Japan’s rainy season (梅雨, tsuyu) runs approximately June 8 to July 21 in Tokyo (varies by region and year), bringing high humidity (85–95%), frequent rain, and major mold risk. Essentials: a good umbrella (not a travel umbrella — a real one), a dehumidifier or silica gel packs, anti-mold spray for bathroom grout and window frames, and preparation for clothes that won’t dry. Mentally: the grey skies compound expat seasonal mood dips — build outdoor activities for the breaks in rain.
Week three of tsuyu. Your towel smells. Your walls have a new smell. Your shoes have white patches. Your phone’s humidity warning has been going off daily.
Nobody told you about this part of Japan.
Japan’s rainy season is one of the most distinctive seasonal experiences of living here — and one of the most challenging for newcomers. It’s not just the rain. It’s the combination of relentless grey skies, humidity that makes you feel like you’re breathing soup, and a specific type of mold that appears on everything you own.
Here’s how to get through it.
When Is Tsuyu?
| Region | Typical Start | Typical End |
|---|---|---|
| Okinawa | Mid-May | Late June |
| Kyushu / Shikoku | Early June | Mid-July |
| Honshu (Tokyo/Osaka) | Early June | Late July |
| Hokkaido | No rainy season | — |
The Japan Meteorological Agency officially declares tsuyu start and end dates. 2025 dates varied from historical averages due to climate shifts.
Hokkaido residents: you’re exempt. Everything north of Aomori largely skips tsuyu.
What Tsuyu Actually Feels Like
Humidity: 85–95% relative humidity for weeks at a time. If you’re from a dry climate, this is oppressive. Even people from tropical climates find Japan’s tsuyu humidity unpleasant because it combines with moderate temperatures (20–28°C) to create sticky, stifling air.
Rain pattern: Not constant rain — alternating grey overcast days, heavy rain days, and brief clear windows. The unpredictability is part of the psychological challenge.
Effect on your apartment: Condensation on windows, dampness on walls, musty smell, and mold growth — especially in poorly ventilated areas.
The Mold Problem
This is the practical issue that surprises foreigners most.
High-risk zones in your apartment:
- Bathroom grout and ceiling
- Under the sink
- Behind large furniture placed against exterior walls
- Window frames
- Inside closets (especially traditional Japanese oshiire closets with futon storage)
- The back of the washing machine
Prevention:
- Run the bathroom fan for 30–60 minutes after every shower, every day
- Leave closet doors slightly open to allow air circulation
- Use silica gel dehumidifying packs in closets and shoe cabinets
- Buy a dehumidifier (除湿機) — genuinely worth it; Japan makes excellent ones
- Anti-mold spray (防カビ剤): apply to bathroom grout before the season starts
If mold appears:
- Wipe with diluted bleach (カビキラー is the standard Japanese mold killer)
- Improve ventilation
- Move furniture away from exterior walls
Essential Tsuyu Gear
Umbrella: Japan is a nation of serious umbrellas. Buy a proper folding umbrella or a longer one — the flimsy travel umbrellas survive one significant tsuyu downpour. Konbini umbrellas (¥500–700) work as backups. Your main umbrella should cost ¥2,000+.
Waterproof shoes / boots: A pair of waterproof shoes or ankle boots changes your daily experience significantly. Japanese brands like Moonstar, GORE-TEX-lined shoes widely available.
Rain jacket / poncho: Essential for cycling or outdoor work. Japan sells lightweight bicycle-riding ponchos at hardware stores.
Dehumidifier: If your apartment lacks an air conditioning unit with dehumidify mode (除湿, joshitsu), a standalone dehumidifier costs ¥15,000–25,000. Run it during peak humidity periods.
Clothes drying: Without a dryer, tsuyu creates a laundry crisis. Options:
- Dry inside with the air conditioner on 除湿 mode
- Coin laundry dryers (コインランドリー) — ¥100–200/8 minutes
- Quick-dry fabric clothing becomes your wardrobe priority
Managing the Psychological Effect
Weeks of grey skies affect mood — more than most people anticipate. The combination of limited sunlight, high humidity discomfort, and staying indoors more correlates with mood dips that can worsen culture shock or expat loneliness.
What helps:
- Get outside during the breaks in rain — even 30 minutes of daylight significantly helps
- Hydrangea viewing (あじさい): Japan’s rainy season flower is beautiful; major gardens hold events
- Treat indoor time as a project: new recipes, language study, hobby time
- Light therapy lamp if you’re from a northern country and affected by light reduction
After Tsuyu: Natsu (Summer)
When tsuyu ends, it ends suddenly. One day it’s grey and damp, the next it’s blazing hot and humid. Japan’s summer (August–September) arrives aggressively. Your reward for surviving tsuyu is a new challenge: 35°C + 80% humidity.