When it rains very hard, we say "it's raining cats and dogs".
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A : What's that sound?
B : It's raining cats and dogs!
A : I will have a look through the window.
もし土砂降りの雨が降ったら"it's raining cats and dogs"と言います。
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A : What's that sound?
（何の音？）
B : It's raining cats and dogs!
（土砂降りの雨が降ってるよ）
A : I will have a look through the window.
（窓からのぞいてみよう）
A torrential downpour is very heavy rainfall in which you would get soaked immediately. 'Localised' means in a certain, finite area, or possibly the area in which the speaker or the announcement is being made.
"I'm not going out walking today. The weather forecast is for torrential downpour in places."
"A torrential downpour "(ゲリラ豪雨)は
すぐにびしょ濡れになってしまうとても激しい豪雨のことです。
"Localized"はある特定の地域や、その話し手がいる場所を指します。
"I'm no going out walking today.
The weather forecast is for torrential downpour in places."
(今日はでかけません。天気予報が各地でゲリラ豪雨です。)
A localized downpour of rain flooded streets in Gifu.Nagoya was unaffected!
Rain can often fall in just one area and not in another close by ...this is known as: " localized rain" And "a downpour " implies heavy rain...So in this case:
"A localized downpour of rain flooded streets in Gifu.Nagoya was unaffected!"
ある地域のみ雨が降ってほかは降っていないということがしばしばあります。このことを " localized rain" や "a downpour " と言います。 "a downpour " は激しい雨を意味します。この場合、次のように言えます。
"A localized downpour of rain flooded streets in Gifu.Nagoya was unaffected!"
（岐阜でゲリラ豪雨でしたが、名古屋は大丈夫でした。）
This is a Japanese expression.
It's used to describe heavy rainfall for a short period of time.
It's not commonly experienced.
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Example
A: What caused the flooding in Japan?
B: Guerrilla rainfall
これは日本語の言い回しです。
短時間に降る土砂降りの雨の事を言います。
あまりよく経験することではありません。
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例
A: What caused the flooding in Japan?
(日本での洪水は何が原因ですか？）
B: Guerrilla rainfall
(ゲリラ豪雨です）
These phrases are used when it is or had been raining very hard,
for example
"there will be sudden down pours forecasted for tommorow".
"Expect to see heavy showers today, the weather is going to be terrible".
アメリカ合衆国 
日本 
南アフリカ 
ニュージーランド 
イギリス 
