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Watch out for the torrential rain - Guerrilla-gohu and Oh-ame

In the summer season, what you keep in mind during your travel in Japan is probably typhoons that sometimes come up from the Pacific Ocean. Also, you should watch out for Guerrilla-gohu and Oh-ame heavy rainfalls, tend to happen more frequently than before.

What’s Guerrilla-gohu and Oh-ame?

Guerrilla-gohu ゲリラ豪雨 is a downpour; the heavy rain suddenly and intensively falls as if it was a Guerrilla attack. Oh-ame 大雨 literally means “big rain”, the rainfall that is not raining all of sudden but so heavily, cats and dogs.

How to cope with Guerrilla-gohu and Oh-ame on your trip in Japan

Typhoons and Oh-ame are rather predictive, and you can find when and where to avoid staying beforehand. However, forecasting a Guerrilla-gohu is not easy as it usually occurs all of sudden, it involves more chances that tourists encounter disasters.

Check wheatear forecasts frequently while on your trip

Check weathercasts frequently while on your trip
Both Guerrilla-gohu and Oh-ame often occur at the point where a mass warm air meets a mass of cold air. Knowing the movement of air masses will help you expect the risk.

Check the nearest evacuation places for emergency

School buildings, community centers, commercial facilities, etc.

Japanese Sample
Is there a place I can evacuate near hear?

Get away from riverside, as quickly as possible

The water level of the river will quickly rise as the intensive rainwater is coming down from the upper stream. If a flood occurs, it is hard to distinguish rivers and roads, and you will lose a way to evacuate. On a river site in a mountain area, you should also keep in mind the discharge of water from a dam.

Get out of the valley once it begins raining, as soon as possible (On hiking in mountains)

Even if it is not much raining at the site you are, the chances are that it is heavily raining at upper sites on the mountain, causes a flood on the valley you are. A flash flood may also happen if a landslide occurs.

A caution board that tells it alarms when a water discharge of dam is conducted.

A caution board saying "the water level of this river may suddenly increase".

It is so risky to move out of a building at night or when a flood has already happened

You may fall down a manhole, get flowed into the river, and get injured by flood drifts. If you find yourself too late to evacuate, try not to take a risk and stay in a safe place as possible as you can.

At a building near mountains, avoid staying in a room on the side of mountain slopes

The heavy rain may cause landslides on mountains, causes large rocks rolling downhill. If you have to stay in a building beside a mountain, evacuate in a room on the opposite side of the mountain slopes.

Stay on the second floor of buildings

Once a flood occurs, the first floor (ground floor) can easily get flooded. Water floods into rooms very quickly, maybe much quicker than you expect.

If you need to drive a car in the middle of/after the torrential rain, watch out for road conditions

You can hardly tell the depth of water on flooded roads, especially slope roads which are often covered with water at the bottom, looks like a flat road where vehicles can go through, but cannot. The car traveling the sloping road gets under the water at the bottom where the driver cannot open doors due to water pressure. In this case, the driver needs to break the window glass with something like a hammer and get out of the water. If the driver has nothing to break the glasses, the driver needs to wait while inside of the car is filled with water so that it enables to open the door manually, usually at the very last minutes, in a touch-and-go situation before the car fully gets sunk.

Related Japanese words and phrases

ゲリラ豪雨 (Guerrilla-gohu)
Sudden downpour

ゲリラ雷雨 Guerrilla-raiu)
Sudden thunderstorm

大雨 Oh-ame
Heavy rain, Downpour


Torrential rainfall


土砂災害(Dosha Saigai)
Landslide disaster

Temporary evacuation area

Is there a place I can evacuate near hear?

警報レベル(Keihou reberu)
Alert Level

Level 1 レベル1 - 大雨注意報(Oh-ame Chuuihou):Advisories
Level 2 レベル2 - 大雨警報(Oh-ame Keihou):Warnings
Level 3 レベル3 - 大雨特別警報(Oh-ame Tokubetsu Keiho):Emergency Warnings

About disaster alert by Japan Meteorological Agency (In Japanese)

Japan Meteorological Agency Website

Check the water level in rivers in Tokyo

TOKYO METROPOLITAN GOVERNMENT operates real-time monitoring system and offers information on rainfall and the water level in rivers.
Twitter: @tokyo_suibo

Last updated : May 2018
This article is also available in Japanese : Watch out for Oh-ame and Guerrilla-gohu

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