WASHINGTON—Sales of new U.S. single-family homes surged to a six-month high in September, but higher house price are making homeownership less affordable for some first-time buyers. New home sales jumped 14.0 percent to a seasonally adjusted annual rate of 800,000 units last month, the highest level since March, the Commerce Department said on Tuesday. August’s sales pace was revised down to 702,000 units from the previously reported 740,000 units. Sales increased in the populous South, as well as in the West and Northeast. They, however, fell in the Midwest. Economists polled by Reuters had forecast new home sales, which account for more than 10 percent of U.S. home sales, increasing to a rate of 760,000 units. Sales dropped 17.6 percent on a year-on-year basis in September. They peaked at a rate of 993,000 units in January, which was the highest since the end of 2006. Demand for housing surged early …