Weather in Hiroshima

August is the warmest month (average 25.7°C, high 29.7°C) and January is the coolest (average 2.3°C, low -1.5°C). That 23.4°C swing in monthly averages is the first thing to plan around in Hiroshima.

Rain is wet season runs from March to October, inside an annual total of 1556 mm. The wettest month is July at 260 mm; the driest is January at 63 mm. Hiroshima is in Japan at 34.4°N. The 2001–2020 NASA POWER daily record describes a continental climate with a wide temperature swing. On this site the months that score closest to a 22°C day, lighter rain, and moderate humidity are June, July, and September.

Temperature through the year

Monthly average highs run from 6.2°C in January to 29.7°C in August. Nights follow the same curve: -1.5°C in January and 21.7°C in August.

Mean high across all twelve months is 18.2°C and mean low is 9.0°C. These are 20-year grid averages, so a city station can read a few degrees warmer or cooler.

Rain through the year

The wet season in Hiroshima starts in March and ends in October (March, April, May, June, July, August, September, and October). July is the core of it at 260 mm. January is the other extreme, with 63 mm.

A rainy day here is a day with at least 1 mm in the NASA POWER series. July averages 15 such days; January averages 11.

The calendar in Hiroshima

The year bottoms out in January. Plan for -1.5°C at night and 6.2°C in the afternoon. March is when the wet season typically starts in Hiroshima: highs near 11.8°C, and rainfall jumps to 109 mm (12 rainy days). April brings 125 mm and 11 rainy days; temperatures run from 5.9°C to 17.3°C. May stands apart from the months beside it: 22.0°C / 11.1°C and 146 mm. June: 25.3°C high, 16.2°C low, 211 mm rain, 82% humidity. July is the wettest month — 260 mm and 15 rainy days, with 86% humidity.

Peak heat arrives in August: 29.7°C by day, 21.7°C at night, and 83% humidity. September stands apart from the months beside it: 26.0°C / 17.4°C and 170 mm. October closes the wet season: 113 mm over 10 rainy days, then the calendar dries. November brings 79 mm and 10 rainy days; temperatures run from 5.4°C to 14.7°C. In December, Hiroshima averages 8.6°C by day and 0.4°C at night, with 84 mm of rain.

Best months to visit Hiroshima

The three months with the highest comfort score are June, July, and September: June (20.8°C average, 211 mm, 82% humidity); July (24.7°C average, 260 mm, 86% humidity); September (21.7°C average, 170 mm, 83% humidity). They fall in calendar order. The score rewards averages near 22°C, lower rainfall, and humidity near 60%. It is a climate score, not a festival or price calendar.

If you want the wet season itself — fewer crowds, greener landscape, heavier rain — aim at March–October instead of the score.

How Hiroshima compares inside Japan

Fukuoka is about 207 km away: Hiroshima is 1.1°C cooler than Fukuoka in its hottest month and 344 mm drier over the year than Fukuoka. Fukuoka’s wettest month is July (357 mm) versus July here.

Kobe is about 252 km away: Hiroshima is 1.7°C cooler than Kobe in its hottest month and a similar annual rainfall (1526 mm in Kobe). Kobe’s wettest month is July (204 mm) versus July here.

Osaka is about 281 km away: Hiroshima is 0.5°C cooler than Osaka in its hottest month and 197 mm drier over the year than Osaka. Osaka’s wettest month is September (225 mm) versus July here.