I have been reading about the Panda Update going to be on a rollout launch in the year to come. As a webmaster, how do I know for sure that my website has been struck by the Panda update? Does a warning message show up in my GWMT?
There is no warning in GWT specifically. You may get an unnatural links warning if that is one of your issues but otherwise the penalty is silently applied. You'll know when you get eaten by the Panda because your inbounds from Google will drop like a rock.