SAN FRANCISCO -- Warm temperatures are getting the blame for potentially weak sales at chain stores in September, but the troubled economy isn't helping either.

Most retailers will report their September sales data on Thursday morning, and overall expectations are low. Already, retail giants Target ( TGT) and Lowe's ( LOW) have warned of weaker-than-anticipated results for the period, and analysts expect the numbers to show the seventh straight month of slowing growth.

According to Thomson Financial, the nation's top retailers are expected to post a collective 2.3% rise in September same-store sales, or sales at stores open at least a year. That's down sharply from a 6.3% increase last year.

Those estimates exclude giant Wal-Mart ( WMT), which tends to skew results. When factoring in the world's largest retailer, the prediction for September sales growth falls slightly, to 2.1%, vs. a 4.2% increase last year.

On Wall Street, the usual suspects --weather and economic worries -- are being held responsible for the drop.

Kimberly Greenberger, an analyst for Citigroup, said she remains cautious on September sales as slowing consumer traffic, high gas prices and warm temperatures will likely crimp results.

"We are most cautious on retailers with high levels of wintry apparel given warmer temperatures," she wrote in a research report, pointing specifically to J. Crew ( JCG) emphasizing coats and outwear; Children's Place ( PLCE) focusing on coats; and Pacific Sunwear ( PSUN) carrying a lot of fleece goods.

Shares of Children's Place already took a hit on Tuesday, tumbling 6% after the kids' clothing seller reported a 3% slide in September same-store sales and slashed its guidance.

Greenberger noted that September had been the fifth warmest and 12th driest month in 113 years, forcing retailers to knock down prices on fall merchandise. She added that clearance levels at American Eagle ( AEO) and Limited Brands ( LTD) were of particular concern.

Mark Montagna, vice president for CL King & Associates, also took note of the promotional environment in the specialty sector.

"This likely means the sector will have an overall margin decline on a year-over-year basis," he wrote in his research. "It likely will lead to October being highly promotional as retailers try to flush out the fall deliveries to make room for new Christmas and winter deliveries."

While weather may play a role in sales, Mike Niemira, chief economist for the International Council of Shopping Centers, says the effects are minimal. For September, it will influence same-store sales by only a half percentage point, he says.

The slowing economy and housing slump, rather, are a much greater factor in the disappointing numbers.

The weather is "only significant on the weak underlying trend, so it seems more pronounced," says Niemira.

Indeed, same-store sales, or comps, have grown at a much slower rate over the past several months than last year. Overall, they have climbed an average of 2.4% between February and August, compared with a 3.9% rise last year in the same period.

September, with its continuation of back-to-school sales, is the third-most important month of the year for retailers, behind December and June. On average, it accounts for about 9% of retailers' annual sales.

The International Council of Shopping Centers predicts retailers will show a 2% climb in same-store sales for September, which Niemira says does not bode well for the near term.

"Retailers are much more vulnerable," he says. "Some are repositioning, thinking about price points. It's a tougher environment."

Although Niemira acknowledges that lower price points may squeeze margins, he says retailers have little other choice than to discount.

"It's probably still the smarter way to go in the current economic environment," he says.

Still, the outlook for retailers may not be entirely dismal. In August, sales managed to top expectations . And employment -- the economic factor most closely tied to consumer spending -- held up strongly last month.

In addition, Niemira points out that retailers should see a somewhat easier same-store sales comparison from October through December compared with last year in the same period, when the numbers first began to slip.

Luxury retailers are very insulated from economic pressures, and so should perform strongly in September. Analysts predict same-store sales at upscale department store Saks ( SKS) climbed 9.3% in September, while Nordstrom's ( JWN) comps are expected to show a 5% rise.

Teen retailers are expected to see only a 0.2% uptick in same-store sales. American Eagle is expected to post an increase of 1.2%.

Christine Chen, an analyst for Needham & Co., remains positive on teen retailers' performance in the month, despite the unseasonable weather.

"We remain convinced that teens will continue to spend in (the second half of the year) as a result of must-have fashion items in key categories such as dresses, knit tops and denim," she says.

Discount chains are expected to report 2.4% same-store sales growth, or 3.9% excluding Wal-Mart. That compares to a 2.3% climb last year, or 4.5% increase without Wal-Mart.

Wal-Mart projects 1% to 3% growth in September same-store sales, in line with analysts' expectations of 1.9%. Target lowered its forecast to a 1.5% to 2.5% rise, while Wall Street expects it to post a 2.2% gain.

Niemira does not expect the shopping outlook to change much for the crucial holiday season ahead, unless the economy deteriorates rapidly between now and then.

"What you see now is likely the holiday season you'll see later," he says. "The overall pace will not be terribly different."

Check out this list of retail-stock portfolios on Stockpickr by clicking here.

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