Updated from 10:34 a.m. EDTHurricane devastation, high gas prices and unusually warm weather cut into discretionary spending for low- and middle-income consumers in September, but given all the obstacles, retail chains turned in better-than-expected results. Ken Perkins, president of industry tracker Retail Metrics, said his firm's survey of about 100 national retail chains turned up an aggregate same-store sales gain of 4.1% for the month. The result beat expectations for a 3.6% increase. Same-store sales serve as a key measure of a retailer's performance, covering sales at locations that have been open for at least one year. Retail Metrics reported that 63% of retailers in its index beat expectations, well above the long-term average of 54%, while just 35% turned in negative surprises, below the long-term average of 42%. High-end retailers like Neiman Marcus ( NMG.A) remained strong, while teen clothing chains including American Eagle Outfitters ( AEOS) and Aeropostale ( ARO) were mixed. "In a broad sense, this looks like more of the same, but the reality is that these September numbers look a bit more uneven and a bit more noisy than numbers in past months," said Michael Niemera, chief economist and director of research with the International Council of Shopping Centers. "The numbers may overstate the performance," he continued. "Discounters got a nice lift from the 50% increase in gas prices, which inflated their results, but there is downside to those gas prices because they cut into demand." Following the chain-store reports, the sector was stronger. The S&P Retail Index was recently gaining 0.9%, and the Dow Jones U.S. Retail Index was higher by 0.4%. Still, a spate of retailers lowered expectations for earnings in the second half of the year, and the reports failed to quell concerns about a slowdown in consumer spending. The world's largest retailer, Wal-Mart ( WMT), said its same-store sales were in line with estimates, rising 3.8% last month. The company's Wal-Mart stores posted a 2.6% comp-sales increase, while its Sam's Club wholesale clubs recorded 9.8% growth. Total sales rose 9.7% to $28.24 billion.