The climate of Hiroshima, a Japanese city in the southwestern part of Honshu Island, is temperate humid, with quite mild winters and muggy, rainy summers. Like the rest of Japan, the city is affected by the monsoon circulation: in winter, the northwest cold currents prevail, while in summer, they are replaced by hot and humid currents of tropical origin.
The town is located on the coast, in the Seto Inland Sea, a short distance from Shikoku and Kyushu islands.
In winter, there are fairly mild periods, with highs above 10 °C (50 °F), alternating with cold periods, with wind and rain, highs around 5/7 °C (41/45 °F) or less, and possible falls of sleet or snow. Snowfalls, however, are generally light, as are nocturnal frosts.
Summers are hot and humid; there can be periods of good weather, with maximum temperatures around 35 °C (95 °F), tropical nights and high humidity, but also periods of bad weather due to the summer monsoon. August is the hottest month, both because of the thermal inertia of the sea and because of the lower frequency of periods of bad weather. Here are the average temperatures.
Hiroshima - Average temperatures
Min (°C)2251015192425211484
Max (°C)101114202427313229231712
Min (°F)363641505966757770574639
Max (°F)505257687581889084736354

It should be noted that the temperatures recorded at the airport, which is located in a green zone, about 40 kilometers (25 miles) east of the city, and 330 meters (1,080 feet) above sea level, are much lower than those recorded in the city: for example, in January 2016, the temperature dropped to -8 °C (18 °F) at the airport and to -4 °C (25 °F) in the city.
Rainfall is abundant, in fact, it amounts to 1,500 millimeters (60 inches) per year. Winter is undoubtedly the driest season, at least in quantity. The rainiest months are June and July, ie the first period of the rainy season (called Baiu). In August, there is a certain decrease in rain frequency: on average, among the summer months, it is the hottest as well as the driest and sunniest. Here is the average precipitation.
Hiroshima - Average precipitation

From June to October (but especially from August to early October), Hiroshima can be affected by typhoons, the tropical cyclones of Southeast Asia, though this area, in the Seto Inland Sea, is relatively protected (however, in September 1945, the city was hit by a typhoon that caused a lot of damage).
The cherry blossoming in Hiroshima occurs around April 2-3.
The amount of sunshine in Hiroshima is not very good, however, there are two relative maxima, one in spring (April-May) and the other in August, after the Baiu rains, both with 6.5/7 hours of sunshine per day. Here are the average sunshine hours per day.
Hiroshima - Sunshine


The sea in Hiroshima is warm enough for swimming, with a temperature of 23 °C (73 °F) or more, from July to October, and it becomes pleasantly warm in August.
Hiroshima - Sea temperature
Temp (°C)161515161922252726232118
Temp (°F)615959616672778179737064