A national improvement in home foreclosure rates hasn't seeped into the Tampa Bay area, according to California-based ForeclosureS.com. While national preforeclosure filings dipped 7.5 percent from March to April, the number of such mortgage defaults continued to rise locally. Pinellas, Pasco, Hillsborough and Hernando counties tallied 21,474 preforeclosure filings through April 30. Based on the percentage of households afflicted with mortgages in default, Pinellas comes off the best and Hernando the worst, suggesting problem home loans become more severe the farther you move into the newer suburbs. Florida has had 162,316 preforeclosure filings so far this year, which amounted to 2.56 percent of all households. More homes entered the foreclosure pipeline in Miami-Dade County alone than in the four-county Tampa Bay area combined.