Isumi, Japan climate
Cfa Humid subtropical
Isumi has a seasonal mild-temperate climate (Humid subtropical, Köppen Cfa). The hottest month is August with an average daily high near 29°C, while the coldest is January averaging around 3°C at night. Around 2002 mm of precipitation falls each year, peaking in October (295 mm) and easing off in December (90 mm).
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Summers
Warm
Highs near 29°C in August.
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Winters
Chilly
Lows near 3°C in January.
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Rain
Very wet
About 2002 mm of rain a year.
Wettest in October
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Sky & trend
Often cloudy
Cloudy skies much of the year.
Temperature & precipitation
Daily high–low temperature range with the monthly average, plus monthly precipitation · 1991–2020 normals · hover a month for the exact figuresHours of sunshine per day
Estimated sunny hours each month — daylight length × clear-sky fraction · 1991–2020 monthly cloud cover (NASA POWER)Isumi climate normals (1991–2020)
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Avg high (°C) | 11 | 11 | 14 | 18 | 21 | 24 | 27 | 29 | 27 | 22 | 18 | 14 |
| Avg temp (°C) | 7 | 7 | 10 | 14 | 18 | 21 | 24 | 26 | 24 | 19 | 14 | 9 |
| Avg low (°C) | 3 | 3 | 6 | 11 | 15 | 18 | 22 | 24 | 21 | 16 | 11 | 6 |
| Precipitation (mm) | 104 | 104 | 180 | 158 | 165 | 222 | 166 | 108 | 246 | 295 | 166 | 90 |
| Jan – Jun | Jan | Feb | Mar | Apr | May | Jun |
|---|---|---|---|---|---|---|
| Avg high (°C) | 11 | 11 | 14 | 18 | 21 | 24 |
| Avg temp (°C) | 7 | 7 | 10 | 14 | 18 | 21 |
| Avg low (°C) | 3 | 3 | 6 | 11 | 15 | 18 |
| Precipitation (mm) | 104 | 104 | 180 | 158 | 165 | 222 |
| Jul – Dec | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|
| Avg high (°C) | 27 | 29 | 27 | 22 | 18 | 14 |
| Avg temp (°C) | 24 | 26 | 24 | 19 | 14 | 9 |
| Avg low (°C) | 22 | 24 | 21 | 16 | 11 | 6 |
| Precipitation (mm) | 166 | 108 | 246 | 295 | 166 | 90 |
Sky & atmosphere
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Cloud cover (%) | 61 | 65 | 70 | 69 | 72 | 81 | 74 | 60 | 71 | 72 | 68 | 62 |
| Relative humidity (%) | 74 | 73 | 74 | 77 | 81 | 86 | 88 | 85 | 83 | 80 | 77 | 75 |
| Wind speed (m/s) | 4.4 | 4.4 | 4.4 | 4.0 | 3.5 | 3.1 | 3.1 | 2.9 | 3.4 | 3.8 | 3.8 | 4.2 |
| Jan – Jun | Jan | Feb | Mar | Apr | May | Jun |
|---|---|---|---|---|---|---|
| Cloud cover (%) | 61 | 65 | 70 | 69 | 72 | 81 |
| Relative humidity (%) | 74 | 73 | 74 | 77 | 81 | 86 |
| Wind speed (m/s) | 4.4 | 4.4 | 4.4 | 4.0 | 3.5 | 3.1 |
| Jul – Dec | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|
| Cloud cover (%) | 74 | 60 | 71 | 72 | 68 | 62 |
| Relative humidity (%) | 88 | 85 | 83 | 80 | 77 | 75 |
| Wind speed (m/s) | 3.1 | 2.9 | 3.4 | 3.8 | 3.8 | 4.2 |
Methodology & sources
Temperature & precipitation — the official 1991–2020 climate normals from the Japan Meteorological Agency, measured at Katsuura, about 12 km from the city centre.
Cloud, humidity, wind & sunshine — modelled estimates from NASA POWER, NASA's satellite-and-reanalysis climatology. This is the standard global source for atmospheric variables, which are not measured at most weather stations.