Climate Insights for Isumi

The climate in Isumi is temperate. The average annual temperature is 18°C and approximately 1828mm 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, July, September. The coldest months are January, February, December, when temperatures can drop to 6°C.

Temperatures in Isumi vary considerably across the year, with a 23°C difference between the coldest and warmest months. The warmest month is August, when average highs reach 29°C and the mean temperature sits around 27°C. January is the coolest month, with minimum temperatures around 6°C and an average of 9°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 5°C shift in average temperatures.

Isumi is a fairly wet location, receiving approximately 1828mm of precipitation annually, which averages out to around 152mm per month. The wettest month is September, averaging 221mm of rainfall. June and October also tend to see above-average precipitation. The driest month is January, with just 95mm. That's 126mm 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.

Isumi is moderately windy, with an average annual wind speed of 27km/h. For context, sustained winds below 12km/h are generally light, while anything above 25km/h is considered strong. The windiest month is February, averaging 30km/h, which can feel quite blustery and may affect outdoor activities. The calmest conditions occur in August, with average winds dropping to 23km/h, making it an ideal period for wind-sensitive activities. Wind conditions are fairly consistent throughout the year, varying by only 7km/h between the calmest and windiest months. Wind tends to be stronger during winter months, driven by seasonal pressure systems. The seasonal averages break down to 30km/h in winter, 28km/h in spring, 24km/h in summer, 27km/h in autumn.

It is currently spring in Isumi, which began on March 20, 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 29°C, while the coldest stretch bottoms out in January near 6°C. Summer is next, beginning on June 21, 2026 — 89 days from now.

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.