The view north to Central Park Tower and 111 West 57th Street on Billionaires Row from the 86th-floor observation deck at the Empire State Building on July 28, 2019, in New York City. (Photo by Gary Hershorn/Getty Images)

Real estate sales in Manhattan have fallen eight out of the past nine quarters, according to a report from real estate brokerage firm Douglas Elliman and appraiser Miller Samuel.

The average sales price fell 7.5% to $1.8 million in the fourth quarter of 2019 and the median sales price fell below $1 million. Total sales were down, discounts were up and there is now an eight-month supply of unsold apartments.

While many brokers say they're optimistic about a potential turnaround in 2020, real estate experts say they expect a continued — though perhaps slower — decline this year as tax pressures and rising inventory keep buyers on the sidelines.

"I think we'll see more of the same," said Jonathan Miller, CEO of Miller Samuel. "The problem with saying that 2020 will mark the bottom is that it suggests it will go up after that. And I think we still have another couple of years of moving sideways."

The slow bleed in Manhattan real estate comes despite a strong economy and record-high stock market.

A new mansion tax on multimillion-dollar apartments, the new federal cap on state and local tax deductions, which makes high-tax states like New York more expensive, and a lack of foreign buyers has continued to weigh on demand. Add to that an oversupply of luxury apartments, with another 2,000 new condos coming onto the market this year, and buyers are shifting rapidly to the rental market, especially on the high end.

Sales of apartments priced at $5 million or more plunged 38% in the quarter and there is now a two-year supply of luxury apartments on the market. Beyond the official inventory, brokers say there is a mountain of "shadow inventory" — or apartments that aren't officially listed but are waiting for market conditions to improve and sales to clear before they list.

According to Halstead Development Marketing, there is a now a six-year supply of new development apartments. The biggest glut is on "Billionaire's Row" — the string of super-towers along 57th Street, where there is more than $9 billion in shadow inventory waiting to list.

Halstead said the dollar value of closings in the fourth quarter was down 27% from last year.