NEW YORK — Citing the changing winds at the “The Early Show,” weatherman Mark McEwen and the CBS ayemer will be parting company.A veteran of the skein for almost 16 years, McEwen will likely take time off to write a book. He is also said to be in discussions for future projects with the net and its parent company Viacom. His contract ends in October. Insiders say that the decision was mutually agreed upon after the network decided to make significant changes to the format of the program. The net has yet to name its replacement anchors for Bryant Gumbel, who left last May, and Jane Clayson, whose departure was announced thisweek. McEwen’s departure date has not been announced.