Climate Overview
The climate in Isumi is warm and mild. The average annual temperature is 18°C and approximately 2066mm of precipitation falls per year. Isumi receives a notable amount of rainfall throughout the year, including during its driest month. Isumi is in the Northern Hemisphere. Summer begins at the end of June and lasts through September. The summer months are: August, September, July. The coldest months are February, January, March, when temperatures can drop to 8°C.
Temperature
Isumi sees moderate temperature variation throughout the year, ranging from 8°C to 28°C. The warmest month is August, when average highs reach 28°C and the mean temperature sits around 27°C. February is the coolest month, with minimum temperatures around 8°C and an average of 10°C. Daily temperature variation is modest, with an average difference of 3°C between highs and lows. The sharpest temperature change occurs between November and December, with a 4°C shift in average temperatures.
Precipitation
Isumi is a very wet location, receiving approximately 2066mm of precipitation annually, which averages out to around 172mm per month. The wettest month is September, averaging 263mm of rainfall. October and June also tend to see above-average precipitation. The driest month is February, with just 110mm. That's 153mm less than September, the wettest month. Rainfall is relatively evenly distributed throughout the year, so there is no pronounced dry or wet season to plan around.
Wind
Isumi is relatively calm, with an average annual wind speed of 7km/h. For context, sustained winds below 12km/h are generally light, while anything above 25km/h is considered strong. The windiest month is January, averaging 7km/h, though still comfortable for most outdoor activities. The calmest conditions occur in June, with average winds dropping to 6km/h, making it an ideal period for wind-sensitive activities. Wind conditions are fairly consistent throughout the year, varying by only 1km/h between the calmest and windiest months.
Seasons
92 days until Autumn
It is currently summer in Isumi, which began on June 21, 2026. Isumi is in the Northern Hemisphere, where spring begins in March, summer in June, autumn in September, and winter in December. The warmest period peaks in August at around 28°C, while the coldest stretch bottoms out in February near 8°C. Autumn is next, beginning on September 23, 2026 — 92 days from now.
Spring
Temperatures range from 11 to 20°C. Rainfall is heavy, totalling around 468mm across the season with a monthly average of 156mm. Winds are generally light, averaging 7km/h. An umbrella or waterproof jacket is advisable as spring showers are frequent.
Summer
Temperatures range from 21 to 28°C. Rainfall is heavy, totalling around 528mm across the season with a monthly average of 176mm. Winds are generally light, averaging 6km/h. Light, breathable clothing is ideal — perfect conditions for outdoor activities.
Autumn
Temperatures range from 15 to 26°C. Rainfall is heavy, totalling around 710mm across the season with a monthly average of 237mm. Winds are generally light, averaging 7km/h. A waterproof jacket and sturdy footwear are recommended as rain becomes more frequent.
Winter
Temperatures range from 8 to 14°C. Rainfall is heavy, totalling around 361mm across the season with a monthly average of 120mm. Winds are generally light, averaging 7km/h. A light jacket or sweater is usually sufficient, though cooler evenings may call for an extra layer.
Monthly Climate Data
The table below shows monthly climate averages for Isumi based on historical weather data. Min and max temperatures represent typical overnight lows and afternoon highs for each month, shown in degrees Celsius (°C). Precipitation is measured in millimetres (mm) and indicates the average total rainfall per month. Wind speed is the average sustained speed in kilometres per hour (km/h). All values are based on averages from over 10 years of historical weather data. The current month is highlighted for quick reference.
