Existing-condo sales in the Miami metro area shot up 58% in September from a year ago, according to a report Thursday from the Miami Association of Realtors. Statewide, condo sales increased 10% year-over-year, with the median sales price up 7% to $87,200. The average sales price in Miami-Dade County went up 13% from $187,185 in September 2010 to $211,455 last month. Existing single-family sales also rose in Florida. However, the rate of sales for new developer-owned condos in downtown Miami slowed last month by 33%, according to CondoVultures.com. About 2,000 of the 22,000 condo units built downtown since 2003 remain unsold, with another 1,000 units bought in bulk sales now being marketed for resale, according to CondoVultures. At the current sales rate, the downtown condo inventory could be gone by the second quarter of 2013. About 4,600 developer units were unsold in September 2010 and about 8,000 were on the market in September 2009. Write to Andrew Scoggin.