It began to rain hard.

开始下大雨了。

It began to rain hard.

的翻译是：它就开始下雨。

I'll be back tomorrow if it doesn't rain hard.

如果天不下大雨的话，我明天就回来。

I was just about to go out, when it began to rain hard.

我正要出门的时候，天空开始下起了大雨。

It is rain hard, but we get there in time all the same.

那时正下着雨，我们还是准时到达那里。