When planning a trip to Japan, most travelers imagine cherry blossoms in spring, vibrant festivals in summer, or colorful leaves in autumn. However, one weather phenomenon that often catches tourists off guard—especially in the warmer months—is the guerrilla rainstorm, known in Japanese as “ゲリラ豪雨” (gerira-gōu).
These sudden, intense downpours can flood streets, halt trains, and even damage property, all within a short period of time. Here’s what you need to know to stay safe and dry during your visit to Japan.
What Is a Guerrilla Rainstorm?
A guerrilla rainstorm is an unpredictable, short but extremely heavy localized rainstorm that often occurs in the late afternoon or early evening, especially in the summer months (June to September). The term comes from the idea that these storms “attack” suddenly and without warning—much like guerrilla warfare.
Unlike typical rainy weather that’s forecast days in advance, these storms can form within 30 minutes and may only affect a small area, such as one neighborhood or city block.
Real-Life Example: Shibuya Flooded in 30 Minutes
On August 1, 2023, a powerful guerrilla rainstorm struck central Tokyo around 5 PM. In areas like Shibuya and Shinjuku, heavy rain fell at over 80 mm per hour. Streets turned into rivers, some subway entrances were temporarily closed, and tourists were left stranded without umbrellas.
One American visitor wrote on social media:
“We were taking photos in front of Hachiko, and then BOOM—it was like someone dumped a pool on us. We ran into a café completely soaked. It wasn’t in the forecast!”
Why Do Guerrilla Rainstorms Happen?
Japan’s humid summers combined with high temperatures and complex terrain (mountains, valleys, and coastlines) create perfect conditions for localized storm clouds to form rapidly. Urban heat islands—especially in major cities like Tokyo, Osaka, and Fukuoka—also contribute.
These storms are not typhoons, but can be just as dangerous in the short term.
How to Protect Yourself as a Tourist
1. Always carry a compact umbrella or rain poncho
Even if the sky looks clear in the morning, conditions can change fast. Many convenience stores sell affordable umbrellas.
2. Download Japanese weather apps like “Tenki.jp” or use Google Weather
Apps often send real-time rain alerts, especially when rain clouds form near your current location.
3. Know where you are
If you’re near a river, underpasses, or low-lying areas, move to higher ground when a storm begins. Flooding can occur within minutes.
4. Avoid using elevators in outdoor areas during storms
Some underground mall entrances flood easily. Wait in nearby stores or cafes until the rain stops.
5. Public transport delays
Rainstorms often cause train delays or suspension, especially in suburban areas. Check train apps like “Navitime” or “Japan Transit Planner.”
Bonus Tip: Don’t Be Surprised by Vending Machines with Umbrellas
Japan is famous for its vending machines, and some areas—especially in cities—now offer emergency umbrella vending for about 500 yen. It’s a testament to how common and sudden these storms are.
Final Thoughts
Guerrilla rainstorms are one of the lesser-known parts of Japan’s climate, but they don’t have to ruin your trip. With a little preparation and awareness, you can enjoy your journey—whether rain or shine.
So next time you’re walking around Kyoto’s temples or shopping in Harajuku, keep an eye on the sky… and maybe that weather app, too.
Stay safe and travel smart!