Arai weather in September

In September, Arai sees average daytime highs of 24°C and overnight lows near 17°C, with 204 mm of rain across 17.2 wet days and about 12.3 hours of daylight. It is the 3rd-warmest and 4th-wettest month of the year here.

Highs ease over the month, from about 26°C in the first days to 21°C by the end. The sky is clear or mostly clear about 16% of the time in September, and the air most often feels humid.

Daylight stretches from about 12 h 48 min at the start of September to 11 h 42 min by month's end. Set against the rest of the year, September is Arai's 8th-clearest and 9th-windiest month. For the whole year in context, see Arai's year-round climate.

Daytime high
24°
3rd warmest
Overnight low
17°
10th coldest
Rainfall
204 mm
17.2 wet days
Daylight
12 h 12 min
5:34 AM – 5:48 PM
Cloud cover
71%
8th clearest
Wind
6 km/h
9th windiest
Solar energy
3.9 kWh/m²
Travel score
5.4
out of 10

Temperature in September

Average highAverage lowShaded bands: 10–90% of days

Highs ease over the month, from about 26°C in the first days to 21°C by the end.

A typical September day in Arai reaches about 24°C in the afternoon and slips back to 17°C overnight — a 7°C spread between the day's warmth and the night's chill. On most days the high lands between 20°C and 28°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)
12620
22619
32619
42619
52619
62619
72519
82519
92518
102518
112518
122418
132418
142417
152417
162417
172317
182316
192316
202316
212316
222216
232215
242215
252215
262215
272114
282114
292114
302114

How September really feels in Arai

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.

Arai weather by month

How September compares with the rest of the year at a glance. September is the 3rd-warmest and 4th-wettest month here — the current month is highlighted below.

MonthHigh / Low (°C)Rainfall (mm)Wet daysSnow daysDaylight (hours)Travel score
Jan / -3°24225.423.59.70.0
Feb / -3°17920.918.410.60.0
Mar / -1°1622013.311.70.6
Apr13° / 11714.82.712.93.4
May19° / 10°130140145.6
Jun23° / 16°16616.5014.55.4
Jul26° / 20°24921.1014.34.8
Aug28° / 21°19119.7013.44.8
Sep24° / 17°20417.2012.35.4
Oct18° / 11°18816.40114.9
Nov12° / 16618.23.4102.5
Dec / -1°2272315.69.50.3

Cloud cover in September

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 16% of the time in September.

Beyond those clear spells, partly cloudy skies cover about 16% of September, with mostly cloudy or overcast conditions the remaining 68%.

0%25%50%75%100%151015202530
Clearer (%)Cloudier (%)
13367
23367
33367
43466
53466
63367
73367
83367
93367
103367
113367
123367
133367
143169
153268
163268
173169
183169
193169
203169
213169
223169
233169
243169
253169
263169
273169
283070
293070
303070

Chance of precipitation in September

Any precipitation

Arai gets around 204 mm of rain over 17.2 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 59% and peaks near 65% on the wettest days. The odds ease toward the end of the month.

0%20%40%60%80%151015202530
Rain chance (%)
165
265
365
465
564
664
764
863
963
1062
1161
1261
1360
1459
1558
1657
1756
1855
1954
2054
2154
2253
2353
2453
2554
2654
2754
2855
2955
3055

Humidity in September

DryComfortableHumidMuggyOppressiveMiserable

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

By dew point, September lands in the humid band about 29% of days. Sticky, muggy-or-worse air turns up on roughly 34% of them.

0%25%50%75%100%151015202530
Dry (%)Comfortable (%)Humid (%)Muggy (%)Oppressive (%)
106255118
206275116
307275115
418284914
519294912
6110304811
7111314610
821232459
921432438
1031533427
1141633406
1251834386
1361934365
1472134344
1592234314
16102434293
17122533263
18142733242
19152832222
20173032192
21193131171
22213330151
23233429141
24243627121
25263726101
2628382590
2729402370
2831412260
2933412150
3035421940

Wind in September

Winds average 6 km/h in September.

Across September, daily wind ranges from about 6 km/h on the calmest days to 7 km/h at its breeziest. It stays fairly steady from day to day.

0246810151015202530
Wind speed (km/h)Feels
16calm
26calm
36calm
46calm
56calm
66calm
76calm
86calm
96calm
106calm
116calm
126calm
136calm
146calm
156calm
166calm
176calm
186calm
196calm
206calm
216calm
226calm
236calm
246calm
256calm
267calm
277calm
287calm
297calm
307calm

Sunrise & sunset in September

DaylightNight

Daylight runs from about 12 h 48 min at the start of September to 11 h 42 min by month's end. The lit band spans sunrise to sunset each day.

Days shrink by about 66 minutes over September. Sunrise moves from 5:22 AM to 5:46 AM, and sunset from 6:12 PM to 5:26 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202530
Daylight (h)Sunrise (AM)Sunset (PM)
112.85:226:12
212.85:236:10
312.85:246:09
412.75:246:07
512.75:256:06
612.65:266:04
712.65:276:03
812.65:286:01
912.55:295:59
1012.55:295:58
1112.45:305:56
1212.45:315:55
1312.45:325:53
1412.35:335:52
1512.35:345:50
1612.25:345:48
1712.25:355:47
1812.25:365:45
1912.15:375:44
2012.15:385:42
2112.05:395:40
2212.05:405:39
2311.95:405:37
2411.95:415:36
2511.95:425:34
2611.85:435:33
2711.85:445:31
2811.75:455:29
2911.75:465:28
3011.75:465:26

Solar energy in September

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in September, about 3.9 kWh/m².

For context, solar energy here swings from a low near 2.02 kWh/m² to a high of 5.68 kWh/m² in May across the year — September's 3.9 kWh/m² falls in the middle.

012345151015202530
Solar energy (kWh/m²)Level
14.4Bright
24.4Bright
34.3Bright
44.3Bright
54.3Bright
64.2Bright
74.2Bright
84.1Bright
94.1Bright
104.0Bright
114.0Bright
124.0Moderate
133.9Moderate
143.9Moderate
153.9Moderate
163.8Moderate
173.8Moderate
183.8Moderate
193.8Moderate
203.7Moderate
213.7Moderate
223.7Moderate
233.6Moderate
243.6Moderate
253.6Moderate
263.6Moderate
273.5Moderate
283.5Moderate
293.5Moderate
303.5Moderate
Planning a trip in September

Hazard calendar for Arai

In seasonPeak

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

Arai 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 Arai?

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

5.4
Sightseeing
2nd-best month of the year
4.3
Beach & pool
3rd-best month of the year

September is a reasonable time to visit Arai for sightseeing.

What to pack for Arai in September

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

In September, Arai sees daytime highs around 24°C and nights near 17°C. Pack rain gear. Worth having: light clothes. About 17 days see rain.

rain gearlight clothes

Sea temperature near Arai in September

The nearest coast averages about 25°C in September — the other half of the beach question. The full-year curve and swim-comfort zones are below.

The sea at the nearest coast (about 16 km away) is warmest in August at about 27°C and coldest in March near 10°C.

It's comfortable for a long swim from Jun 20 to Nov 1 — about 4.4 months when the water holds above 20°C.

10°20°30°JanFebMarAprMayJunJulAugSepOctNovDecbracingcoolrefreshingwarmtropicalcomfortable to swim
Sea temperature (°C)Comfort
Jan13Bracing
Feb11Bracing
Mar10Bracing
Apr11Bracing
May15Bracing
Jun20Cool
Jul23Refreshing
Aug27Warm
Sep25Warm
Oct22Refreshing
Nov19Cool
Dec15Cool

UV index in Arai in September

LowModerateHighVery highExtreme

Clear-sky midday UV in September peaks around 9 (very high — sun protection essential). The full-year curve, shaded by WHO exposure level, is below.

Under clear skies, the midday UV index in Arai peaks around August 12 at about 10 (very high) — sunscreen, a hat and midday shade are essential. It bottoms out near January 1 at about 2 (moderate).

The index reaches 3 or more — the level where the WHO recommends sun protection — in 9 months of the year.

025710JanFebMarAprMayJunJulAugSepOctNovDecModerateHighVery highModerateAug 12UV 10Jan 1UV 2
UV index (midday)Level
Jan2Moderate
Feb4Moderate
Mar4Moderate
Apr7High
May8Very high
Jun9Very high
Jul9Very high
Aug10Very high
Sep9Very high
Oct5High
Nov3Moderate
Dec2Moderate

Air quality in Arai 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 Arai is worst in April — around 21 µg/m³ PM2.5 (moderate), about 2.2× the cleanest month (December, 10 µg/m³).

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

0102030JanFebMarAprMayJunJulAugSepOctNovDecGoodModerateGoodApr 1721 µg/m³Dec 1510 µg/m³
PM2.5 (µg/m³)Level
Jan11Good
Feb14Moderate
Mar20Moderate
Apr21Moderate
May20Moderate
Jun18Moderate
Jul15Moderate
Aug13Moderate
Sep12Good
Oct11Good
Nov11Good
Dec10Good
Location & terrain

Where is Arai?

Arai sits at 37.0°N, 138.2°E, 175 m above sea level, in Japan. The nearest listed city is Myoko, 4.0 km away.

Topography around Arai

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

Within 3 km, the terrain around Arai has significant variations in elevation — a maximum elevation change of 416 m around an average of 193 m above sea level; within 16 km, extreme variations in elevation — a maximum elevation change of 2,437 m; within 80 km, extreme variations in elevation — a maximum elevation change of 2,978 m.

The land around Arai is covered by trees (52%) and cropland (30%) within 3 km, trees (79%) within 16 km, and trees (60%) and water (29%) within 80 km.

3 km
416 m
16 km
2,437 m
80 km
2,978 m
treesgrasslandcroplandartificial surfacesbare terrainwater
September weather nearby: Myoko 4.0 km · Jōetsu 16 km · Iiyama 21 km · Nakano 31 km · Itoigawa 34 km · Nagano 39 km · Suzaka 40 km · Kashiwazaki 50 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 Arai (37.0006°, 138.2259°, elevation 175 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).