U.S. homebuilders are feeling less optimistic about their sales prospects, reflecting concerns that rebuilding efforts following hurricanes Harvey and Irma will drive up costs for construction labor and materials.

Even so, builders' overall view of the new-home market remains positive.

The National Association of Home Builders/Wells Fargo builder sentiment index released Monday slipped to 64 this month. That's down three points from a downwardly revised reading of 67 in August.

Readings above 50 indicate more builders view sales conditions as good rather than poor. The index has been above 60 since September last year.

The latest index fell short of analyst predictions, which called for a reading of 67, according to FactSet.

Readings gauging builders' view of sales now and over the next six months declined from last month. A measure of traffic by prospective buyers also fell.

Sales of new U.S. homes are running ahead of last year's pace, reflecting strong demand for homes as the economy has continued to create jobs. Still, sales posted their biggest one-month drop in nearly a year in July, sliding 9.4 percent to a seasonally adjusted annual rate of 571,000. August new-home sales figures are due out next week.

Sales stumbled this summer as a supply crunch elevated average home prices nationwide. In response, builders are ramping up the supply of new homes, providing a crucial outlet. But the number of newly built properties available is still below historical levels.

While home construction is up about 2.3 percent so far this year, builders say they are hamstrung by shortages of skilled workers and land parcels ready for new construction.

That dearth of skilled construction labor is expected to get worse as the wake of Hurricane Harvey, which plowed through Texas and Louisiana late last month, and Hurricane Irma, which slammed into Florida earlier this month. Rebuilding in the aftermath of the two deadly and devastating storms is expected to drive construction costs higher and cause delays.

"The recent hurricanes have intensified our members' concerns about the availability of labor and the cost of building materials," said NAHB Chairman Granger MacDonald, a homebuilder and developer from Kerrville, Texas. "Once the rebuilding process is underway, I expect builder confidence will return to the high levels we saw this spring."

This month's builder index was based on 328 respondents.

A measure of current sales conditions for single-family homes fell four points to 70, while an outlook for sales over the next six months slid four points to 73. Builders' view of traffic by prospective buyers edged down one point to 47.