DETROIT ( TheStreet) -- Not surprisingly, September auto sales will show a dip, but it could be less dramatic than anticipated.

A forecast by Santa Monica, Calif.-based TrueCar, which aggregates vehicle sales information, suggests that September sales will decline 7% from September 2008 and 29% from August 2009, when Cash-for-Clunkers energized auto sales. A total of 899,374 units would bring domestic auto sales to a seasonally adjusted annual rate of 11.1 million units.

"As expected, new-vehicle sales are down dramatically from August, but the declines will not be as bad as it looked at the beginning of the month," said Jesse Toprak, TrueCar vice president of industry trends, in a prepared statement. "Fundamental macroeconomic forces that fuel car sales have shown relative improvement within the last several weeks, although we are still a long way from a full recovery." He said domestic manufacturers' market share will be a record low 40.2%.

The month's winners were Nissan ( NSANY) , with sales up 27% from September 2008; Honda ( HMC), with a 13% increase, and Ford ( F) and Toyota ( TM), each up 12%, TrueCar estimates.

Meanwhile Chrysler is showing a 41% decline while General Motors is expected to show a 40% decline. Every manufacturer showed a decline from August 2009: Ford showed the smallest decline, down 26%.

As for market share, Toyota showed the biggest increase from September 2008, with an 18% share, up 3%. Ford was second with a 2.3% increase to a 14.2% share.

-- Written by Ted Reed in Charlotte, N.C. .

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