In a note to clients — as reported by “AppleInsider” (http://www.appleinsider.com) — BMO Capital analyst Keith Bachman said he expects Apple to post a “significant miss”for its fourth fiscal quarter of 2012 as Mac sales continue to be cannibalized by the company’s iPad tablet line.

Despite raising sales estimates for both the iPhone and iPad, he said the June quarter and upcoming final fiscal quarter of 2012 will be “challenging” for Apple as the tech company Apple could see an US$5.5 billion miss from the $38.5 billion consensus for the company’s fourth fiscal quarter ending in September if its third quarter performance is in line with the current $37.5 billion forecast, according to historical patterns and outlooks.

Bachman says his Mac sales estimate is expected to drop 1.6 million units over the same six quarter period. He dropped his Mac sales estimate from 18.65 million units to 18.22 million for 2012 and sees that decline carrying over into 2013 which slipped to 20.18 million from 21.38 million.