The problem is that the invasion spawn can move from one city to another during a day (afternoon-evening). Perhaps the best we can do is post a heads-up here on the boards, although I have a feeling that many players don't even read them.
Well - to follow up: Today the 22. of Nov. the crimson has been seen in Trinsic at 18.10 hours.
What I do is to recall around to the various potential cities to check. I know it's a bit of a hassle these days with blocked runes, but moongates are close to at least Skara, Trinsic and Moonglow. Britain can be marked in the area just east of the cemetary. Skara can also be marked just across the boat crossing - at the ranger huts. Vesper can be marked closed to the cemetary as well. FYI.