The number of real estate contracts signed and recorded declined 5.6% from August to September, as home affordability receded under the influence of higher mortgage rates, home prices and consumer uncertainty, the National Association of Realtors concluded Monday.

The NAR Pending Home Sales Index – a barometer of real estate contract signings – fell from an index score of 107.6 in August to 101.6 in September. It also declined 1.2% from year ago levels when the index hovered at 102.8.

This is the lowest index level reached since December of last year, and NAR is blaming the influence of declining home affordability, lower consumer confidence and a government shutdown that shook up both construction activity and home sales.

"Declining housing affordability conditions are likely responsible for the bulk of reduced contract activity," said Lawrence Yun, NAR’s chief economist. "In addition, government and contract workers were on the sidelines with growing insecurity over lawmakers’ inability to agree on a budget. A broader hit on consumer confidence from general uncertainty also curbs major expenditures such as home purchases."

The numbers suggest a lackluster fourth quarter, with Yun saying for the first time in 29 months pending home sales failed to come in above year ago levels.

"This tells us to expect lower home sales for the fourth quarter, with a flat trend going into 2014," he said. "Even so, ongoing inventory shortages will continue to lift home prices, though at a slower single-digit growth rate next year."

Regionally, the pending home sales index fell the most in the Northeast, declining 9.6% to an index score of 76.7. The Midwest index declined 8.3% to 102.3, but remained 5.7% above year ago levels. The South also saw sales slip 0.4% to an index score of 116.2 even though the index is still 2% above year ago levels.

The West sales index fell 9% in September to an index score of 97.3, also down 9.8% from a year earlier.

However, 2013 was a solid year for home sales overall. Numbers recorded in the first part of the year will make 2013 a high performing 12-month period overall.

NAR says total existing-home sales will end up 10% higher when compared to 2012 levels, with 5.1 million sales expected. This could even hold heading into 2014, the latest NAR report says.

Meanwhile, the national median existing-home price is expected to rise 11% to 11.5% for all of 2013, while experiencing a moderate 5% to 6% gain next year.