Kosai has a warm temperate climate with warm summers and mild winters.
Temperatures peak in August and drop to their lowest in January, while rainfall is highest during summer months.
Humidity remains high throughout the year creating warm and humid conditions.
| Month | 🌤️ | High | Low | Avg | Humid % | Rain (mm) | Wind (m/s) | Solar (kWh/m²) |
|---|---|---|---|---|---|---|---|---|
| January | 🌨️ | 16.3°C | 3.4°C | 9.8°C | 75% | 61 | 7.4 | 2.72 |
| February | 🌤️ | 16.5°C | 3.6°C | 10.1°C | 73% | 78 | 7.1 | 3.41 |
| March | ☔ | 18.1°C | 5.2°C | 11.7°C | 73% | 146 | 6.5 | 4.17 |
| April | 🌧️ | 20.6°C | 8.4°C | 14.5°C | 75% | 178 | 5.6 | 4.93 |
| May | 🌧️ | 23.5°C | 13.5°C | 18.5°C | 80% | 204 | 4.8 | 5.22 |
| June | 🌧️ | 26.5°C | 18.0°C | 22.3°C | 85% | 250 | 4.3 | 4.84 |
| July | 🌧️ | 29.4°C | 22.1°C | 25.8°C | 88% | 225 | 4.0 | 5.36 |
| August | 🌧️ | 30.5°C | 24.1°C | 27.3°C | 85% | 181 | 4.2 | 5.55 |
| September | 🌧️ | 29.1°C | 20.5°C | 24.8°C | 80% | 244 | 4.8 | 4.25 |
| October | 🌧️ | 25.9°C | 14.9°C | 20.4°C | 74% | 194 | 5.4 | 3.33 |
| November | ☔ | 22.2°C | 10.0°C | 16.1°C | 73% | 106 | 5.9 | 2.77 |
| December | 🌤️ | 18.7°C | 5.5°C | 12.1°C | 74% | 60 | 6.9 | 2.50 |
Showing average climate conditions across 45 years (1981–2025)
🧥 Light layers are sufficient — this Mild Winter stays cool without prolonged hard freezes.
🌤️ Early mornings and evenings are most comfortable during this Hot Summer season.
☔ Heavy Rainfall expected — carry rain gear and plan outdoor activities around these months.
Monthly averages · 1981–2025 climate normals · °C
Temperatures rise steadily from spring, peak in August, and gradually decline through autumn into winter.
These seasonal patterns offer comfortable conditions year-round, with warm summers and mild winters.
Monthly rainfall · 1981–2025 seasonal trends · mm/month
Rainfall is concentrated in the summer months. Humidity stays high (around 78%), peaking during summer months, which creates warm and humid conditions.
☔ Heavy Rainfall expected — carry rain gear and plan outdoor activities around these months.
Monthly averages · 1981–2025
Across 45 years of records, Kosai's temperature shows a slight warming trend over the past decade. Its hottest day reached 33.1°C in August 2024, and its coldest dropped to -0.5°C in February 1981. 2024 was the warmest year overall and 1986 the coolest.
The warmest year in Kosai's recorded history was 2024 (avg: 19.4°C), while the coldest was 1986 (avg: 16.8°C).
Average annual high/low · Last 30 years · °C
Total annual precipitation · Last 30 years · mm/year
| Year | Min Temp | Avg Temp | Max Temp | Rainfall (mm) | Avg Humidity | Avg Wind |
|---|---|---|---|---|---|---|
2025 | 13.8°C | 18.6°C | 23.4°C | 2245 | 79% | 5.4 m/s |
2024 🔥 🌧️ | 14.4°C | 19.4°C | 24.5°C | 3223 | 79% | 5.4 m/s |
2023 | 13.5°C | 18.7°C | 24.0°C | 2939 | 77% | 5.2 m/s |
2022 | 13.7°C | 18.5°C | 23.2°C | 2534 | 78% | 5.4 m/s |
2021 | 13.1°C | 18.4°C | 23.7°C | 2834 | 77% | 5.6 m/s |
2020 | 14.0°C | 18.8°C | 23.6°C | 2473 | 77% | 5.5 m/s |
2019 | 13.8°C | 18.7°C | 23.6°C | 2152 | 77% | 5.6 m/s |
2018 | 13.2°C | 18.4°C | 23.5°C | 2481 | 78% | 5.5 m/s |
2017 | 12.6°C | 17.6°C | 22.6°C | 1865 | 77% | 5.5 m/s |
2016 | 13.1°C | 18.3°C | 23.5°C | 2495 | 78% | 5.2 m/s |
Showing 1 to 10 of 45 years
Based on 45 years of data (1981–2025), August is typically the hottest month in Kosai, Shizuoka, with average high temperatures around 30.5°C.
January is the coldest month in Kosai, with average low temperatures around 3.4°C.
June receives the most rainfall with approximately 250 mm, while December is the driest with 60 mm.
The highest recorded temperature was 33.1°C in August 2024. This is part of the historical record spanning 1981–2025.
The lowest recorded temperature was -0.5°C in February 1981.
This page covers 45 years of climate data from 1981 to 2025. As new data is added to the database the page automatically reflects the updated coverage.
Kosai receives the most sunlight in August with an average solar radiation of 5.55 kWh/m²/day. This solar radiation data, sourced from NASA POWER, is useful for solar energy planning and agriculture in Shizuoka.
All climate data is sourced from NASA POWER (Prediction Of Worldwide Energy Resources), based on MERRA-2 satellite and model data. It provides monthly averages for temperature, precipitation, humidity, wind speed, and solar radiation.
All weather data is sourced from NASA POWER (Prediction of Worldwide Energy Resources), a NASA project providing solar and meteorological data for renewable energy, building efficiency, and agricultural research.
