Kosai in Spring
In spring (March, April and May), Kosai sees average daytime highs around 19°C and overnight lows near 10°C, with 457 mm of rain over about 32 wet days across the season. It is the 3rd-warmest season and the 3rd-wettest season.
Over the season highs climb from about 13°C in early March to 25°C by late May. The sky is clear or mostly clear about 35% of the time across spring, and the air most often feels dry.
Spring is Kosai's 2nd-best season to visit on our travel score. For the whole year in context, see Kosai's year-round climate.
- Avg daytime high
- 19°C
- 3rd-warmest season
- Avg overnight low
- 10°C
- Rainfall
- 457 mm
- 32 wet days
- Avg wind
- 14 km/h
- Travel score
- 5.6
- 2nd-best season
- Months
- Mar · Apr · May
Temperature in Kosai in Spring
Over the season highs climb from about 13°C in early March to 25°C by late May.
A typical spring day in Kosai reaches about 19°C and drops to 10°C overnight. The warmest of the three months is May, the coolest March.
How spring really feels in Kosai
Once humidity and wind are folded in, spring brings about 0 days that feel above 32°C and 0 that feel at or below 0°C.
spring sits comfortably in between — no days that feel dangerously hot or drop to a hard freeze once humidity and wind are folded in.
Kosai weather by month
How the three spring months (March, April and May) compare with the rest of the year — the season's months are highlighted.
| Month | High / Low (°C) | Rainfall (mm) | Wet days | Daylight (hours) | Travel score |
|---|---|---|---|---|---|
| Jan | 10° / 3° | 65 | 5.8 | 9.9 | 2.6 |
| Feb | 11° / 3° | 81 | 6.8 | 10.7 | 3.0 |
| Mar | 14° / 6° | 135 | 10.5 | 11.7 | 4.3 |
| Apr | 19° / 11° | 151 | 10.4 | 12.8 | 6.0 |
| May | 23° / 15° | 170 | 11.3 | 13.8 | 6.5 |
| Jun | 26° / 20° | 242 | 15.6 | 14.3 | 5.4 |
| Jul | 30° / 24° | 250 | 15.8 | 14.1 | 4.2 |
| Aug | 31° / 25° | 144 | 15.3 | 13.3 | 3.8 |
| Sep | 28° / 22° | 236 | 14.6 | 12.2 | 5.2 |
| Oct | 23° / 16° | 211 | 11.8 | 11.1 | 6.6 |
| Nov | 18° / 10° | 113 | 8.9 | 10.2 | 5.9 |
| Dec | 12° / 5° | 67 | 6.3 | 9.7 | 3.9 |
Cloud cover in Spring
The sky is clear or mostly clear about 35% of the time across spring.
Chance of precipitation in Spring
Kosai gets around 457 mm of rain over 32 wet days across spring. The line is the day-by-day chance of measurable precipitation.
Humidity in Spring
Most of spring feels dry — the stacked bands show each day's mix of comfort levels, read off the dew point.
Wind in Spring
Winds average 14 km/h across spring.
Sunrise & sunset in Spring
Daylight runs from about 11 h 12 min in early March to 14 h 06 min by late May. The lit band spans sunrise to sunset each day.
Solar energy in Spring
Average shortwave solar energy reaching the ground each day across spring, about 5.0 kWh/m².
Hazard calendar for Kosai
In spring, Kosai overlaps its pacific typhoon season. The full year is below, with each hazard's peak months called out.
Kosai sits in the Pacific typhoon belt; the season peaks July–October.
Is spring a good time to visit Kosai?
Our two travel scores rate spring for general sightseeing and for beach or pool weather — 0 (poor) to 10 (ideal), averaged across the three months.
spring is a reasonable time to visit Kosai for sightseeing.
What to pack for Kosai in Spring
From spring's temperature range, rain chance, sun and wind — what's worth putting in the bag.
In spring, Kosai sees daytime highs around 19°C and nights near 10°C. Worth packing: light clothes, a warm layer, rain gear and sun protection. About 32 days see rain.
Sea temperature near Kosai in Spring
The nearest coast averages about 17°C across spring — the other half of the beach question. The full-year curve and swim-comfort zones are below.
The sea at the nearest coast (about 13 km away) is warmest in August at about 27°C and coldest in February near 16°C.
It's comfortable for a long swim from May 25 to Nov 28 — about 6.2 months when the water holds above 20°C.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Sea temperature (°C) | 16 | 16 | 16 | 17 | 19 | 22 | 25 | 27 | 26 | 23 | 21 | 19 |
| Comfort | Cool | Cool | Cool | Cool | Cool | Refreshing | Warm | Warm | Warm | Refreshing | Refreshing | Cool |
| Sea temperature (°C) | Comfort | |
|---|---|---|
| Jan | 16 | Cool |
| Feb | 16 | Cool |
| Mar | 16 | Cool |
| Apr | 17 | Cool |
| May | 19 | Cool |
| Jun | 22 | Refreshing |
| Jul | 25 | Warm |
| Aug | 27 | Warm |
| Sep | 26 | Warm |
| Oct | 23 | Refreshing |
| Nov | 21 | Refreshing |
| Dec | 19 | Cool |
UV index in Kosai in Spring
Clear-sky midday UV across spring averages around 7 — enough to warrant sun protection. The full-year curve, shaded by WHO exposure level, is below.
Under clear skies, the midday UV index in Kosai peaks around July 15 at about 10 (very high) — sunscreen, a hat and midday shade are essential. It bottoms out near December 22 at about 3 (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) | 3 | 4 | 5 | 7 | 9 | 10 | 10 | 9 | 9 | 6 | 4 | 3 |
| Level | Moderate | Moderate | Moderate | High | Very high | Very high | Very high | Very high | Very high | High | Moderate | Moderate |
| UV index (midday) | Level | |
|---|---|---|
| Jan | 3 | Moderate |
| Feb | 4 | Moderate |
| Mar | 5 | Moderate |
| Apr | 7 | High |
| May | 9 | Very high |
| Jun | 10 | Very high |
| Jul | 10 | Very high |
| Aug | 9 | Very high |
| Sep | 9 | Very high |
| Oct | 6 | High |
| Nov | 4 | Moderate |
| Dec | 3 | Moderate |
Air quality in Kosai in Spring
Average fine-particle pollution (PM2.5) through the year — so you can see where spring falls, not just the annual average.
Air quality in Kosai is worst in April — around 25 µg/m³ PM2.5 (moderate), about 1.6× the cleanest month (July, 15 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) | 17 | 19 | 25 | 25 | 24 | 20 | 15 | 15 | 16 | 18 | 18 | 16 |
| Level | Moderate | Moderate | Moderate | Moderate | Moderate | Moderate | Moderate | Moderate | Moderate | Moderate | Moderate | Moderate |
| PM2.5 (µg/m³) | Level | |
|---|---|---|
| Jan | 17 | Moderate |
| Feb | 19 | Moderate |
| Mar | 25 | Moderate |
| Apr | 25 | Moderate |
| May | 24 | Moderate |
| Jun | 20 | Moderate |
| Jul | 15 | Moderate |
| Aug | 15 | Moderate |
| Sep | 16 | Moderate |
| Oct | 18 | Moderate |
| Nov | 18 | Moderate |
| Dec | 16 | Moderate |
Where is Kosai?
Kosai sits at 34.7°N, 137.5°E, 30 m above sea level, in Japan. The nearest listed city is Arai, 4.0 km away.
Topography around Kosai
How much the land rises and falls, and what covers it, within 3, 16 and 80 km of Kosai.
Within 3 km, the terrain around Kosai has only modest variations in elevation — a maximum elevation change of 83 m around an average of 33 m above sea level; within 16 km, significant variations in elevation — a maximum elevation change of 463 m; within 80 km, very significant variations in elevation — a maximum elevation change of 2,300 m.
The land around Kosai is covered by trees (41%) and artificial surfaces (31%) within 3 km, water (47%) and trees (25%) within 16 km, and water (43%) and trees (42%) 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 Kosai (34.7005°, 137.5225°, elevation 30 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.