Iwanuma climate — normals and trends
Iwanuma (Japan) has a humid subtropical climate (Cfa) under the Köppen-Geiger classification. Its mean annual temperature is 11.5 °C and it receives 1,328 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 (23.5 °C on average) and the coldest is January (0.3 °C). Rainfall peaks in September.
Iwanuma averages 77 frost days, 5 hot days (≥ 30 °C) and 148 rainy days per year.
Iwanuma has warmed by +2.4 °C between 1940 and 2025, or +0.28 °C per decade. This trend is statistically significant.
The number of frost days there went from about 100 to 54 per year over the period.
The hottest day of the period reached 34.0 °C (on 15 August 1994) and the coldest -14.7 °C (on 17 January 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
IwanumaMiyagi
- coords
- 38.10°, 140.86°
- period
- 1940–2025 · 86 yrs
Mean daily temperature
11.5°C
Average daily high
14.8°C
Average daily low
8.3°C
Annual rainfall
1,328mm
Sunshine / day
8.3h
Mean relative humidity
76%
Average peak wind
16.4km/h
Seasonal range
23.2°C
Frost days (< 0 °C)
77 d/yr
Hot days (≥ 30 °C)
5 d/yr
Rainy days (≥ 1 mm)
148 d/yr
Annual snowfall
69.0 cm
Average feels-like high
13.6 °C
Average feels-like low
6.5 °C
Average peak gust
36.3 km/h
Tropical nights (≥ 20 °C)
44 d/yr
Solar radiation
13.5 MJ/m²
Has the climate changed?
One stripe per year, 1940 to 2025
+2.4 °C
since 1940
+0.3 °C per decade · r² = 0.59 · 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
34.0 °C
15 August 1994
Coldest day
-14.7 °C
17 January 1942
Wettest day
190 mm
12 October 2019
Windiest day
57.4 km/h
31 January 1970
Strongest gust
142.9 km/h
27 September 1959
Hottest feels-like
40.2 °C
30 July 2023
Coldest feels-like
-19.8 °C
9 February 1942
Snowiest day
41.4 cm
24 December 1980
Sunniest day
14.3 h
19 June 2007
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 | 5.5 °C | +1.8 °C | 47 mm | -5 mm |
| Feb | 4.7 °C | +0.4 °C | 32 mm | -23 mm |
| Mar | 10.2 °C | +2.4 °C | 90 mm | +7 mm |
| Apr | 14.4 °C | +0.9 °C | 117 mm | +23 mm |
| May | 18.5 °C | +0.6 °C | 200 mm | +94 mm |
| Jun | 24.9 °C | +4.3 °C | 94 mm | -49 mm |
| Jul | 28.9 °C | +4.5 °C | 91 mm | -94 mm |
| Aug | 29.1 °C | +2.8 °C | 184 mm | +19 mm |
| Sep | 25.8 °C | +2.9 °C | 170 mm | -17 mm |
| Oct | 18.3 °C | +0.7 °C | 181 mm | +44 mm |
| Nov | 13.3 °C | +1.2 °C | 50 mm | -18 mm |
| Dec | 8.3 °C | +1.7 °C | 70 mm | +16 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 Iwanuma?
Iwanuma has a humid subtropical climate (Köppen Cfa). Over 1940-2025, the average annual temperature is 11.5 °C and it receives 1,328 mm of precipitation per year.
What is the hottest day ever recorded in Iwanuma?
The hottest day measured in Iwanuma between 1940 and 2025 was 15 August 1994, reaching 34.0 °C.
What is the coldest day in Iwanuma?
The coldest day measured in Iwanuma between 1940 and 2025 was 17 January 1942, at -14.7 °C.
Does it snow in Iwanuma?
Yes. Iwanuma gets on average 69.0 cm of snow per year and has around 77 frost days.
Has the climate of Iwanuma warmed?
Yes: Iwanuma warmed by +2.4 °C between 1940 and 2025, a statistically significant trend.
What is the wettest day in Iwanuma?
The wettest day measured in Iwanuma between 1940 and 2025 was 12 October 2019, with 190 mm of rain in 24 hours.
What was the windiest day in Iwanuma?
The windiest day measured in Iwanuma between 1940 and 2025 was 31 January 1970, with winds reaching 57.4 km/h.
What is the warmest month in Iwanuma?
The warmest month in Iwanuma is August (23.5 °C on average); the coldest is January (0.3 °C).
How much does it rain in Iwanuma?
Iwanuma receives on average 1,328 mm of precipitation per year, spread over about 148 rainy days.
Is it sunny in Iwanuma?
Iwanuma gets on average 8.3 hours of sunshine per day, roughly 3,030 hours per year over 1940-2025.
What is the biggest single-day snowfall in Iwanuma?
The heaviest 24-hour snowfall measured in Iwanuma between 1940 and 2025 was 24 December 1980, with 41.4 cm.
Are there tropical nights in Iwanuma?
Yes: Iwanuma has on average 44 tropical nights per year (temperature staying above 20 °C), over 1940-2025.
What was the most extreme apparent temperature in Iwanuma?
In Iwanuma, between 1940 and 2025, the highest apparent temperature reached 40.2 °C on 30 July 2023, and the lowest was -19.8 °C on 9 February 1942.
Compare Iwanuma with another city
Pick a second city: its normals will be set against these, indicator by indicator.
Nearby cities
The climate around Iwanuma