Sterne Agee analyst Shaw Wu increased his September quarter iPhone shipment estimate from 26 million units to 27 million units Tuesday. It’s the second bump in Wu’s estimates since the iPhone 5 was announced. Wu said he’s also upping his December quarter forecast from 46 million units to 46.5 million units due to “our continued supplier checks indicating production constraints on new in-cell touchscreens.”

“We find it interesting that many tech blogs and reviewers panned the iPhone 5 saying it “lacked the wow factor” similar to the iPhone 4 that was plagued by “antenna-gate” and the iPhone 4S which was a relatively “minor” and “disappointing” update with Siri as the key new feature,” Wu wrote in a note Tuesday morning. “The previous iPhones went on to sell record number of units and we believe iPhone 5 will likely see a similar result. We continue to believe iPhone 5 will put a lot of pressure on competitors where it will incrementally capture a portion of customers attracted to Android/Windows smart phones with larger screens and/or 4G LTE wireless.”

Wu said he believes that pundits are underestimating the iPhone 5 “in that it is a significant update and will drive a powerful product cycle.”