NEW YORK (CNN/Money) - U.S. chain stores posted their first weekly sales increase in a month last week, as consumers headed to the malls to do some Labor Day holiday bargain hunting, according to an industry report out Wednesday.

But that doesn't mean a rosier outlook for the fall season.

Retailers have seen deteriorating sales during the last few months as the combined effects of uncertain economic news, a seasonal shift to fall merchandise, and heat waves tamed consumers, whose spending has been shoring up the economy.

Some retailers are nervous heading into the crucial fall season as early reads on back-to-school sales are disappointing, prompting many chains to offer early promotions on clothing and other related back-to-school merchandise.

Sales at stores open at least a year, a key gauge known as same-store sales, increased 0.5 percent for the week ending Aug. 31 compared with the previous week, the Bank of Tokyo-Mitsubishi and UBS Warburg reported Tuesday.

Separately, Instinet Research's Redbook U.S. Chain Store Index fell 1.7 percent in the first four weeks of August compared with the same period a month ago.

"Back-to-school sales have not been meeting expectations, especially in the apparel and accessories merchandise classifications," the report said. "Most stores missed or appeared at the lower end of their targets."

The reports come a day before the bulk of the nation's retailers report August same-store sales results. The Bank of Tokyo is forecasting a "recession-like" 1.5 percent increase, which is the worst monthly sales performance since September, 2001, when sales grew just 0.9 percent.

Separately Wednesday, several retailers reported August sales results a day early.

CVS Corp. (CVS: Research, Estimates), the nation's second-largest drug store chain, said August same-store sales increased 7.9 percent from a year earlier.

Women's apparel retailer Christopher & Banks Corp. (CBK: up $1.05 to $29.05, Research, Estimates) said a 6 percent rise in August same-store sales would help it post higher second-quarter earnings of 25-to-26 cents a share, up from 20 cents a share a year earlier. Analysts polled by earnings tracker First Call anticipate a profit of 26 cents a share.

Another women's clothing chain, AnnTaylor Stores Corp. (ANN: down $0.14 to $24.90, Research, Estimates), said Wednesday that August sales at stores open at least a year fell 7.6 percent, but said full-price selling at its flagship stores picked up late in the month.

The company also said it was comfortable with third-quarter earnings guidance of 50 cents to 51 cents. The average analyst estimate is 50 cents, according to First Call.

Costco Wholesale (COST: up $0.85 to $33.36, Research, Estimates), which operates discount warehouse stores, on Wednesday reported that sales at its stores open at least a year rose six percent from a year-ago in August.

And The Children's Place Retail Stores Inc. (PLCE: down $0.70 to $17.90, Research, Estimates) reported a 16 percent decline in its same-store sales, sharply lower than the 9 percent decline it posted in the year-earlier period.  

-- Reuters contributed to this report.