Manhattan’s supply of new-development condominium units remained well below historical norms in the third quarter, according to data from Brown Harris Stevens Development Marketing. The firm put the borough’s “real supply” of condos at 28 percent below its 10-year average.

The measure combines units formally listed for sale with so-called shadow inventory — new-development homes that are not being marketed on the open market. That approach provides a broader view of available and potential inventory than public listings alone.

Analysts at Brown Harris Stevens Development Marketing expect the supply imbalance to deepen in the fourth quarter, according to a report by Commercial Observer. The outlook points to continued constraints in Manhattan’s new-construction condominium market.

For developers, brokers and prospective buyers, the findings underscore the limited volume of new condo stock relative to the borough’s longer-term market baseline. The report also highlights the significance of inventory that remains outside conventional public marketing channels.