U.S. new-car sales showed improvement in the first half of September as the recovering inventory of cars helped bring buyers back into the market, according to research firm J.D.Power and Associates. The sales rate for September on an annual basis looks set to reach 12.9 million vehicles, compared with the 12.1 million rate in August. The sales rate in September 2010 was 11.7 million vehicles. After weaker-than-expected demand in May and June, overall vehicle sales in July and August finished better than expected, each topping the 12 million annual sales rate. Japanese automakers have been increasing their inventory of cars, after suffering from a shortage of parts caused by the March earthquake and tsunami in Japan. Nevertheless, analysts and industry observers worry about the prospects for a double-dip recession and whether automakers may be forced to boost retail incentives to keep buyers coming into dealer showrooms. For the year, J.D. Power expects U.S. sales to finish at 12.6 million vehicles, which would be a 9percent increase from 2010. For 2012, it anticipates sales of 14.1 million vehicles, but said a high level of uncertainty remains.