[tejtm]

CME are "Coronal Mass Ejection" with mass being the operative word here. Electromagnetic radiation (electrons photons) can make the trip between sun and earth in about 8 minute but anything with neutrons or protons (such as the coronal plasma) takes much longer as in, a day and a half to several days. CME are not hard to spot leaving the sun with even with tiny amateur telescopes (the sun does not require much in the way of light gathering) so even without the professional scopes (SOHO) with dedicated satellites leading and trailing earth orbit constantly viewing around the edge of the sun as seen from earth or being able to acoustically "hear" (if you can call 5 minute pressure waves sound) the far side of the sun, it is not conceivable to me we would not be warned a CME was incoming, doing something about it is another story.