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 84°F, while the coldest is January averaging around 37°F at night. Around 79 inches of precipitation falls each year, peaking in October (11.6 inches) and easing off in December (3.5 inches).
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Summers
Warm
Highs near 84°F in August.
❄️
Winters
Chilly
Lows near 37°F in January.
🌧️
Rain
Very wet
About 79 in 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 (°F) | 52 | 53 | 57 | 64 | 70 | 75 | 80 | 84 | 80 | 72 | 65 | 56 |
| Avg temp (°F) | 44 | 45 | 50 | 58 | 64 | 69 | 75 | 79 | 74 | 66 | 58 | 49 |
| Avg low (°F) | 37 | 38 | 43 | 51 | 59 | 65 | 71 | 74 | 70 | 60 | 51 | 42 |
| Precipitation (in) | 4.1 | 4.1 | 7.1 | 6.2 | 6.5 | 8.7 | 6.5 | 4.2 | 9.7 | 11.6 | 6.5 | 3.5 |
| Jan – Jun | Jan | Feb | Mar | Apr | May | Jun |
|---|---|---|---|---|---|---|
| Avg high (°F) | 52 | 53 | 57 | 64 | 70 | 75 |
| Avg temp (°F) | 44 | 45 | 50 | 58 | 64 | 69 |
| Avg low (°F) | 37 | 38 | 43 | 51 | 59 | 65 |
| Precipitation (in) | 4.1 | 4.1 | 7.1 | 6.2 | 6.5 | 8.7 |
| Jul – Dec | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|
| Avg high (°F) | 80 | 84 | 80 | 72 | 65 | 56 |
| Avg temp (°F) | 75 | 79 | 74 | 66 | 58 | 49 |
| Avg low (°F) | 71 | 74 | 70 | 60 | 51 | 42 |
| Precipitation (in) | 6.5 | 4.2 | 9.7 | 11.6 | 6.5 | 3.5 |
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 (mph) | 9.9 | 9.7 | 9.8 | 8.9 | 7.8 | 6.9 | 6.8 | 6.5 | 7.6 | 8.5 | 8.6 | 9.4 |
| 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 (mph) | 9.9 | 9.7 | 9.8 | 8.9 | 7.8 | 6.9 |
| 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 (mph) | 6.8 | 6.5 | 7.6 | 8.5 | 8.6 | 9.4 |
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.