Isumi in Fall
In fall (September, October and November), Isumi sees average daytime highs around 21°C and overnight lows near 19°C, with 575 mm of rain over about 43 wet days across the season. It is the 2nd-warmest season and the wettest season of the year.
Over the season highs ease from about 27°C in early September to 16°C by late November. The sky is clear or mostly clear about 31% of the time across fall, and the air most often feels dry.
Fall is Isumi's 2nd-best season to visit on our travel score. For the whole year in context, see Isumi's year-round climate.
- Avg daytime high
- 21°C
- 2nd-warmest season
- Avg overnight low
- 19°C
- Rainfall
- 575 mm
- 43 wet days
- Avg wind
- 18 km/h
- Travel score
- 5.6
- 2nd-best season
- Months
- Sep · Oct · Nov
Temperature in Isumi in Fall
Over the season highs ease from about 27°C in early September to 16°C by late November.
A typical fall day in Isumi reaches about 21°C and drops to 19°C overnight. The warmest of the three months is September, the coolest November.
Isumi 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° / 7° | 108 | 10.7 | 9.9 | 2.5 |
| Feb | 11° / 6° | 101 | 10.6 | 10.7 | 2.4 |
| Mar | 13° / 9° | 159 | 14.6 | 11.7 | 3.2 |
| Apr | 16° / 13° | 126 | 12.6 | 12.9 | 4.8 |
| May | 20° / 17° | 138 | 11.8 | 13.8 | 5.9 |
| Jun | 23° / 20° | 190 | 13.5 | 14.3 | 5.8 |
| Jul | 26° / 24° | 133 | 11.8 | 14.1 | 6.2 |
| Aug | 28° / 25° | 100 | 11 | 13.3 | 6.2 |
| Sep | 25° / 23° | 188 | 14.7 | 12.2 | 5.9 |
| Oct | 21° / 19° | 239 | 14.9 | 11.1 | 5.8 |
| Nov | 17° / 14° | 147 | 13.4 | 10.1 | 5.2 |
| Dec | 13° / 9° | 106 | 11.7 | 9.7 | 3.6 |
Cloud cover in Fall
The sky is clear or mostly clear about 31% of the time across fall.
Chance of precipitation in Fall
Isumi gets around 575 mm of rain over 43 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 18 km/h across fall.
Sunrise & sunset in Fall
Daylight runs from about 12 h 48 min in early September to 9 h 48 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 3.2 kWh/m².
Hazard calendar for Isumi
In fall, Isumi overlaps its pacific typhoon season. The full year is below, with each hazard's peak months called out.
Isumi sits in the Pacific typhoon belt; the season peaks July–October.
Is fall a good time to visit Isumi?
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 Isumi for sightseeing.
What to pack for Isumi in Fall
From fall's temperature range, rain chance, sun and wind — what's worth putting in the bag.
In fall, Isumi sees daytime highs around 21°C and nights near 19°C. Pack rain gear. Worth having: light clothes. About 43 days see rain.
Sea temperature near Isumi in Fall
The nearest coast averages about 24°C across fall — the other half of the beach question. The full-year curve and swim-comfort zones are below.
The sea offshore is warmest in August at about 26°C and coldest in February near 16°C.
It's comfortable for a long swim from May 22 to Dec 9 — about 6.6 months when the water holds above 20°C.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Sea temperature (°C) | 18 | 16 | 16 | 18 | 20 | 22 | 24 | 26 | 26 | 24 | 22 | 20 |
| Comfort | Cool | Cool | Cool | Cool | Cool | Refreshing | Refreshing | Warm | Warm | Refreshing | Refreshing | Cool |
| Sea temperature (°C) | Comfort | |
|---|---|---|
| Jan | 18 | Cool |
| Feb | 16 | Cool |
| Mar | 16 | Cool |
| Apr | 18 | Cool |
| May | 20 | Cool |
| Jun | 22 | Refreshing |
| Jul | 24 | Refreshing |
| Aug | 26 | Warm |
| Sep | 26 | Warm |
| Oct | 24 | Refreshing |
| Nov | 22 | Refreshing |
| Dec | 20 | Cool |
UV index in Isumi 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 Isumi peaks around August 11 at about 10 (extreme) — 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) | 3 | 4 | 5 | 7 | 9 | 9 | 10 | 10 | 8 | 6 | 4 | 2 |
| Level | Moderate | Moderate | Moderate | High | Very high | Very high | Extreme | Extreme | 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 | 9 | Very high |
| Jul | 10 | Extreme |
| Aug | 10 | Extreme |
| Sep | 8 | Very high |
| Oct | 6 | High |
| Nov | 4 | Moderate |
| Dec | 2 | Moderate |
Air quality in Isumi 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 Isumi is worst in April — around 22 µg/m³ PM2.5 (moderate), about 1.9× the cleanest month (September, 11 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) | 14 | 17 | 21 | 22 | 21 | 16 | 12 | 11 | 11 | 14 | 14 | 13 |
| Level | Moderate | Moderate | Moderate | Moderate | Moderate | Moderate | Good | Good | Good | Moderate | Moderate | Moderate |
| PM2.5 (µg/m³) | Level | |
|---|---|---|
| Jan | 14 | Moderate |
| Feb | 17 | Moderate |
| Mar | 21 | Moderate |
| Apr | 22 | Moderate |
| May | 21 | Moderate |
| Jun | 16 | Moderate |
| Jul | 12 | Good |
| Aug | 11 | Good |
| Sep | 11 | Good |
| Oct | 14 | Moderate |
| Nov | 14 | Moderate |
| Dec | 13 | Moderate |
Where is Isumi?
Isumi sits at 35.2°N, 140.4°E, 1 m above sea level, in Japan. The nearest listed city is Ōhara, 2.0 km away.
Topography around Isumi
How much the land rises and falls, and what covers it, within 3, 16 and 80 km of Isumi.
Within 3 km, the terrain around Isumi has only modest variations in elevation — a maximum elevation change of 86 m around an average of 12 m above sea level; within 16 km, only modest variations in elevation — a maximum elevation change of 229 m; within 80 km, significant variations in elevation — a maximum elevation change of 396 m.
The land around Isumi is covered by water (59%) and trees (27%) within 3 km, water (62%) and trees (27%) within 16 km, and water (55%) and trees (21%) 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 Isumi (35.23°, 140.4049°, elevation 1 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.