after the warning was raised, a record high.

[Maybo]

It recorded a rainfall of 158.1 millimetres in the hour after the warning was raised, a record high.

Source: At least 2 dead after Hong Kong battered by record rainfall, severe flooding by HILLARY LEUNG

Is "which is" omitted in the above sentence?

It recorded a rainfall of 158.1 millimetres in the hour after the warning was raised, (which is) a record high.

 

[Tarheel]

No, it is not. Nothing is omitted. In fact, it is perfectly clear in the original that that number refers to the amount of rain that fell in that time period.

 

[Maybo]

No, it is not. Nothing is omitted. In fact, it is perfectly clear in the original that that number refers to the amount of rain that fell in that time period.

When can I use this kind of sentence structure “xxxxx, a noun”?

 

[Tarheel]

There are a million possibilities. Do you have something in mind?

 

[Maybo]

There are a million possibilities. Do you have something in mind?

Can I say “Peter has broken 10 records in running competitions, a great athlete”?

 

[Tarheel]

No, that doesn't work. Perhaps:

Peter is a great athlete. He is a runner who has broken ten records.

While "running competitions" is not wrong, it is entirely unnatural. Say "races" instead.

 

[Maybo]

No, that doesn't work. Perhaps:

Peter is a great athlete. He is a runner who has broken ten records.

While "running competitions" is not wrong, it is entirely unnatural. Say "races" instead.

Then when can I use this sentence structure "XXXXX, a noun"?

 

[Tarheel]

Peter, a runner, is a world class athlete. He has set set several records.

That's one possibility among many.