Kosai in Fall
In fall (September, October and November), Kosai sees average daytime highs around 23°C and overnight lows near 16°C, with 559 mm of rain over about 35 wet days across the season. It is the 2nd-warmest season and the 2nd-wettest season.
Over the season highs ease from about 30°C in early September to 15°C by late November. The sky is clear or mostly clear about 40% of the time across fall, and the air most often feels dry.
Fall is Kosai's best season of the year to visit on our travel score. For the whole year in context, see Kosai's year-round climate.
- Avg daytime high
- 23°C
- 2nd-warmest season
- Avg overnight low
- 16°C
- Rainfall
- 559 mm
- 35 wet days
- Avg wind
- 12 km/h
- Travel score
- 5.9
- best season of the year
- Months
- Sep · Oct · Nov
Temperature in Kosai in Fall
Over the season highs ease from about 30°C in early September to 15°C by late November.
A typical fall day in Kosai reaches about 23°C and drops to 16°C overnight. The warmest of the three months is September, the coolest November.
How fall really feels in Kosai
Once humidity and wind are folded in, fall brings about 6 days that feel above 32°C and 0 that feel at or below 0°C.
The story in fall is heat — humidity pushes the afternoon "feels like" well above the raw temperature.
Kosai weather by month
How the three fall months (September, October and November) 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 Fall
The sky is clear or mostly clear about 40% of the time across fall.
Chance of precipitation in Fall
Kosai gets around 559 mm of rain over 35 wet days across fall. The line is the day-by-day chance of measurable precipitation.
Humidity in Fall
Most of fall feels dry — the stacked bands show each day's mix of comfort levels, read off the dew point.
Wind in Fall
Winds average 12 km/h across fall.
Sunrise & sunset in Fall
Daylight runs from about 12 h 48 min in early September to 9 h 54 min by late November. The lit band spans sunrise to sunset each day.
Solar energy in Fall
Average shortwave solar energy reaching the ground each day across fall, about 3.4 kWh/m².
Hazard calendar for Kosai
In fall, 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 fall a good time to visit Kosai?
Our two travel scores rate fall for general sightseeing and for beach or pool weather — 0 (poor) to 10 (ideal), averaged across the three months.
fall is a reasonable time to visit Kosai for sightseeing.
What to pack for Kosai in Fall
From fall's temperature range, rain chance, sun and wind — what's worth putting in the bag.
In fall, Kosai sees daytime highs around 23°C and nights near 16°C. Pack light clothes and rain gear. About 35 days see rain.
Sea temperature near Kosai in Fall
The nearest coast averages about 23°C across fall — 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 Fall
Clear-sky midday UV across fall averages around 6 — 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 Fall
Average fine-particle pollution (PM2.5) through the year — so you can see where fall 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.