Last year's August increase was only 1.3%, the poorest performance that chains turned in all year, so this year's year-over-year comparison could have been strong. But record high gas prices and the 11th-warmest August in over 110 years held back their performance.

Wholesale clubs notched the industry's strongest performance by sector, with a 7.8% increase. Costco led the way, rising 9%, followed by Wal-Mart's Sam's Clubs, which were up 6.6%.

The weakest sector overall was apparel, inching up by 1.2%. Those chain's numbers as a whole were brought down by a 9% drop at Gap Inc. Strong performers in the sector were Abercrombie & Fitch, up 24%, and Chico's FAS, which shot up 14%.