi reaches about 20°C in the afternoon and slips back to 14°C overnight — a 6°C spread between the day's warmth and the night's chill. On most days the high lands between 17°C and 23°C. Set against its neighbours, September runs about 4°C cooler than August and about 6°C warmer than October.

10°15°20°25°30°151015202530
Avg high (°C)Avg low (°C)
12317
22317
32217
42216
52216
62216
72216
82216
92216
102115
112115
122115
132115
142114
152014
162014
172014
182014
192013
201913
211913
221913
231912
241912
251812
261812
271812
281811
291811
301711

How September really feels in Rumoi

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
0
heat index over the day's high
Days feeling ≤ C
0
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.

Rumoi weather by month

How September compares with the rest of the year at a glance. September is the 3rd-warmest and 2nd-wettest month here — the current month is highlighted below.

MonthHigh / Low (°C)Rainfall (mm)Wet daysSnow daysDaylight (hours)Travel score
Jan-3° / -9°6717.3219.10.0
Feb-2° / -8°5514.217.110.20.0
Mar / -5°6613.614.111.60.0
Apr / 6611.94.613.21.5
May14° / 7811.70.314.53.8
Jun18° / 12°7010.4015.25.6
Jul22° / 17°12112.4014.96.2
Aug24° / 18°14313.7013.86.2
Sep20° / 14°13713.9012.35.7
Oct14° / 11515.90.310.83.6
Nov / 12419.411.49.40.7
Dec-0° / -5°10221.622.68.80.0

Cloud cover in September

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 26% of the time in September.

Beyond those clear spells, partly cloudy skies cover about 17% of September, with mostly cloudy or overcast conditions the remaining 57%.

0%25%50%75%100%151015202530
Clearer (%)Cloudier (%)
14159
24159
34159
44060
54060
64060
74159
84159
94159
104159
114159
124258
134258
144258
154258
164357
174357
184456
194555
204555
214555
224555
234654
244654
254753
264753
274753
284852
294852
304753

Chance of precipitation in September

Any precipitation

Rumoi gets around 137 mm of rain over 13.9 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 46% and peaks near 49% on the wettest days.

0%20%40%60%151015202530
Rain chance (%)
145
245
345
445
545
645
745
845
945
1045
1145
1246
1346
1445
1545
1645
1745
1846
1946
2046
2147
2247
2348
2448
2549
2649
2749
2849
2949
3049

Humidity in September

DryComfortableHumidMuggyOppressiveMiserable

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

By dew point, September lands in the dry band about 42% of days. Sticky, muggy-or-worse air turns up on roughly 8% of them.

0%25%50%75%100%151015202530
Dry (%)Comfortable (%)Humid (%)Muggy (%)Oppressive (%)
1112541213
2122640193
3132739182
4152838172
5162937162
6183036152
7193134142
8213232132
9233331121
10253429111
11283427101
1230352681
1333352471
1436352271
1539342060
1642341850
1745341640
1848331540
1951331330
2054321130
2157311020
226030820
236229720
246528610
256826510
267025410
277323310
287522300
297820200
307919200

Wind in September

Winds average 11 km/h in September.

Across September, daily wind ranges from about 10 km/h on the calmest days to 12 km/h at its breeziest. It stays fairly steady from day to day.

051015151015202530
Wind speed (km/h)Feels
110calm
210calm
310calm
410calm
510calm
610calm
710calm
810calm
910calm
1010calm
1110calm
1210calm
1310calm
1410calm
1510calm
1611calm
1711calm
1811calm
1911calm
2011calm
2111calm
2211calm
2311calm
2411calm
2511calm
2611calm
2711calm
2811calm
2912calm
3012calm

Sunrise & sunset in September

DaylightNight

Daylight runs from about 13 h 06 min at the start of September to 11 h 36 min by month's end. The lit band spans sunrise to sunset each day.

Days shrink by about 90 minutes over September. Sunrise moves from 5:01 AM to 5:36 AM, and sunset from 6:05 PM to 5:10 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202530
Daylight (h)Sunrise (AM)Sunset (PM)
113.15:016:05
213.05:026:03
313.05:046:01
412.95:055:59
512.95:065:58
612.85:075:56
712.85:085:54
812.75:095:52
912.75:115:50
1012.65:125:48
1112.65:135:46
1212.55:145:44
1312.55:155:42
1412.45:165:41
1512.35:185:39
1612.35:195:37
1712.25:205:35
1812.25:215:33
1912.15:225:31
2012.15:245:29
2112.05:255:27
2212.05:265:25
2311.95:275:23
2411.95:285:21
2511.85:305:19
2611.85:315:17
2711.75:325:16
2811.75:335:14
2911.65:345:12
3011.65:365:10

Solar energy in September

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in September, about 3.76 kWh/m².

For context, solar energy here swings from a low near 1.43 kWh/m² to a high of 5.5 kWh/m² in May across the year — September's 3.76 kWh/m² falls in the middle.

012345151015202530
Solar energy (kWh/m²)Level
14.2Bright
24.2Bright
34.2Bright
44.1Bright
54.1Bright
64.1Bright
74.0Bright
84.0Moderate
94.0Moderate
103.9Moderate
113.9Moderate
123.9Moderate
133.8Moderate
143.8Moderate
153.8Moderate
163.7Moderate
173.7Moderate
183.7Moderate
193.6Moderate
203.6Moderate
213.6Moderate
223.5Moderate
233.5Moderate
243.5Moderate
253.5Moderate
263.4Moderate
273.4Moderate
283.4Moderate
293.3Moderate
303.3Moderate
Planning a trip in September

Hazard calendar for Rumoi

In seasonPeak

In September, Rumoi sits inside its pacific typhoon season. The full year is below, with each hazard's peak months called out.

Rumoi sits in the Pacific typhoon belt; the season peaks July–October.

Pacific typhoon
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec

Is September a good time to visit Rumoi?

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

5.7
Sightseeing
3rd-best month of the year
3.0
Beach & pool
3rd-best month of the year

September is a reasonable time to visit Rumoi for sightseeing.

What to pack for Rumoi in September

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

In September, Rumoi sees daytime highs around 20°C and nights near 14°C. Pack rain gear. About 14 days see rain.

rain gear

Sea temperature near Rumoi in September

The nearest coast averages about 21°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 August at about 21°C and coldest in February near 5°C.

It's comfortable for a long swim from Aug 3 to Sep 20 — about 1.6 months when the water holds above 20°C.

10°20°JanFebMarAprMayJunJulAugSepOctNovDecbracingcoolrefreshingwarm
Sea temperature (°C)Comfort
Jan6Bracing
Feb5Bracing
Mar5Bracing
Apr7Bracing
May10Bracing
Jun14Bracing
Jul18Cool
Aug21Refreshing
Sep21Refreshing
Oct17Cool
Nov13Bracing
Dec9Bracing

UV index in Rumoi in September

LowModerateHighVery highExtreme

Clear-sky midday UV in September peaks around 6 — enough to warrant sun protection. The full-year curve, shaded by WHO exposure level, is below.

Under clear skies, the midday UV index in Rumoi peaks around August 15 at about 8 (very high) — sunscreen, a hat and midday shade are essential. It bottoms out near December 20 at about 1 (low).

The index reaches 3 or more — the level where the WHO recommends sun protection — in 7 months of the year.

025710JanFebMarAprMayJunJulAugSepOctNovDecLowModerateHighHighVery highHighModerateLowAug 15UV 8Dec 20UV 1
UV index (midday)Level
Jan1Low
Feb2Low
Mar3Moderate
Apr5High
May7Very high
Jun7High
Jul7High
Aug8Very high
Sep6High
Oct4Moderate
Nov2Low
Dec1Low

Air quality in Rumoi in September

GoodModeratePoorUnhealthyVery unhealthy

Average fine-particle pollution (PM2.5) through the year — so you can see where September falls, not just the annual average.

Air quality in Rumoi is worst in April — around 17 µg/m³ PM2.5 (moderate), about 2.4× the cleanest month (December, 7 µg/m³).

Modeled monthly averages (CAMS reanalysis, 2015–2024).

01020JanFebMarAprMayJunJulAugSepOctNovDecGoodModerateGoodApr 1317 µg/m³Dec 217 µg/m³
PM2.5 (µg/m³)Level
Jan7Good
Feb10Good
Mar16Moderate
Apr17Moderate
May15Moderate
Jun10Good
Jul10Good
Aug8Good
Sep7Good
Oct9Good
Nov9Good
Dec7Good
Location & terrain

Where is Rumoi?

Rumoi sits at 43.9°N, 141.6°E, 35 m above sea level, in Japan. The nearest listed city is Fukagawa, 41 km away.

Topography around Rumoi

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

Within 3 km, the terrain around Rumoi has only modest variations in elevation — a maximum elevation change of 248 m around an average of 40 m above sea level; within 16 km, large variations in elevation — a maximum elevation change of 731 m; within 80 km, very significant variations in elevation — a maximum elevation change of 1,471 m.

The land around Rumoi is covered by trees (41%) and water (34%) within 3 km, trees (53%) and water (40%) within 16 km, and trees (51%) and water (35%) within 80 km.

3 km
248 m
16 km
731 m
80 km
1,471 m
treesgrasslandcroplandartificial surfaceswater
September weather nearby: Fukagawa 41 km · Takikawa 47 km · Sunagawa 54 km · Asahikawa 61 km · Minamishibetsuchō 63 km · Ashibetsu 64 km · Bibai 70 km · Nayoro 80 km

Japan travel facts

Travel advisory
Level 1
Exercise Normal Precautions
Power plugs
Type A / B
100 V · 50 / 60 Hz
Prices
≈ 65% of US
price level, 2025
GDP per capita
$35,951
2025
Happiness
6.1 / 10
World Happiness, 2025
Safe drinking water
99%
of population, 2024
Homicide rate
0.2
per 100k, 2023
Road deaths
3.6
per 100k/yr, 2019
Income group
High
World Bank
English
Very low
EF EPI 446
Religion
Shintoism 49%Buddhism 46%other 4%Christianity 1%

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 Rumoi (43.9344°, 141.6428°, elevation 35 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. Tropical-cyclone seasons are the published climatological basin seasons (NOAA National Hurricane Center / regional warning centres). 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. Monthly air-quality (PM2.5) seasonality is from the CAMS EAC4 reanalysis (Copernicus Atmosphere Monitoring Service), scaled to the WHO annual mean where available. Topography is sampled from the Copernicus DEM GLO-90 elevation model (© ESA/Airbus) and ESA WorldCover 2021 land cover (CC BY 4.0).