At a time when Apple (NASDAQ:AAPL) is highly rumored to introduce two iPhone models -- the flagship iPhone 5S and the low-cost iPhone 5C -- at a media event on Sept. 10, an analyst has predicted that the latter will outship the high-end model of the handset in the third quarter of this year.

Apple is expected to ship 8.4 million units of the iPhone 5C in the September quarter, while shipments of iPhone 5S could be limited to 5.2 million units during the same period due to difficulties in building the device, according to a research note from Ming-Chi Kuo of KGI Securities.

However, Kuo said the iPhone 5C, which may feature a plastic frame, is not likely to be the best-selling iPhone model for long as shipments in the fourth quarter are likely to grow only by 122 percent, compared to an estimated 438 percent jump for the iPhone 5S.

Kuo believes that the iPhone 5C’s shipments will grow to 18.7 million units in the December quarter, while shipments of the iPhone 5S will reach 28 million units during the holiday season.

“Despite yield rate issues with fingerprint sensor module and casing, a timetable ensuring improvement has been established, which eases our concerns over 5S production,” Kuo was quoted by AppleInsider as saying. “We hold a positive view on growth momentum along the iPhone supply chain, for which we expect a jump from August followed by sustained growth into September and (the fourth quarter of fiscal 2013).”

According to Kuo, total iPhone shipments are expected to reach 35 million units in the third quarter -- a 30 percent increase over the same period in 2012 -- and rise to 55 million in the fourth quarter.

No More iPhone 5?

In his note on Monday, Kuo forecast that the new iPhone 5C will replace the existing iPhone 5, and feature largely the same components as its predecessor. It could be made available as the mid-range model in the iPhone lineup, while the iPhone 4S will fill the slot of an entry-level iPhone.

The analyst also talked about the expected price range of the plastic iPhone. According to him, the iPhone 5C could cost between $400 and $500 without a contract, while the iPhone 4S is likely to be offered between $300 and $400.

Kuo’s claims contradict some earlier reports, which suggested that the iPhone 5C would replace the iPhone 4S as the entry-level model in the iPhone lineup as Apple wanted the larger 4-inch display and the lightening connector on all the iPhone models available in the market.

Rumors have it that the iPhone 5C will be powered by an A6 processor, and will feature a 4-inch retina display. The iPhone 5S, which is expected to be the company’s new premium smartphone, will likely sport an A7 processor, a fingerprint sensor beneath the home button and a dual LED flash component as its key features.

The iPhone 5S is also rumored to be available in a golden or champagne color, as the third color variant in addition to the standard black and white versions.