That doesn't mean it will reach all the way up to Michigan when it's still in LA. Just read the text in the black box --"Probability that the center of Katrina will pass within 75 statute miles during the 72 hours starting at 1:00PM CDT Sun Aug 28 2005".
I'm not buying these maps. Specifically, they don't curve enough eastward at the north end to make sense. I suspect the hurricane tracking maps are not taking the jetstream into account, since hurricanes aren't normally an issue far enough north to be affected by the jetstream.