Summer in Hiroshima means hot, humid days and frequent rain showers, all shaped by its spot near the Seto Inland Sea.
You’ll usually see average high temperatures around 30–33°C (86–91°F), and the humidity often makes it feel even warmer. That mix of heat and moisture really defines the season, making the climate feel both lively and, let’s be honest, a bit challenging.
Rainfall takes center stage in summer weather here.
June and July kick off the rainy season, with heavy downpours that start to ease up by August, though the air stays sticky.
Between storms, sunshine breaks through, giving you long daylight hours to explore, but you’ll want to plan around those sudden showers.
The sea adds to the humidity and shapes the breezes rolling through the city.
If you know what to expect—heat, humidity, and bursts of rain—you can still make the most of your time in Hiroshima during summer.
Overview of Hiroshima’s Summer Climate
Hiroshima’s summer weather comes from its humid subtropical climate, its spot along the Seto Inland Sea, and the seasonal monsoon.
You’ll get hot temperatures, high humidity, and frequent rainfall, with conditions shifting as the season moves along.
Climate Classification and Key Features
Hiroshima sits in the humid subtropical climate (Cfa) category in the Köppen system.
This means summers are hot, wet, and humid, while winters stay mild with barely any snow.
In summer, daily highs usually hit 27°C (81°F) to 33°C (91°F).
Nights stay warm, often above 22°C (72°F).
Humidity runs high, especially in July, when relative humidity can reach 70–75%.
Rainfall really stands out.
June and July bring the most precipitation because of the East Asian monsoon.
July alone can see 200–250 mm (8–10 inches) of rain.
Thunderstorms and the occasional typhoon show up, but direct hits are less common than in southern Japan.
This combo of heat, moisture, and rainfall makes the air feel heavier than the actual temperature.
If you’re not used to humid summers, outdoor activities can feel extra tiring during peak conditions.
Geographical Influences on Weather
Hiroshima sits on the southwestern part of Honshu, with the Seto Inland Sea to the south and mountains to the north.
This geography creates some unique weather patterns.
The inland sea helps moderate extreme temperatures.
While summers get hot, the sea keeps nights a bit cooler compared to inland cities.
At the same time, the sea adds moisture to the air, bumping up humidity.
The northern mountains block cold winds in winter, but in summer, they trap warm, moist air over the city.
This can intensify the muggy feeling and stretch out rainy spells.
Because of this setting, Hiroshima gets less snow than northern Japan but sees more summer rainfall than areas farther inland.
The mix of sea influence and topography pretty much explains the city’s seasonal weather quirks.
Seasonal Weather Patterns
Summer in Hiroshima stretches from June through September.
Each month brings its own conditions that shape your experience in the city.
- June: The rainy season kicks off. Rainfall often tops 200 mm. Days stay warm, around 27°C (81°F), and humidity climbs fast.
- July: The hottest and wettest month. Highs reach 30–32°C (86–90°F) with heavy rain and frequent thunderstorms.
- August: Still very hot, averaging 27–29°C (81–84°F), but rainfall drops compared to July. Humidity sticks around.
- September: Temperatures ease to 24–28°C (75–82°F). Rainfall picks up again due to typhoons, though storms are usually short-lived.
This seasonal shift means you’ll deal with both extremes—monsoon rains early on and intense heat in midsummer.
By late summer, things get a bit more comfortable, but tropical storms can still shake up your travel plans.
Typical Summer Temperatures and Humidity
Hiroshima has a humid subtropical climate with hot, wet summers.
You’ll face high temperatures, frequent rainfall, and humidity that makes the air feel warmer than the numbers suggest.
Average Highs and Lows by Month
Summer in Hiroshima runs from June through September.
Temperatures climb after the rainy season in June, peak in August, then slowly cool in September.
- June: Highs around 27°C (81°F), lows near 20°C (68°F)
- July: Highs about 30°C (86°F), lows near 23°C (73°F)
- August: Highs average 32–33°C (90–91°F), lows near 25°C (77°F)
- September: Highs around 28°C (82°F), lows near 21°C (70°F)
August usually feels the hottest, with many days above 30°C.
Nights stay warm, so you rarely get much relief from the heat after sunset.
Humidity Levels and Comfort
Humidity really shapes how you experience summer weather in Hiroshima.
Relative humidity often sits above 70%, with July as the muggiest month.
The combo of high moisture and warm temps makes the air feel heavy and sticky.
Even when the thermometer shows moderate numbers, the dampness can make outdoor activities uncomfortable.
You should also watch for sudden rain showers and the occasional thunderstorm, especially in July.
The rainy season from late June to mid-July adds to the dampness, and humidity lingers through August.
Heat Index and Urban Effects
High humidity pushes the heat index—how hot it actually feels—several degrees above the air temperature.
For example, a day at 32°C (90°F) with high humidity can feel more like 38°C (100°F).
Urban areas in Hiroshima, packed with concrete and pavement, trap heat and keep nighttime temperatures higher.
This “urban heat island” effect means evenings can feel warmer than out in the countryside.
If you’re walking through the city in the afternoon, you might notice limited shade and reflective surfaces that just amplify the heat.
Sticking close to rivers or shaded parks can help you escape the urban warmth.
Rainfall and Precipitation Trends
Hiroshima’s summer weather brings frequent rain and high humidity.
You’ll see steady rainfall from June through early September, shaped by both the rainy season and tropical systems.
Monthly Rainfall Totals
Rainfall in Hiroshima jumps sharply in June, the wettest month of the year.
On average, June gets about 212 mm of rain.
July and August also bring heavy totals, usually between 150–200 mm.
By September, rainfall starts to ease, though it still averages more than 100 mm.
The mix of high temperatures and frequent showers keeps summers feeling damp and muggy.
| Month | Avg. Rainfall (mm) |
|---|---|
| June | ~212 |
| July | ~180 |
| August | ~150–170 |
| Sept | ~110–130 |
These numbers show how summer in Hiroshima stays consistently wet, with no truly dry month in the season.
Rainy Days and Storm Patterns
Even when rainfall totals are high, the number of rainy days can change a bit.
June averages around 17 days with measurable rain, and July and August also see frequent showers.
Rain usually comes in bursts, with short but intense downpours, especially in the afternoons.
You’ll probably notice long stretches of cloudy skies that cut down on sunshine hours.
That’s just how humid subtropical climates work—moisture builds up fast and then dumps down in heavy showers.
Thunderstorms aren’t as common as in tropical regions, but they do pop up in summer.
These storms can cause localized flooding, especially in low-lying parts of the city.
Typhoon Season Impact
Hiroshima sits on the Seto Inland Sea, so it’s less exposed than Japan’s Pacific coast, but typhoons still show up now and then.
The main season runs from August through October, with September as the peak.
A passing typhoon can dump 100 mm or more of rain in a single day.
Strong winds are possible, but the city’s inland spot usually takes the edge off compared to coastal cities.
If you’re traveling, keep in mind that train services and flights might get delayed during typhoon events.
Local authorities give clear warnings, and it’s smart to follow their advice if a storm heads your way.
Sunshine Hours and Daylight Duration
In Hiroshima, daylight length and sunshine hours shift quite a bit through the summer months.
These changes affect how much time you get for outdoor activities and how the weather feels during the day.
Daily Sunlight Averages
On average, you’ll get 6 to 8 hours of direct sunlight per day in summer.
June usually brings about 6 hours, July climbs closer to 7, and August often reaches around 8 hours of sun each day.
Even with long daylight, cloud cover and humidity can cut down the amount of bright sunshine you actually see.
In June, only about 45% of daylight hours end up sunny, while August can hit 60%.
That difference means August feels brighter and a bit drier compared to the early rainy stretch in June.
Here’s a quick look at average sunlight hours per day:
| Month | Avg. Sunlight Hours | % of Daylight Sunny |
|---|---|---|
| June | ~6h 22m | 45% |
| July | ~6h 48m | 48% |
| August | ~8h 00m | 60% |
These averages give you a rough idea of how much usable daylight you’ll have during summer.
Longest and Shortest Summer Days
Day length in Hiroshima changes gradually across summer.
Around the summer solstice in late June, the longest day lasts about 14 hours and 24 minutes.
That’s plenty of daylight for sightseeing, outdoor walks, or evening events.
By August, days shorten a bit to about 13 hours and 24 minutes.
You’ll notice the earlier sunset compared to late June, but days still feel long.
At solar noon in midsummer, the sun climbs high—about 79° above the horizon in June.
This steep angle makes midday hours feel hotter.
From late June to late August, you lose almost an hour of daylight, but there’s still more than enough for full-day activities.
If you’re planning trips that rely on natural light, like hiking or photography, this gradual shift is worth keeping in mind.
Sea Conditions and Seto Inland Sea Influence
The Seto Inland Sea shapes Hiroshima’s summer climate by moderating temperatures and cutting down the impact of strong storms compared to other coastal spots in Japan.
Warm waters, high humidity, and the region’s geography all mix together to affect both the sea and nearby land.
Sea Surface Temperatures
Summer sea temperatures in the Seto Inland Sea climb steadily from June through August.
In early summer, water averages around 70°F (21°C).
By July, it rises to about 78°F (25°C), and in August, it hits 81°F (27°C).
These temps make the sea comfortable for swimming and all sorts of water activities.
The warm seawater also helps keep Hiroshima’s nights mild.
You won’t see sharp drops after sunset because the sea releases stored heat into the air.
This effect adds to the city’s humid nights in July and August.
Since the Seto Inland Sea is semi-enclosed, its waters heat up faster than the open Pacific.
This warming trend stabilizes the local climate, cutting down on extreme swings while still supporting high humidity levels.
If you’re traveling, you can count on consistently warm water if you plan to spend time near the coast.
Coastal Weather Variations
Hiroshima’s geography really shapes the weather, especially when you compare the southern coast to the inland or northern areas. Down by the coast facing the Seto Inland Sea, you’ll usually find warmer, sunnier weather and not much rain.
Head inland or up north, and you’re more likely to get caught in heavier rain or the occasional summer storm.
When typhoons head toward western Japan, they tend to lose some of their punch as they approach the Seto Inland Sea. The islands and the sea’s enclosed shape take the edge off the wind and waves.
Sure, you might still get heavy rain, but the coast doesn’t get hammered as badly as places facing the Pacific.
Humidity sticks around along the coast, but sea breezes often help out in the hottest part of the day. Thanks to those winds and fewer rainy days than up north, the southern coastal strip in Hiroshima feels a bit more inviting for summer outdoor plans.
Travel Tips for Visiting Hiroshima in Summer
Summer in Hiroshima is hot and humid, with plenty of rain showers in June and July. If you plan things out, you can catch cultural events, get outside, and see scenic spots without feeling miserable in the heat.
Best Time to Visit Hiroshima for Summer Activities
The summer season runs from June through August. Early summer, around mid-June to mid-July, brings the rainy season (tsuyu).
Rain falls pretty often during this time, sometimes over 200 mm in a month. Outdoor plans can get washed out, but hydrangea gardens look great and there’s always something to do indoors.
Late July and August crank up the heat. You’ll see highs around 31–33°C (88–91°F) and humidity well over 70%. If you’re into summer festivals or want to check out Miyajima’s beaches, this is the time to go.
For fewer crowds and cooler nights, late August into early September feels more manageable. Typhoons do pop up now and then, so it’s smart to check the weather before you go.
If you’re after cultural events and don’t mind sweating a bit, late July or early August usually hits a good balance.
Recommended Clothing and Precautions
Pack light and go for breathable stuff—think cotton shirts, shorts, or dresses. Sandals or lightweight shoes will keep your feet happy in the heat.
Don’t forget a wide-brimmed hat, sunglasses, and sunscreen. The sun can be pretty relentless.
A folding umbrella or raincoat is a must, since showers can show up out of nowhere. Humidity makes it feel even hotter, so keep water with you and take breaks in the shade or indoors.
If you’re heading out for a hike on Miyajima or want to explore parks, try to start early before it gets too hot. Evenings are more pleasant, but mosquitoes come out, so bring some repellent.
For museums or indoor spots, you’ll be fine with casual, neat clothes—most places have air conditioning, so you can cool off there.
Popular Summer Events and Destinations
Hiroshima puts on a handful of important summer events. Every August 6, people gather at Peace Memorial Park for the Peace Memorial Ceremony.
At night, you’ll see the river glowing during the Toro Nagashi lantern ceremony as thousands of lanterns float downstream.
The Hiroshima Flower Festival happens in early May. It sort of marks the start of the warmer season, even though it’s technically spring.
By mid-summer, you’ll find smaller local festivals and fireworks lighting up the city. On Miyajima Island, folks head to beaches like Tsutsumigaura for swimming or just to unwind.
If you need a break from the heat, try the Hiroshima Peace Memorial Museum or the Mazda Museum—both are indoors and pretty interesting.
For a change of scenery, hop on a ferry to Miyajima in the evening. It’s cooler then, and honestly, the crowds aren’t nearly as intense.