Seirō, Japan experiences average highs of 17°C (63°F) and lows of 10°C (50°F) throughout the year. Rainfall is frequent, averaging about 19 rainy days per month. Average highs have stayed broadly stable across the available records.
Seirō, Japan Weather & Climate 2026
Monthly climate averages for Seirō, Japan. Based on 10-year ERA5 reanalysis data.
Climate Overview
Drier season: Mar–Oct 
Wetter season: Jan–Dec At-a-Glance Climate Summary
Live Weather & Air Quality
Key figures
Climate Score
4.6/10
Best: May, June, September, October
UV Index
5
Low
Temperature 17°C / 10°C
Feels Like 17°C / 9°C
Rainy Days 19
Rainfall 191 mm
Sunshine 8 h
Humidity 80%
Wind Speed 17 km/h
Dew Point 10°C
Snow Days 12 days
Frost Days 12 days
Hottest Month
30°C
August
Avg Low 23°C
Rain 18 days
Coldest Month
-1°C
January
Avg High 4°C
Rain 27 days
Driest Month
14 days
May
Avg High 21°C
Avg Low 12°C
Windiest Month
22 km/h
January (Gusts 46)
Sea Temperature
10°C – 29°C
Warmest water: August (
29.3°C
)
Worst Time to Visit
Consider avoiding January, February, March, December due to very cold temperatures, heavy rainfall.
Sun Position
Sunrise 04:20
Daylight 14.8h
Sunset 19:07
Live conditions —
Seirō on the map · live conditions
Seirō, Japan
- Continent
- Asia
- Country
- Japan
- City
- Seirō
- Population
- 14.3K
- Coordinates
- 37.98°, 139.25°
Seasonal Breakdown
Spring
Mar–May
Avg High 15°C
Avg Low 7°C
Rain 16 days/mo
1/3 best months
Summer
Jun–Aug
Avg High 27°C
Avg Low 21°C
Rain 17 days/mo
1/3 best months
Autumn
Sep–Nov
Avg High 19°C
Avg Low 13°C
Rain 17 days/mo
2/3 best months
Winter
Dec–Feb
Avg High 5°C
Avg Low 0°C
Rain 25 days/mo
Climate Charts
Based on historical averages (2016–2025)
Monthly Temperatures
High Low Shaded bands show the typical range across the available yearly records.
Line chart showing monthly temperatures. Jan: 4°C / -1°C . Feb: 4°C / -1°C . Mar: 10°C / 2°C . Apr: 16°C / 7°C . May: 21°C / 12°C . Jun: 24°C / 17°C . Jul: 28°C / 22°C . Aug: 30°C / 23°C . Sep: 26°C / 19°C . Oct: 19°C / 13°C . Nov: 13°C / 7°C . Dec: 7°C / 2°C .
Monthly Rainfall
Rainfall
Bar chart showing monthly rainfall. Jan: 237 mm. Feb: 161 mm. Mar: 136 mm. Apr: 132 mm. May: 134 mm. Jun: 160 mm. Jul: 256 mm. Aug: 238 mm. Sep: 193 mm. Oct: 171 mm. Nov: 191 mm. Dec: 277 mm.
Monthly Humidity
Humidity
Line chart showing monthly humidity. Jan: 82%. Feb: 79%. Mar: 76%. Apr: 76%. May: 77%. Jun: 82%. Jul: 84%. Aug: 83%. Sep: 82%. Oct: 80%. Nov: 79%. Dec: 83%.
Monthly Wind Speed
Wind Speed Gusts
Bar chart showing monthly wind speed. Jan: 22 km/h . Feb: 21 km/h . Mar: 19 km/h . Apr: 18 km/h . May: 16 km/h . Jun: 14 km/h . Jul: 13 km/h . Aug: 14 km/h . Sep: 15 km/h . Oct: 17 km/h . Nov: 19 km/h . Dec: 22 km/h .
Sunshine
Sunshine
Sunshine: Jan: 6h. Feb: 7h. Mar: 8h. Apr: 9h. May: 10h. Jun: 10h. Jul: 10h. Aug: 10h. Sep: 8h. Oct: 7h. Nov: 7h. Dec: 6h.
Sea Temperature
Sea Temperature swim
Line chart showing monthly sea temperature. Jan: 11°C . Feb: 10°C . Mar: 10°C . Apr: 12°C . May: 16°C . Jun: 21°C . Jul: 26°C . Aug: 29°C . Sep: 28°C . Oct: 23°C . Nov: 18°C . Dec: 14°C .
UV Index
UV Index
Bar chart showing monthly UV index. Jan: UV 3. Feb: UV 4. Mar: UV 5. Apr: UV 6. May: UV 6. Jun: UV 7. Jul: UV 7. Aug: UV 7. Sep: UV 6. Oct: UV 4. Nov: UV 3. Dec: UV 2.
Monthly Daylight Hours
Daylight 12h reference
Monthly Dew Point & Comfort
Dew Point Dry Comfortable Humid Muggy Oppressive
Snow Days
Snow Days Snowfall
Snow Days: Jan: 23 days. Feb: 19 days. Mar: 10 days. Apr: 1 days. May: 0 days. Jun: 0 days. Jul: 0 days. Aug: 0 days. Sep: 0 days. Oct: 0 days. Nov: 2 days. Dec: 16 days.
Climate Trends
Average highs have stayed broadly stable across the available records. Average rainfall is trending wetter by about 49 mm.
2016 to 2025
Avg high Avg rainfall
Climate summary
| Last 12 months | All years | |
|---|---|---|
| Hottest month | Jul 2025 · 32°C | Aug · 30°C |
| Coldest month | Feb 2025 · -1°C | Jan · -1°C |
| Wettest month | Aug 2025 · 342 mm | Dec · 277 mm |
| Windiest month | Feb 2025 · 23 km/h | Jan · 22 km/h |
Month-by-Month Weather Table
January
Wet 
February
Wet March
Wet April
Fair May best
Excellent June best
Excellent July
Wet August
Wet September best
Excellent October best
Good November
Wet December
Wet | Month | Temp | Feels Like | Rain | Sun | Humidity | UV | Status | Details |
|---|---|---|---|---|---|---|---|---|
| January | 4°C / -1°C | -1°C / -6°C | 27days (237 mm) Wet | 5.8h Fair | 82% Humid | 2.5 Moderate | Wet | View Details |
| February | 4°C / -1°C | 0°C / -6°C | 22days (161 mm) Wet | 7.4h Good | 79% Humid | 3.5 Moderate | Wet | View Details |
| March | 10°C / 2°C | 7°C / -2°C | 18days (136 mm) Wet | 8.1h Good | 76% Humid | 4.6 Moderate | Wet | View Details |
| April | 16°C / 7°C | 14°C / 4°C | 15days (132 mm) Wet | 9.2h Good | 76% Humid | 5.7 High | Fair | View Details |
| May best | 21°C / 12°C | 22°C / 11°C | 14days (134 mm) Wet | 9.5h Good | 77% Humid | 5.7 High | Excellent | View Details |
| June best | 24°C / 17°C | 27°C / 18°C | 15days (160 mm) Wet | 9.6h Good | 82% Humid | 6.6 High | Excellent | View Details |
| July | 28°C / 22°C | 33°C / 25°C | 18days (256 mm) Wet | 9.5h Good | 84% Humid | 6.9 High | Wet | View Details |
| August | 30°C / 23°C | 35°C / 27°C | 18days (238 mm) Wet | 9.9h Good | 83% Humid | 7 High | Wet | View Details |
| September best | 26°C / 19°C | 29°C / 21°C | 16days (193 mm) Wet | 8.1h Good | 82% Humid | 5.6 High | Excellent | View Details |
| October best | 19°C / 13°C | 19°C / 11°C | 15days (171 mm) Wet | 7.1h Good | 80% Humid | 4 Moderate | Good | View Details |
| November | 13°C / 7°C | 11°C / 4°C | 20days (191 mm) Wet | 6.8h Fair | 79% Humid | 2.8 Moderate | Wet | View Details |
| December | 7°C / 2°C | 3°C / -3°C | 27days (277 mm) Wet | 5.6h Fair | 83% Humid | 1.8 Low | Wet | View Details |
Compare Nearby City Climates
Frequently Asked Questions
The best months to visit Seirō are May, June, September, October, when temperatures are comfortable and rainfall is at its lowest. This is based on 10-year climate averages for Seirō, scoring temperature, rainfall, humidity, and sunshine hours.
The hottest month in Seirō is August, with average daytime highs of 30°C (85°F). Plan outdoor activities for early morning or late afternoon if visiting during this period.
The coldest month in Seirō is January, with average overnight lows of -1°C (30°F). Pack warm layers and expect shorter daylight hours during this period.
The wettest month in Seirō is December, averaging 277mm of precipitation across 27 rainy days. An umbrella or waterproof jacket is essential.
The rainy season in Seirō runs through January, December, February, November, with the heaviest rainfall in January. Based on 10-year averages for Seirō.
Seirō receives approximately 97 sunshine hours per year. The sunniest month is August with around 10 hours. Based on climate data for Seirō.
The least favorable months to visit Seirō are January, February, March, December, primarily due to very cold temperatures, heavy rainfall. For the best conditions, consider May, June, September, October instead.
The annual average UV index in Seirō is 5, classified as moderate. Standard sun protection (sunscreen, hat) is recommended during prolonged outdoor exposure.
Average humidity in Seirō is 80%, classified as humid. Humidity levels are generally comfortable and should not affect outdoor activities for most people.
Yes — sea temperatures in July, August, September, October average 27°C (81°F), which is warm and comfortable for swimming and water activities.
Yes, Seirō receives snow. Months with snowfall average 12 snow days and 34 cm (13 in) of accumulation, with about 12 frost days during winter.
Average wind speeds in Seirō are 17 km/h (11 mph). The windiest month is January with peak winds reaching 22 km/h (13 mph) (gusts up to 46 km/h / 28 mph).
Seirō averages 2 clear-sky days per month with overall cloud cover around 69%. The clearest skies occur in May.
The annual average dew point in Seirō is 10°C (50°F), which feels pleasant with low humidity. Outdoor activities are comfortable year-round from a humidity standpoint.
Seirō has a Humid Subtropical climate, classified as Cfa under the Köppen system. Temperate climates have mild winters and warm summers, with rainfall spread across the year and four distinct seasons.
The 'feels like' temperature in Seirō ranges from 9°C (48°F) to 17°C (63°F) on average. The 'feels like' temperature closely matches the actual temperature throughout most of the year.
Yes, June is a great time to visit Seirō. It earns a climate score of 7.7/10 with Excellent.
For June in Seirō, pack Umbrella, Waterproof jacket, Waterproof shoes, Breathable clothing, Sunscreen (SPF 30+). With average highs of 24°C (76°F) and 15 rainy days, these essentials will keep you comfortable.
Data Source
Climate data derived from ERA5 reanalysis (ECMWF), averaged over 2016–2025. Sea surface temperature from marine reanalysis data. Climate scores and seasonal estimates are computed by WorldStats.
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