Iwai weather in May

In May, Iwai sees average daytime highs of 21°C and overnight lows near 13°C, with 166 mm of rain across 15.6 wet days and about 13.9 hours of daylight. It is the 5th-warmest and 6th-wettest month of the year here.

Highs climb over the month, from about 19°C in the first days to 22°C by the end. The sky is clear or mostly clear about 20% of the time in May, and the air most often feels dry.

Daylight stretches from about 13 h 24 min at the start of May to 14 h 12 min by month's end. Set against the rest of the year, May is Iwai's 9th-clearest and 3rd-windiest month. For the whole year in context, see Iwai's year-round climate.

Daytime high
21°
5th warmest
Overnight low
13°
8th coldest
Rainfall
166 mm
15.6 wet days
Daylight
13 h 54 min
4:43 AM – 6:36 PM
Cloud cover
71%
9th clearest
Wind
7 km/h
3rd windiest
Solar energy
5.06 kWh/m²
Travel score
5.5
out of 10

Temperature in May

Average highAverage lowShaded bands: 10–90% of days

Highs climb over the month, from about 19°C in the first days to 22°C by the end.

A typical May day in Iwai reaches about 21°C in the afternoon and slips back to 13°C overnight — a 8°C spread between the day's warmth and the night's chill. On most days the high lands between 16°C and 25°C. Set against its neighbours, May runs about 4°C warmer than April and about 3°C cooler than June.

10°15°20°25°30°151015202531
Avg high (°C)Avg low (°C)
11910
21910
31911
41911
52011
62011
72011
82011
92012
102012
112012
122012
132012
142012
152112
162113
172113
182113
192113
202113
212113
222114
232114
242114
252214
262214
272214
282214
292214
302215
312215

How May really feels in Iwai

Once humidity and wind are folded in, May 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

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

Iwai weather by month

How May compares with the rest of the year at a glance. May is the 5th-warmest and 6th-wettest month here — the current month is highlighted below.

MonthHigh / Low (°C)Rainfall (mm)Wet daysSnow daysDaylight (hours)Travel score
Jan / -2°778.54.49.91.0
Feb / -1°759.64.610.61.2
Mar11° / 13915.24.711.72.5
Apr16° / 14614.60.912.94.5
May21° / 13°16615.6013.95.5
Jun23° / 17°22219.5014.44.9
Jul27° / 21°24321.8014.24.5
Aug28° / 22°20521013.44.4
Sep25° / 18°24918.3012.25.2
Oct19° / 13°24216.2011.15.2
Nov14° / 10111.30.210.14.1
Dec10° / 688.31.49.62.2

Cloud cover in May

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 20% of the time in May.

Beyond those clear spells, partly cloudy skies cover about 14% of May, with mostly cloudy or overcast conditions the remaining 67%. Skies tend to cloud over as the month goes on.

0%25%50%75%100%151015202531
Clearer (%)Cloudier (%)
14258
24159
34060
44060
54060
63763
73763
83664
93466
103367
113367
123268
133268
143268
153169
163169
173268
183268
193169
203169
213169
223169
233268
243169
253169
263169
273169
283070
293070
302872
312872

Chance of precipitation in May

Any precipitation

Iwai gets around 166 mm of rain over 15.6 wet days in May. The line is the day-by-day chance of measurable precipitation.

Day to day, the chance of measurable rain averages around 49% and peaks near 52% on the wettest days. The odds climb toward the end of the month.

0%20%40%60%151015202531
Rain chance (%)
144
244
344
445
546
646
747
848
949
1049
1150
1250
1351
1451
1551
1651
1751
1851
1951
2051
2151
2251
2351
2451
2551
2651
2751
2851
2951
3051
3152

Humidity in May

DryComfortableHumidMuggyOppressiveMiserable

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

By dew point, May lands in the dry band about 64% of days. It rarely turns muggy — the humid and sticky bands barely register.

0%25%50%75%100%151015202531
Dry (%)Comfortable (%)Humid (%)Muggy (%)
1851320
2841420
3831520
4821620
5801730
6791830
7771931
8762031
9742141
10742141
11722251
12722251
13702361
14702361
15682471
16672571
17652681
18652681
19622891
206029101
215830111
225631121
235433121
245234131
254936141
264737141
274539151
284240161
294042172
303743182
313444202

Wind in May

Winds average 7 km/h in May.

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

0246810151015202531
Wind speed (km/h)Feels
17calm
27calm
37calm
47calm
57calm
67calm
77calm
87calm
97calm
107calm
117calm
127calm
137calm
147calm
157calm
167calm
177calm
187calm
197calm
207calm
217calm
227calm
237calm
247calm
257calm
267calm
277calm
287calm
297calm
307calm
317calm

Sunrise & sunset in May

DaylightNight

Daylight runs from about 13 h 24 min at the start of May to 14 h 12 min by month's end. The lit band spans sunrise to sunset each day.

Days grow by about 48 minutes over May. Sunrise moves from 4:57 AM to 4:34 AM, and sunset from 6:23 PM to 6:47 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202531
Daylight (h)Sunrise (AM)Sunset (PM)
113.44:576:23
213.54:566:24
313.54:556:25
413.54:546:26
513.64:536:27
613.64:526:27
713.64:516:28
813.74:506:29
913.74:496:30
1013.74:486:31
1113.74:476:32
1213.84:466:33
1313.84:456:33
1413.84:446:34
1513.94:446:35
1613.94:436:36
1713.94:426:37
1813.94:416:37
1914.04:416:38
2014.04:406:39
2114.04:396:40
2214.04:396:41
2314.14:386:41
2414.14:376:42
2514.14:376:43
2614.14:366:44
2714.14:366:44
2814.24:356:45
2914.24:356:46
3014.24:346:46
3114.24:346:47

Solar energy in May

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in May, about 5.06 kWh/m² — the sunniest month for solar.

For context, solar energy here swings from a low near 2.39 kWh/m² to a high of 5.06 kWh/m² in May across the year — May's 5.06 kWh/m² sits near the top of that range.

0246151015202531
Solar energy (kWh/m²)Level
15.1Bright
25.1Bright
35.1Bright
45.1Bright
55.1Bright
65.1Bright
75.1Bright
85.1Bright
95.0Bright
105.0Bright
115.0Bright
125.0Bright
135.0Bright
145.0Bright
155.0Bright
165.0Bright
175.0Bright
185.1Bright
195.1Bright
205.1Bright
215.1Bright
225.1Bright
235.1Bright
245.1Bright
255.1Bright
265.1Bright
275.1Bright
285.0Bright
295.0Bright
305.0Bright
315.0Bright
Planning a trip in May

Hazard calendar for Iwai

In seasonPeak

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

Iwai 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 May a good time to visit Iwai?

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

5.5
Sightseeing
1st-best month of the year
3.1
Beach & pool
5th-best month of the year

May is a reasonable time to visit Iwai for sightseeing.

What to pack for Iwai in May

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

In May, Iwai sees daytime highs around 21°C and nights near 13°C. Pack rain gear. Worth having: sun protection. About 16 days see rain.

rain gearsun protection

Sea temperature near Iwai in May

The nearest coast averages about 18°C in May — the other half of the beach question. The full-year curve and swim-comfort zones are below.

The sea at the nearest coast (about 60 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.

10°15°20°25°JanFebMarAprMayJunJulAugSepOctNovDecbracingcoolrefreshingwarmtropicalcomfortable to swim
Sea temperature (°C)Comfort
Jan14Bracing
Feb13Bracing
Mar13Bracing
Apr15Cool
May18Cool
Jun21Refreshing
Jul23Refreshing
Aug26Warm
Sep25Warm
Oct22Refreshing
Nov19Cool
Dec16Cool

UV index in Iwai in May

LowModerateHighVery highExtreme

Clear-sky midday UV in May 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 Iwai peaks around July 16 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.

025710JanFebMarAprMayJunJulAugSepOctNovDecModerateHighVery highModerateJul 16UV 10Dec 23UV 2
UV index (midday)Level
Jan2Moderate
Feb4Moderate
Mar5Moderate
Apr7High
May9Very high
Jun9Very high
Jul10Very high
Aug9Very high
Sep9Very high
Oct6High
Nov4Moderate
Dec2Moderate

Air quality in Iwai in May

GoodModeratePoorUnhealthyVery unhealthy

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

Air quality in Iwai 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).

0102030JanFebMarAprMayJunJulAugSepOctNovDecModerateApr 1426 µg/m³Dec 1814 µg/m³
PM2.5 (µg/m³)Level
Jan15Moderate
Feb21Moderate
Mar25Moderate
Apr26Moderate
May24Moderate
Jun20Moderate
Jul17Moderate
Aug16Moderate
Sep16Moderate
Oct16Moderate
Nov16Moderate
Dec14Moderate
Location & terrain

Where is Iwai?

Iwai sits at 35.8°N, 139.2°E, 321 m above sea level, in Japan. The nearest listed city is Akiruno, 2.0 km away.

Topography around Iwai

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

Within 3 km, the terrain around Iwai has significant variations in elevation — a maximum elevation change of 387 m around an average of 279 m above sea level; within 16 km, very significant variations in elevation — a maximum elevation change of 1,339 m; within 80 km, extreme variations in elevation — a maximum elevation change of 3,737 m.

The land around Iwai is covered by trees (82%) within 3 km, trees (73%) and artificial surfaces (22%) within 16 km, and trees (48%) and artificial surfaces (27%) within 80 km.

3 km
387 m
16 km
1,339 m
80 km
3,737 m
treesgrasslandcroplandartificial surfacesbare terrainwater
May weather nearby: Akiruno 2.0 km · Itsukaichi 3.0 km · Ōme 4.0 km · Hamura 8.0 km · Fussa 8.0 km · Hakonegasaki 11 km · Hachiōji 13 km · Yokota 14 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 Iwai (35.75°, 139.2333°, elevation 321 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).