Apple could sell as many as 51.5 million iPhones during the holiday quarter, says Canaccord Genuity analyst Michael Walkley. In an investors note out Tuesday, Walkley said he expects strong sales of the iPhone 5S through December as Apple bumps up supply to meet the heavy demand. The more expensive 5S is currently outselling the 5C by a ratio of 2.5 to 1, according to the analyst. Apple reported total iPhone sales of 33.8 million iPhones last quarter and 47.8 million in the final quarter of 2012. iPad sales were soft last quarter, Walkley said. Apple sold only 14.1 million tablets as buyers held off purchases in anticipation of the new models announced last week. But holiday shoppers should provide a hefty increase this quarter when Apple is projected to sell 24.2 million iPads. The analyst believes more consumers will opt for the iPad Air as a holiday gift.