TAMPA - The U.S. housing market may be turning a corner, and Bay area home prices continue to show signs of improvement, according a report released Tuesday.

The Standard & Poor's/Case-Shiller's U.S. National Home Price Index shows national home prices posted the first quarterly increase in three years. Prices rose nearly 3 percent in the second quarter compared with the first quarter, though prices are still down almost 15 percent from a year ago.

The Tampa metro area saw prices increase a slight 0.4 percent from May to June. That follows no change in prices from April to May and may indicate prices are starting to stabilize. Still, prices are down 19.5 percent compared with 2008.

"The Tampa area was severely affected by the downturn," said Maureen Maitland, a vice president with S&P. "It's showing improvement but not the same positive signs as some other cities."

The index tracks 20 major cities. The national index, a composite of home price indexes for the nine U.S. Census Bureau divisions, is compiled quarterly.

It will take many more months of consecutive increases to point to a turnaround, Maitland said. The national index is encouraging, she said, but it's still unclear what the data really show.

"Is this a temporary pause because of the spring buying season and buying incentives, or is it the beginning of a turning point?" Maitland said. "There's a mixture of variables such as unemployment that could change the data."

Every metro area shows annual declines, with 15 reporting double-digit drops. Miami, the only other Florida city tracked, posted a 23.4 percent yearly decline in June and a 0.5 percent increase from May to June.

Las Vegas and Detroit were the only two cities with monthly declines. Dallas and Denver posted increases for the fourth month in a row.

Reporter Shannon Behnken can be reached at (813) 259-7804.