Iruma in Summer
In summer (June, July and August), Iruma sees average daytime highs around 26°C and overnight lows near 20°C, with 670 mm of rain over about 62 wet days across the season. It is the warmest season of the year and the wettest season of the year.
Over the season highs climb from about 22°C in early June to 27°C by late August. The sky is clear or mostly clear about 13% of the time across summer, and the air most often feels oppressive.
Summer is Iruma's 2nd-best season to visit on our travel score. For the whole year in context, see Iruma's year-round climate.
- Avg daytime high
- 26°C
- warmest season of the year
- Avg overnight low
- 20°C
- Rainfall
- 670 mm
- 62 wet days
- Avg wind
- 6 km/h
- Travel score
- 4.6
- 2nd-best season
- Months
- Jun · Jul · Aug
Temperature in Iruma in Summer
Over the season highs climb from about 22°C in early June to 27°C by late August.
A typical summer day in Iruma reaches about 26°C and drops to 20°C overnight. The warmest of the three months is August, the coolest June.
How summer really feels in Iruma
Once humidity and wind are folded in, summer brings about 0 days that feel above 32°C and 0 that feel at or below 0°C.
summer sits comfortably in between — no days that feel dangerously hot or drop to a hard freeze once humidity and wind are folded in.
Iruma weather by month
How the three summer months (June, July and August) compare with the rest of the year — the season's months are highlighted.
| Month | High / Low (°C) | Rainfall (mm) | Wet days | Snow days | Daylight (hours) | Travel score |
|---|---|---|---|---|---|---|
| Jan | 7° / -2° | 77 | 8.5 | 4.4 | 9.8 | 1.0 |
| Feb | 8° / -1° | 75 | 9.6 | 4.6 | 10.6 | 1.2 |
| Mar | 11° / 2° | 139 | 15.2 | 4.7 | 11.7 | 2.5 |
| Apr | 16° / 7° | 146 | 14.6 | 0.9 | 12.9 | 4.5 |
| May | 21° / 13° | 166 | 15.6 | 0 | 13.9 | 5.5 |
| Jun | 23° / 17° | 222 | 19.5 | 0 | 14.4 | 4.9 |
| Jul | 27° / 21° | 243 | 21.8 | 0 | 14.2 | 4.5 |
| Aug | 28° / 22° | 205 | 21 | 0 | 13.4 | 4.4 |
| Sep | 25° / 18° | 249 | 18.3 | 0 | 12.2 | 5.2 |
| Oct | 19° / 13° | 242 | 16.2 | 0 | 11.1 | 5.2 |
| Nov | 14° / 7° | 101 | 11.3 | 0.2 | 10.1 | 4.1 |
| Dec | 10° / 1° | 68 | 8.3 | 1.4 | 9.6 | 2.2 |
Cloud cover in Summer
The sky is clear or mostly clear about 13% of the time across summer.
Chance of precipitation in Summer
Iruma gets around 670 mm of rain over 62 wet days across summer. The line is the day-by-day chance of measurable precipitation.
Humidity in Summer
Most of summer feels oppressive — the stacked bands show each day's mix of comfort levels, read off the dew point.
Wind in Summer
Winds average 6 km/h across summer.
Sunrise & sunset in Summer
Daylight runs from about 14 h 12 min in early June to 12 h 48 min by late August. The lit band spans sunrise to sunset each day.
Solar energy in Summer
Average shortwave solar energy reaching the ground each day across summer, about 4.5 kWh/m².
Hazard calendar for Iruma
In summer, Iruma overlaps its pacific typhoon season. The full year is below, with each hazard's peak months called out.
Iruma sits in the Pacific typhoon belt; the season peaks July–October.
Is summer a good time to visit Iruma?
Our two travel scores rate summer for general sightseeing and for beach or pool weather — 0 (poor) to 10 (ideal), averaged across the three months.
summer is a reasonable time to visit Iruma for sightseeing.
What to pack for Iruma in Summer
From summer's temperature range, rain chance, sun and wind — what's worth putting in the bag.
In summer, Iruma sees daytime highs around 26°C and nights near 20°C. Pack light clothes and rain gear. Worth having: sun protection. About 62 days see rain.
Sea temperature near Iruma in Summer
The nearest coast averages about 23°C across summer — the other half of the beach question. The full-year curve and swim-comfort zones are below.
The sea at the nearest coast (about 51 km away) is warmest in August at about 26°C and coldest in February near 13°C.
It's comfortable for a long swim from Jun 7 to Nov 3 — about 4.9 months when the water holds above 20°C.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Sea temperature (°C) | 14 | 13 | 13 | 15 | 18 | 21 | 23 | 26 | 25 | 22 | 19 | 16 |
| Comfort | Bracing | Bracing | Bracing | Cool | Cool | Refreshing | Refreshing | Warm | Warm | Refreshing | Cool | Cool |
| Sea temperature (°C) | Comfort | |
|---|---|---|
| Jan | 14 | Bracing |
| Feb | 13 | Bracing |
| Mar | 13 | Bracing |
| Apr | 15 | Cool |
| May | 18 | Cool |
| Jun | 21 | Refreshing |
| Jul | 23 | Refreshing |
| Aug | 26 | Warm |
| Sep | 25 | Warm |
| Oct | 22 | Refreshing |
| Nov | 19 | Cool |
| Dec | 16 | Cool |
UV index in Iruma in Summer
Clear-sky midday UV across summer averages 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 Iruma peaks around July 15 at about 10 (very high) — sunscreen, a hat and midday shade are essential. It bottoms out near December 23 at about 2 (moderate).
The index reaches 3 or more — the level where the WHO recommends sun protection — in 10 months of the year.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| UV index (midday) | 2 | 4 | 4 | 7 | 8 | 9 | 10 | 9 | 8 | 6 | 3 | 2 |
| Level | Moderate | Moderate | Moderate | High | Very high | Very high | Very high | Very high | Very high | High | Moderate | Moderate |
| UV index (midday) | Level | |
|---|---|---|
| Jan | 2 | Moderate |
| Feb | 4 | Moderate |
| Mar | 4 | Moderate |
| Apr | 7 | High |
| May | 8 | Very high |
| Jun | 9 | Very high |
| Jul | 10 | Very high |
| Aug | 9 | Very high |
| Sep | 8 | Very high |
| Oct | 6 | High |
| Nov | 3 | Moderate |
| Dec | 2 | Moderate |
Air quality in Iruma in Summer
Average fine-particle pollution (PM2.5) through the year — so you can see where summer falls, not just the annual average.
Air quality in Iruma is worst in April — around 26 µg/m³ PM2.5 (moderate), about 1.9× the cleanest month (December, 14 µg/m³).
Modeled monthly averages (CAMS reanalysis, 2015–2024).
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| PM2.5 (µg/m³) | 15 | 21 | 25 | 26 | 24 | 20 | 17 | 16 | 16 | 16 | 16 | 14 |
| Level | Moderate | Moderate | Moderate | Moderate | Moderate | Moderate | Moderate | Moderate | Moderate | Moderate | Moderate | Moderate |
| PM2.5 (µg/m³) | Level | |
|---|---|---|
| Jan | 15 | Moderate |
| Feb | 21 | Moderate |
| Mar | 25 | Moderate |
| Apr | 26 | Moderate |
| May | 24 | Moderate |
| Jun | 20 | Moderate |
| Jul | 17 | Moderate |
| Aug | 16 | Moderate |
| Sep | 16 | Moderate |
| Oct | 16 | Moderate |
| Nov | 16 | Moderate |
| Dec | 14 | Moderate |
Where is Iruma?
Iruma sits at 35.8°N, 139.4°E, 126 m above sea level, in Japan. The nearest listed city is Sayama, 6.0 km away.
Topography around Iruma
How much the land rises and falls, and what covers it, within 3, 16 and 80 km of Iruma.
Within 3 km, the terrain around Iruma has only modest variations in elevation — a maximum elevation change of 140 m around an average of 124 m above sea level; within 16 km, large variations in elevation — a maximum elevation change of 725 m; within 80 km, extreme variations in elevation — a maximum elevation change of 3,737 m.
The land around Iruma is covered by artificial surfaces (53%) and trees (36%) within 3 km, artificial surfaces (49%) and trees (39%) within 16 km, and trees (46%) and artificial surfaces (28%) within 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
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 Iruma (35.818°, 139.368°, elevation 126 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.