Sometimes the 'heavens open' and there may be a period of extremely heavy rainfall in a short period of time - possibly leading to flash floods and destruction. If you like statistics you may wish to explain exactly how much rain fell within a period of time.
3 months worth : 三ヶ月分
One day: 一日
There was 3 months worth of rain in one day.
三ヶ月分の雨が１日に降った
In just one day there was 3 months worth of rain.
たった1日で三ヶ月分の雨が降った
最初の答えはそのままですね。最後の答えはjust「たった」を入れることでちょっとドラマティックになります。
例：
In just one minute, he finished the entire bowl of ramen.
たった1分で彼はラーメン一杯を全部食べた。
In a space of just 2 meters, she grew a beautiful vegetable garden.
たった二メートルのスペースで彼女は綺麗な野菜ガーデンを育てました。
Within 24 hours 3 months worth of rain had fallen.
1.
Here we are saying that there was three months worth of rain that fell in a single day.
2.
The second phrase shows that within a 24hour period that alot of rain had fallen.
Both phrases are similar in that they are saying exactly the same thing. Both would be used in a more formal area.
It rained about three months worth of rain in one storm.
"We got about three months of rain in one day." Here your just saying that you had approximately or about three months worth of rain come down in one day.
"It rained about three months worth of rain in one storm." Worth here is just a measure word for the amount of rain that occurred. For example: The pay check she received was worth twice as much as pervious pay checks.
"We got about three months of rain in one day."（およそ3カ月分の雨が一日で降った）
- ここでは、およそ3カ月分の雨が一日で降ったと伝えています。
"It rained about three months worth of rain in one storm."（一度の嵐でおよそ3カ月分の雨が降った）
- "Worth" はここでは、降った雨の量を表しています。
例えば：
The pay check she received was worth twice as much as pervious pay checks.
（彼女はそれまでの倍の給与を受け取りました）
There was three months worth of rain in a single day.
In just one day there was 3 months worth of rain.
We had 3 months of rainfall in one day.
To have '3 months worth' of something means that you have a lot of it. If there was three months worth of rainfall in one day then it rained very very heavily.
Some ways of saying this are:
There was three months worth of rain in a single day.
In just one day there was 3 months worth of rain.
We had 3 months of rainfall in one day.
Three months worth'（三カ月分）は「たくさん」を表します。
一日に 'Three months worth'（三カ月分）の雨が降ったのなら、それは「雨がたくさん降った」ということです。
これは、例えば次のような言い方ができます。
There was three months worth of rain in a single day.（たった一日で三カ月分の雨が降った）
In just one day there was 3 months worth of rain.（たった一日の間に三カ月分の雨が降った）
We had 3 months of rainfall in one day.（一日で三カ月分の雨が降った）
The way to describe the amount of rain that we have is called 'rainfall' as it falls from the sky
you can say 'one day' or a single day' as single means one as well
「雨の量」は 'rainfall' と言います。雨は空から 'fall'（降る）するからです。
「一日」は 'one day' かあるいは 'a single day' と言えます。'single' は「1」の意味です。
イギリス 
日本 
カナダ 
アイルランド 
