Analysts say August could be disappointing for Detroit's Big Three automakers.
Despite huge cash rebates, sales appear to have been sluggish.
Hurricane Charley also made a dent. Florida is the nation's second-largest market for new vehicles.
Analysts also say many Americans may be postponing big purchases such as new cars and trucks. There are new signs the economy may not be growing as quickly as some predicted.
Already saddled with bloated inventories, General Motors and Ford could be forced to trim fourth-quarter production.
So far this year, Big Three business in the U.S. is off roughly one percent from a year ago. Asian brands have seen a seven percent growth. European nameplates are off five percent.