UPDATE 1-Abercrombie August sales dismay, Aeropostale beat

(Adds Aeropostale executive, analyst, details)

NEW YORK, Sept 4 (Reuters) - Teen clothing retailer Abercrombie & Fitch Co (ANF.N) posted a sharper-than-expected drop in August sales, while rival Aeropostale Inc (ARO.N) extended its winning streak, topping forecasts on back-to- school demand.

Aeropostale has performed relatively well in a U.S. economic downturn and outpaced rivals, who have seen a spate of declining same-store sales, a key measure of retail performance that measures sales at stores open at least a year.

Key to that performance are Aeropostale's prices, which are lower than those at American Eagle Outfitters Inc (AEO.N) and Abercrombie. The company, which is known as for its promotions, has posted robust sales increases in recent months.

"We promote every day," said Chief Merchandising Officer Mindy Meads, during a conference call. "We've been able to find a lot of new promotions ... to mix it up and catch the customers' attention."

Abercrombie shares were down 3.8 percent to $50.90 in late trade on Thursday. Aeropostale, whose shares have risen 36 percent since January, was down 2 percent to $35.17.

Abercrombie recently forecast a disappointing full-year profit and has seen its shares drop 32 percent since the beginning of the year.

The company said its same-store sales fell 11 percent in August. Analysts had forecast a decline of 7.9 percent, according to Thomson Reuters Estimates.

Total sales fell 5 percent to $405.5 million.

Sales at stores appealing to tourists visiting the United States were strong, but failed to offset weakness in sales of its graphic T-shirts to both men and women. Jeans sales performed well for both categories, Abercrombie said.

Aeropostale said same-store sales rose 13 percent, helped by key back-to-school items such as knits, denim and graphic T-shirts.

That was well above the 6.9 percent rise expected, on average, by analysts, according to Thomson Reuters Estimates.

Total sales rose 24 percent for the four weeks ended Aug. 30 to $207.9 million.

"Teen retailers with quality, fashion-right product such as Aeropostale weathered the economic storms," wrote Needham & Co analyst Christine Chen in a note to investors. (Reporting by Sarah Coffey and Alexandria Sage in San Francisco; Editing by Andre Grenon)