Kosai climate — normals and trends
Kosai (Japan) has a humid subtropical climate (Cfa) under the Köppen-Geiger classification. Its mean annual temperature is 16.0 °C and it receives 1,861 mm of precipitation per year.
These figures are normals computed over 86 complete calendar years, from 1940 to 2025, using ERA5 reanalysis data from the Copernicus programme.
The warmest month is August (27.2 °C on average) and the coldest is January (5.2 °C). Rainfall peaks in June.
Kosai averages 18 frost days, 42 hot days (≥ 30 °C) and 139 rainy days per year.
Kosai has warmed by +2.8 °C between 1940 and 2025, or +0.33 °C per decade. This trend is statistically significant.
The number of frost days there went from about 39 to 0 per year over the period.
The hottest day of the period reached 40.7 °C (on 23 July 2018) and the coldest -5.8 °C (on 14 February 1942).
Data from ERA5 reanalysis (Copernicus Climate Change Service), redistributed under a CC-BY 4.0 licence. Normals are recomputed whenever the archive is updated.
Climate normals · ERA5
KosaiShizuoka
- coords
- 34.70°, 137.52°
- period
- 1940–2025 · 86 yrs
Mean daily temperature
16.0°C
Average daily high
19.9°C
Average daily low
12.4°C
Annual rainfall
1,861mm
Sunshine / day
8.6h
Mean relative humidity
71%
Average peak wind
20.6km/h
Seasonal range
22.0°C
Frost days (< 0 °C)
18 d/yr
Hot days (≥ 30 °C)
42 d/yr
Rainy days (≥ 1 mm)
139 d/yr
Annual snowfall
2.0 cm
Average feels-like high
19.2 °C
Average feels-like low
11.1 °C
Average peak gust
41.1 km/h
Tropical nights (≥ 20 °C)
91 d/yr
Solar radiation
14.7 MJ/m²
Has the climate changed?
One stripe per year, 1940 to 2025
+2.8 °C
since 1940
+0.3 °C per decade · r² = 0.70 · p = < 0.001
Trend fitted by linear regression (ordinary least squares) on annual means. A trend is shown only when it is statistically significant (p < 0.05).
A climograph overlays rainfall (bars) and temperature (line): the standard reading in climatology, where you can see at a glance whether the warm season is also the dry one.
Records for the period
Hottest day
40.7 °C
23 July 2018
Coldest day
-5.8 °C
14 February 1942
Wettest day
197 mm
12 October 2019
Windiest day
94.2 km/h
26 September 1959
Strongest gust
204.1 km/h
26 September 1959
Hottest feels-like
44.0 °C
4 August 2024
Coldest feels-like
-11.0 °C
26 February 1981
Snowiest day
12.9 cm
15 February 1968
Sunniest day
14.0 h
12 June 1940
Normals computed over complete calendar years 1940–2025.
A specific year
Pick a year and see how it compares to normal — warmer, drier or more extreme than usual?
Across the whole year
Month by month
| High | vs. normal | Precipitation | vs. normal | |
|---|---|---|---|---|
| Jan | 10.8 °C | +1.5 °C | 35 mm | -21 mm |
| Feb | 9.9 °C | -0.4 °C | 27 mm | -49 mm |
| Mar | 15.6 °C | +1.9 °C | 125 mm | -4 mm |
| Apr | 20.5 °C | +1.9 °C | 128 mm | -25 mm |
| May | 23.1 °C | +0.4 °C | 273 mm | +92 mm |
| Jun | 28.2 °C | +2.7 °C | 245 mm | -7 mm |
| Jul | 32.2 °C | +2.8 °C | 148 mm | -95 mm |
| Aug | 34.0 °C | +3.1 °C | 109 mm | -76 mm |
| Sep | 30.5 °C | +3.0 °C | 253 mm | +20 mm |
| Oct | 23.4 °C | +1.2 °C | 202 mm | +18 mm |
| Nov | 17.5 °C | +0.3 °C | 33 mm | -75 mm |
| Dec | 13.1 °C | +1.3 °C | 76 mm | +14 mm |
The year's extremes
What was the weather like that day?
Your birthday, a wedding, a memorable trip: discover the actual weather for any date since 1940.
Frequently asked questions
What is the climate of Kosai?
Kosai has a humid subtropical climate (Köppen Cfa). Over 1940-2025, the average annual temperature is 16.0 °C and it receives 1,861 mm of precipitation per year.
What is the hottest day ever recorded in Kosai?
The hottest day measured in Kosai between 1940 and 2025 was 23 July 2018, reaching 40.7 °C.
What is the coldest day in Kosai?
The coldest day measured in Kosai between 1940 and 2025 was 14 February 1942, at -5.8 °C.
Does it snow in Kosai?
Yes. Kosai gets on average 2.0 cm of snow per year and has around 18 frost days.
Has the climate of Kosai warmed?
Yes: Kosai warmed by +2.8 °C between 1940 and 2025, a statistically significant trend.
What is the wettest day in Kosai?
The wettest day measured in Kosai between 1940 and 2025 was 12 October 2019, with 197 mm of rain in 24 hours.
What was the windiest day in Kosai?
The windiest day measured in Kosai between 1940 and 2025 was 26 September 1959, with winds reaching 94.2 km/h.
What is the warmest month in Kosai?
The warmest month in Kosai is August (27.2 °C on average); the coldest is January (5.2 °C).
How much does it rain in Kosai?
Kosai receives on average 1,861 mm of precipitation per year, spread over about 139 rainy days.
Is it sunny in Kosai?
Kosai gets on average 8.6 hours of sunshine per day, roughly 3,139 hours per year over 1940-2025.
What is the biggest single-day snowfall in Kosai?
The heaviest 24-hour snowfall measured in Kosai between 1940 and 2025 was 15 February 1968, with 12.9 cm.
Are there tropical nights in Kosai?
Yes: Kosai has on average 91 tropical nights per year (temperature staying above 20 °C), over 1940-2025.
What was the most extreme apparent temperature in Kosai?
In Kosai, between 1940 and 2025, the highest apparent temperature reached 44.0 °C on 4 August 2024, and the lowest was -11.0 °C on 26 February 1981.
Compare Kosai with another city
Pick a second city: its normals will be set against these, indicator by indicator.
Nearby cities
The climate around Kosai