WASHINGTON (AP) — U.S. home prices rose more slowly in September than in August, a sign that weaker sales are preventing the kinds of sharp price gains that occurred earlier this year. The Standard & Poor's/Case-Shiller 20-city home price index rose 0.7 percent from August to September, down from a 1.3 percent gain from July to August. Year over year, prices jumped 13.3 percent from September 2012, the fastest such gain since February 2006. Monthly price gains slowed in 19 of the 20 cities tracked by the index. Charlotte, N.C., was only city to post a price decline from August to September. The Case-Shiller index covers roughly half of U.S. homes. It isn't adjusted for seasonal variations, so the monthly changes partly reflect slower buying activity in the late summer and fall.