Iida weather in September

In September, Iida sees average daytime highs of 23°C and overnight lows near 15°C, with 228 mm of rain across 15.5 wet days and about 12.2 hours of daylight. It is the 3rd-warmest and 3rd-wettest month of the year here.

Highs ease over the month, from about 25°C in the first days to 21°C by the end. The sky is clear or mostly clear about 22% 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 Iida's 8th-clearest and 11th-windiest month. For the whole year in context, see Iida's year-round climate.

Daytime high
23°
3rd warmest
Overnight low
15°
10th coldest
Rainfall
228 mm
15.5 wet days
Daylight
12 h 12 min
5:36 AM – 5:50 PM
Cloud cover
67%
8th clearest
Wind
5 km/h
11th windiest
Solar energy
4.02 kWh/m²
Travel score
5.7
out of 10

Iida is city in Nagano Prefecture, Japan.

Density
154/km²
people per km²
Founded
1937

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 25°C in the first days to 21°C by the end.

A typical September day in Iida reaches about 23°C in the afternoon and slips back to 15°C overnight — a 8°C spread between the day's warmth and the night's chill. On most days the high lands between 19°C and 26°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)
12517
22517
32517
42517
52517
62517
72517
82417
92416
102416
112416
122416
132416
142316
152315
162315
172315
182315
192315
202214
212214
222214
232214
242214
252113
262113
272113
282113
292113
302113

How September really feels in Iida

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.

Iida weather by month

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

MonthHigh / Low (°C)Rainfall (mm)Wet daysSnow daysDaylight (hours)Travel score
Jan / -7°9911.7119.90.0
Feb / -6°10710.28.110.70.0
Mar / -2°17113.1711.71.1
Apr14° / 17412.91.412.93.6
May19° / 19113.7013.85.4
Jun22° / 14°26318014.45.0
Jul25° / 18°30820.3014.25.0
Aug27° / 19°18418.6013.35.3
Sep23° / 15°22815.5012.25.7
Oct18° / 21012.9011.15.3
Nov11° / 12610.41.210.12.9
Dec / -3°100127.99.60.3

Cloud cover in September

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 22% 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 61%. Skies tend to open up as the month goes on.

0%25%50%75%100%151015202530
Clearer (%)Cloudier (%)
13961
24060
33961
43961
53862
63961
73961
83862
93961
103961
113862
123862
133961
143961
153961
163961
173862
183862
193862
203862
213862
223862
233862
243862
253862
263862
273862
283862
293862
303961

Chance of precipitation in September

Any precipitation

Iida gets around 228 mm of rain over 15.5 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 53% and peaks near 56% on the wettest days.

0%20%40%60%151015202530
Rain chance (%)
156
256
356
455
555
655
755
854
954
1054
1153
1253
1353
1452
1552
1651
1751
1851
1951
2051
2151
2251
2351
2450
2551
2651
2751
2851
2951
3051

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 36% of days. Sticky, muggy-or-worse air turns up on roughly 11% of them.

0%25%50%75%100%151015202530
Dry (%)Comfortable (%)Humid (%)Muggy (%)Oppressive (%)
131952251
242051241
342053221
452152211
562252200
662352190
772451180
882649170
992748160
10112847150
11122945140
12133044130
13153042120
14173141110
15193239100
1622323790
1724333580
1826333370
1929333160
2032342960
2134342750
2237342540
2339342340
2442342130
2544341930
2646341720
2748341620
2850341420
2952341310
3055331110

Wind in September

Winds average 5 km/h in September.

Across September, daily wind ranges from about 5 km/h on the calmest days to 5 km/h at its breeziest. It stays fairly steady from day to day.

0246810151015202530
Wind speed (km/h)Feels
15calm
25calm
35calm
45calm
55calm
65calm
75calm
85calm
95calm
105calm
115calm
125calm
135calm
145calm
155calm
165calm
175calm
185calm
195calm
205calm
215calm
225calm
235calm
245calm
255calm
265calm
275calm
285calm
295calm
305calm

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 5:25 AM to 5:48 AM, and sunset from 6:12 PM to 5:29 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202530
Daylight (h)Sunrise (AM)Sunset (PM)
112.85:256:12
212.75:266:11
312.75:266:09
412.75:276:08
512.65:286:06
612.65:296:05
712.65:296:03
812.55:306:02
912.55:316:00
1012.45:325:59
1112.45:335:57
1212.45:335:56
1312.35:345:54
1412.35:355:53
1512.35:365:51
1612.25:365:50
1712.25:375:48
1812.15:385:47
1912.15:395:45
2012.15:405:44
2112.05:405:42
2212.05:415:41
2312.05:425:39
2411.95:435:38
2511.95:435:36
2611.85:445:34
2711.85:455:33
2811.85:465:32
2911.75:475:30
3011.75:485:29

Solar energy in September

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in September, about 4.02 kWh/m².

For context, solar energy here swings from a low near 2.52 kWh/m² to a high of 5.47 kWh/m² in May across the year — September's 4.02 kWh/m² falls in the middle.

012345151015202530
Solar energy (kWh/m²)Level
14.5Bright
24.4Bright
34.4Bright
44.4Bright
54.3Bright
64.3Bright
74.3Bright
84.2Bright
94.2Bright
104.2Bright
114.1Bright
124.1Bright
134.1Bright
144.0Bright
154.0Bright
164.0Moderate
174.0Moderate
183.9Moderate
193.9Moderate
203.9Moderate
213.8Moderate
223.8Moderate
233.8Moderate
243.8Moderate
253.7Moderate
263.7Moderate
273.7Moderate
283.7Moderate
293.6Moderate
303.6Moderate
Planning a trip in September

Is September a good time to visit Iida?

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

5.7
Sightseeing
1st-best month of the year
4.4
Beach & pool
3rd-best month of the year

September is a reasonable time to visit Iida for sightseeing.

What to pack for Iida in September

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

In September, Iida sees daytime highs around 23°C and nights near 15°C. Pack rain gear. Worth having: light clothes. About 16 days see rain.

rain gearlight clothes

UV index in Iida in September

LowModerateHighVery highExtreme

Clear-sky midday UV in September peaks around 10 (very high — sun protection essential). The full-year curve, shaded by WHO exposure level, is below.

Under clear skies, the midday UV index in Iida peaks around July 13 at about 11 (extreme) — sunscreen, a hat and midday shade are essential. It bottoms out near December 20 at about 2 (moderate).

The index reaches 3 or more — the level where the WHO recommends sun protection — in 10 months of the year.

025710JanFebMarAprMayJunJulAugSepOctNovDecModerateHighVery highExtremeVery highModerateJul 13UV 11Dec 20UV 2
UV index (midday)Level
Jan3Moderate
Feb5Moderate
Mar6High
Apr7Very high
May9Very high
Jun10Extreme
Jul11Extreme
Aug9Very high
Sep10Very high
Oct6High
Nov4Moderate
Dec2Moderate

Air quality in Iida 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 Iida is worst in April — around 18 µg/m³ PM2.5 (moderate), about 2.4× the cleanest month (December, 8 µg/m³).

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

01020JanFebMarAprMayJunJulAugSepOctNovDecGoodModerateGoodApr 1818 µg/m³Dec 168 µg/m³
PM2.5 (µg/m³)Level
Jan9Good
Feb11Good
Mar16Moderate
Apr18Moderate
May17Moderate
Jun15Moderate
Jul11Good
Aug11Good
Sep10Good
Oct9Good
Nov8Good
Dec8Good
Location & terrain

Where is Iida?

Iida sits at 35.5°N, 137.8°E, 517 m above sea level, in Japan. The nearest listed city is Komagane, 24 km away.

Topography around Iida

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

Within 3 km, the terrain around Iida has large variations in elevation — a maximum elevation change of 733 m around an average of 565 m above sea level; within 16 km, very significant variations in elevation — a maximum elevation change of 2,037 m; within 80 km, extreme variations in elevation — a maximum elevation change of 3,167 m.

The land around Iida is covered by artificial surfaces (53%) and trees (36%) within 3 km, trees (86%) within 16 km, and trees (90%) within 80 km.

3 km
733 m
16 km
2,037 m
80 km
3,167 m
treesgrasslandcroplandartificial surfaceswater
September weather nearby: Komagane 24 km · Nakatsugawa 29 km · Ina 36 km · Ena 40 km · Minamiminowa 42 km · Kinoshita 45 km · Tatsuno 54 km · Mizunami 54 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 Iida (35.5196°, 137.8207°, elevation 517 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. 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).