The number represents the % of Stagger
At Low Stagger the Bar turns Green.
At Medium Stagger the Bar turns Yellow
At High Stagger the Bar turns Red.
I did not create this weakaura but since I can't remember where I got it from originally I have uploaded it here for those that keep asking me for it.
Stagger background 2 (aurabar)
Stagger p 2 (aurabar)
Stagger text 2 (text)
Light Stagger 2 (aurabar)
Moderate Stagger 2 (aurabar)
Heavy Stagger 2 (aurabar)
Paused stagger trigger 2 (text)