How can I tell whether the meteors are doing any damage to the messenger in Act 3?

This is the messenger you have to steal notes from in Act 3.

After a few attacks, I figured out the idea behind it all. The messenger summons meteorites and teleports away if you get too close. So I stand in the spot he's going to next appear, wait for a red circle to appear and then rush towards him. The idea being that the meteor will hit him.

However, the messenger has no health bar. Also, he doesn't do anything to indicate a hit. I can't see if it's having any effect. How do I know for sure it had effect? Does it really need to be spot on?

EDIT: The solution appeared to be using Yrden to trap him in place, they slay him. Here I was thinking the developers had come up with a nice trick of using an enemy's weapon against him.

I know who you're talking about.

The Quest you're talking about is The Messenger.

The way you described is not how you defeat this guy.

He always teleports to the same places right? So you see him go to a place make him teleport to another. Then you place a Yrden trap there.

Then you just wait and dodge the meteors until he reaches that spot and gets trapped. Do this over and over until you kill him.

Good luck for the fight (although I assume you have already passed it)

PS:

For the record you can see a guide for the Quest here