Japan in summer is hot, humid and, in the big cities, hotter than the thermometer suggests. Tokyo averages a high of 31.3°C (88°F) in August with 30°C reached on 73% of days and nights that stay above 25°C on 47% of nights. Kyoto and Osaka are worse: 35°C on one August day in three in Kyoto, tropical nights on 63% of August nights in Osaka. With humidity around 75%, a 33°C afternoon has a heat index of 40°C, and heatstroke sends tens of thousands of people to hospital every summer.
The national record is 41.1°C, set at Kumagaya (an hour north of Tokyo) in July 2018 and equalled at Hamamatsu in August 2020. This page gives the numbers for 12 cities, explains why Japanese heat feels worse than the same temperature in a dry climate, tells you which places stay comfortable, and lists the coping strategies that locals use and visitors underestimate.
- Hottest month: August (Tokyo 31.3°C high, Osaka and Kyoto 33.7°C)
- Days of 30°C or more in August: Osaka 90%, Kyoto 87%, Fukuoka 79%, Tokyo 73%, Sapporo 16%
- Days of 35°C or more: Kyoto 32% of August days, Osaka 26%, Nagoya 23%, Tokyo 9%
- Tropical nights (low above 25°C): Naha 89%, Osaka 63%, Tokyo 47%, Kyoto 42%, Sapporo 1%
- Coolest big city: Sapporo (26.4°C high, nights 19°C); coolest regions: Hokkaido, the Japan Alps, Nikko, Karuizawa
- National record: 41.1°C (Kumagaya 2018, Hamamatsu 2020)
Check the heat odds for your dates (58 years of records)
Choose a city and date to see how often it reached 30°C and 35°C and how often the night stayed above 25°C on those dates since 1968, plus the actual highs of the last dozen years.
How hot is each city in July and August?
| City | July high / low | August high / low | 30°C+ days (Aug) | 35°C+ days (Aug) | Tropical nights (Aug) | Rain days (Aug) |
|---|---|---|---|---|---|---|
| Sapporo | 25 / 18°C | 26 / 19°C 80°F / 66°F | 16% | 1% | 1% | 30% |
| Sendai | 27 / 20°C | 28 / 22°C 83°F / 71°F | 37% | 2% | 7% | 36% |
| Kanazawa | 30 / 23°C | 31 / 24°C 88°F / 75°F | 69% | 7% | 29% | 30% |
| Tokyo | 30 / 22°C | 31 / 24°C 88°F / 74°F | 73% | 9% | 47% | 27% |
| Chiba (Tokyo Disney Resort) | 29 / 23°C | 31 / 24°C 88°F / 76°F | 68% | 3% | 41% | 25% |
| Nagoya | 31 / 24°C | 33 / 25°C 92°F / 76°F | 84% | 23% | 39% | 28% |
| Kyoto | 32 / 24°C | 34 / 25°C 93°F / 76°F | 87% | 32% | 42% | 29% |
| Osaka | 32 / 25°C | 34 / 26°C 93°F / 78°F | 90% | 26% | 63% | 25% |
| Hiroshima | 31 / 24°C | 33 / 25°C 91°F / 77°F | 81% | 14% | 45% | 24% |
| Fukuoka | 31 / 25°C | 32 / 25°C 90°F / 78°F | 79% | 15% | 54% | 30% |
| Nagasaki | 30 / 24°C | 32 / 25°C 89°F / 78°F | 78% | 6% | 57% | 31% |
| Naha (Okinawa) | 32 / 27°C | 32 / 27°C 89°F / 80°F | 86% | 0% | 89% | 41% |
Three groups emerge. The basin and inland cities (Kyoto, Nagoya, and the towns of the Kanto plain like Kumagaya) reach 35°C most often. The big coastal cities (Osaka, Tokyo, Fukuoka) are slightly less extreme by day but do not cool at night. Hokkaido is a different climate: Sapporo hits 30°C on one day in six and almost never has a tropical night.
Why Japanese heat feels worse than the number
Humidity. Summer air in Tokyo holds 75% relative humidity on an average afternoon, so sweat does not evaporate and the body cannot cool itself. The heat index, the temperature the body actually experiences, is 38°C for a 32°C day at 75% humidity and over 40°C at 34°C. A 35°C day in Kyoto feels like 43°C. Dry-climate visitors from Arizona or Spain are routinely caught out by 31°C days that would be comfortable at home.
Tropical nights. The concrete of a big city stores the day’s heat and releases it after dark, so the temperature in central Osaka or Tokyo often never drops below 26 or 27°C. Nights without relief are what turn a hot week into a dangerous one: sleep suffers, and the body starts the next day already stressed. The night-time figure is the one that separates a coastal city (Naha never reaches 35°C but has tropical nights on 89% of August nights) from a mountain town.
Sun and surfaces. The UV index reaches 8 to 10 in July and August, and asphalt surfaces reach 60°C. The Japanese habit of carrying a parasol, walking on the shaded side of the street and ducking into every air-conditioned building is practical, not fussy.
When is the hottest period, exactly?
The heat builds from the end of the rainy season around 19 July, peaks from late July to about 20 August, and eases after the last week of August. The Obon week (around 13 to 16 August) is usually at or near the peak. A run of 35°C days in Tokyo typically comes with a strong Pacific high and a Tibetan high stacked above it; the 2018 and 2023 summers were the extreme cases, with Tokyo recording more than 20 days above 35°C in 2023. September’s first half remains hot (Tokyo 30°C on 27% of September days), and the real cool-down comes after the equinox.
| Period | Tokyo typical high | What is happening |
|---|---|---|
| 1 to 19 July | 28 to 30°C | End of rainy season; humid, cloudy, first heat warnings |
| 20 July to 10 August | 31 to 34°C | Peak heat begins; fireworks season; heatstroke alerts most days |
| 11 to 20 August | 31 to 34°C | Obon; peak of tropical nights; typhoon risk rising |
| 21 to 31 August | 30 to 32°C | Slight easing; afternoon thunderstorms |
| 1 to 15 September | 28 to 31°C | Late-summer heat; peak typhoon month |
| 16 to 30 September | 25 to 28°C | Relief after the equinox |
Where to escape the heat
- Hokkaido: Sapporo 26°C by day, 19°C at night, dry air; Furano lavender, Biei hills, Shiretoko. See best time to visit Hokkaido.
- The Japan Alps: Kamikochi (1,500m) averages 8°C cooler than Tokyo; Norikura, Hakuba and Tateyama are alpine summer.
- Karuizawa, Nikko and Hakone: the classic Tokyo summer retreats, 4 to 8°C cooler by day and comfortable at night.
- Tohoku: Sendai is 3°C cooler than Tokyo and has the August festivals; Aomori and the Hakkoda mountains are cooler still.
- Okinawa is hot but breezy, rarely above 33°C, and the sea is the coolest place to be; the trade-off is typhoon risk.
- Indoors: Japanese cities are built for it. Underground malls, department store food halls, museums and aquariums are cold enough that a light layer helps.
How to handle the heat: what locals do
- Move early and late. Sightsee from 6 to 10am and after 5pm; temples and gardens open early. Book museums, aquariums and shopping for the middle of the day.
- Drink before you are thirsty, and replace salt: sports drinks (Pocari Sweat, Aquarius) and oral rehydration solution (OS-1) are in every convenience store. Salt tablets and salted candies are sold for the purpose.
- Use the shade tools. A parasol (men use them too now), a wide hat, a cooling towel soaked in water, a folding fan. Cooling sprays and wipes from drugstores work.
- Watch for the warning signs: headache, dizziness, nausea, cramps, no longer sweating. Get into air conditioning, drink, cool the neck and armpits, and call 119 if confusion or collapse occurs. Heatstroke alerts (netsuchusho keikai alert) are issued a day ahead when the heat index will exceed 33.
- Choose the hotel for the night, not the day: strong air conditioning matters more than a view in August, and a room facing away from the afternoon sun is cooler.
- Festivals are worth it (Gion Matsuri, Tenjin Matsuri, the fireworks) if you arrive hydrated, sit in shade, and leave when you start to feel it.
Compare summer in any two cities
The single figure I would check before a summer trip is the number of tropical nights, not the daytime high. A destination where the night drops to 22°C (Sapporo, Karuizawa, Nikko) recovers you for the next day; one where it stays at 27°C (Osaka, Naha, central Tokyo) wears you down by the third day. Plan the itinerary so that the hottest cities come first, while you are fresh, and the cool ones at the end.
Frequently asked questions
How hot is Tokyo in August?
The average high is 31.3°C (88°F) and the low 23.5°C. 30°C is reached on 73% of days, 35°C on 9%, and 47% of nights stay above 25°C. Humidity around 75% pushes the heat index to 35 to 40°C on most afternoons.
Which is the hottest city in Japan?
Among major cities Kyoto and Osaka share the highest August average high (33.7°C); Kyoto reaches 35°C most often (32% of August days). The record temperatures belong to inland Kumagaya and Hamamatsu (41.1°C).
Is Japan hotter than Thailand in summer?
Tokyo’s August high (31.3°C) is close to Bangkok’s (32 to 33°C), and Osaka and Kyoto exceed it. Bangkok’s humidity is similar, so the felt heat is comparable; the difference is that Japan’s heat lasts two months rather than all year.
Is it safe to visit Japan in August?
Yes, with planning. Heatstroke is a real risk for visitors who sightsee through the middle of the day; early starts, indoor afternoons, constant fluids and a hotel with good air conditioning make August manageable. Hokkaido and the mountains are the comfortable alternatives.
When does Japan cool down?
Noticeably after the autumn equinox around 23 September; October is comfortable everywhere (Tokyo high 22°C). Early September is still summer, with typhoons.
- August highs of 31°C in Tokyo and 34°C in Kyoto and Osaka, with 75% humidity: a heat index of 35 to 43°C
- Kyoto reaches 35°C on one August day in three; Osaka has tropical nights on 63% of nights; Sapporo has almost none
- Peak heat: late July to 20 August; relief after the equinox in late September
- Escape to Hokkaido or the Alps; in the cities, move early and late, drink constantly, and choose the hotel for its air conditioning
Sources: Japan Meteorological Agency climatological normals (1991 to 2020) for temperatures, precipitation and sunshine; JMA daily observations 1968 to 2025 (58 years) compiled by this site for the share of sunny, rainy, snowy, hot and cold days. Written by a certified Japanese weather forecaster (気象予報士). Percentages are the share of days in the month; a 30 percent rain-day figure means roughly 9 days a month.