UPDATE 1-JD Power-LMC Automotive see Sept US auto sales up 11 pct

* LMC sees 2012 U.S. auto sales at 14.3 million vehicles

* LMC sees 2013 U.S. auto sales at 15 million vehicles

* Sedan retail sales strong in September

Sept 20 (Reuters) - U.S. auto sales in September will rise 11 percent from a year ago, consultancies J.D. Power and LMC Automotive said on Thursday.

U.S. sales will show a seasonally adjusted annualized rate of 14.5 million vehicles in September, the same pace as was seen in August.

LMC maintained its forecast for full-year U.S. auto sales at 14.3 million new vehicles, which would be a 12 percent rise from 2011 sales.

American consumers are opting for smaller sedans than they were a year ago, J.D. Power said. Subcompact, compact and midsize sedans are each expected to show retail sales gains of 25 percent.

LMC Automotive raised its 2012 retail sales outlook to 11.6 million vehicles, from 11.4 million vehicles. It forecast September U.S. retail sales to rise 12 percent from a year ago.

Retail sales are lower that total light vehicle sales because they do not count fleet sales to rental agencies, businesses and government.

LMC said that auto sales in the coming months may be more volatile than they have been in the past few months.

"During the next few months, car buyers will be processing further economic news, additional details on the European crisis, as well as the forthcoming presidential election, likely creating an environment with higher volatility," said LMC forecaster Jeff Schuster.

For 2013, LMC maintained its total light vehicle sales outlook at 15 million vehicles, and 12.3 million for retail sales.

Earlier on Thursday, Edmunds.com also forecast 2013 light vehicle auto sales at 15 million. Edmunds' forecast for 2012 U.S. auto sales is 14.4 million.