Existing home sales continued a downward trend in September, according to the National Association of Realtors. The organization said ongoing affordability concerns—driven by rising home prices, higher mortgage rates, and insufficient inventory—are keeping many would-be buyers from entering the market.

The seasonally adjusted rate for annual sales of existing single-family homes, condominiums, co-ops, and townhomes stood at 5.15 million. This was down 3.4 percent from August and 4.1 percent from September 2017, making it the seventh consecutive month of year-over-year declines in sales.

"This is the lowest existing home sales level since November 2015," said Lawrence Yun, chief economist at the National Association of Realtors. "A decade's high mortgage rates are preventing consumers from making quick decisions on home purchases. All the while, affordable home listings remain low, continuing to spur underperforming sales activity across the country."

The median price for an existing home rose for the 79th straight month, reaching $258,100 in September. This marked a year-over-year increase of 4.2 percent.

Single-family homes, which accounted for the bulk of existing home sales, had a median sales price of $260,500 – up 4.6 percent from the previous year. The seasonally adjusted annual sales rate for this type of property was 4.58 million, a drop of 3.4 percent from August and 4 percent from September 2017.

The annual sales rate for condominium and co-op sales fell 3.4 percent from the previous month and 5 percent from the previous year to 570,000. The median price for a condominium or co-op sold in September climbed 1.5 percent to $239,200.

A total of 1.88 million existing homes were listed for sale in September, down from 1.91 million in August. However, this was a slight increase from 1.86 million listings in September 2017.

The average commitment rate for a 30-year fixed rate mortgage stood at 4.63 percent, up from 4.55 percent in August. This was also more than half a point higher than the average rate of 3.99 percent for 2017 as a whole.

The typical existing home sold in September stayed on the market for 32 days, three days slower than in August but two days faster than in September 2017. Forty-seven percent of homes sold in September found a buyer within a month of being listed.

"There is a clear shift in the market with another month of rising inventory on a year-over-year basis, though seasonal factors are leading to a third straight month of declining inventory," said Yun. "Homes will take a bit longer to sell compared to the superheated fast pace seen earlier this year."

Twenty-one percent of existing homes sold in September were made without financing, up from 20 percent in both August and September 2017. Individual investors, who typically account for such all-cash sales, made up 13 percent of the month's purchases – unchanged from the previous month and down from 15 percent in September 2017.

First-time buyers were slightly more prevalent, with their share of the month's purchases increasing from 29 percent in September 2017 and 31 percent in August to 32 percent. However, this still lagged below the annual share of 34 percent identified in the National Association of Realtors' latest Profile of Home Buyers and Sellers, released in late 2017.

"Despite small month-over-month increases, the share of first-time buyers in the market continues to underwhelm because there are simply not enough listings in their price range," said Elizabeth Mendenhall, president of the National Association of Realtors. "Entry-level homes remain highly sought after, as prospective buyers are advised to contact a Realtor as early in the buying process as possible in order to ensure buyers can act fast on listings that catch their eye."

Distressed sales held at a record low of 3 percent of all transactions, the lowest since the National Association of Realtors began tracking this information in October 2008. This share was unchanged from August and down from 4 percent in September 2017.

In regional breakdowns, the sharpest decline in existing home sales occurred in the West. The region's annual sales rate of 1.08 million was down 3.6 percent from the previous month and 12.2 percent from the previous year. The median price for an existing home sold in the West was $388,500, a year-over-year increase of 4.1 percent.

The annual rate of 680,000 existing home sales in the Northeast marked a drop of 2.9 percent from August and 5.6 percent from September 2017. The median sales price in the region was up 4.1 percent to $286,200.

In the Midwest, the annual rate of 1.28 million existing home sales was unchanged from the previous month but down 1.5 percent from the previous year. The median sales price of $200,200 was up 1.9 percent from September 2017.

The sales rate in the South fell 5.4 percent from August and 0.5 percent from September 2017 to 2.11 million. The median price for an existing home in the region rose 3 percent to $223,900.