Some have already noticed this fall’s high rate of apartment vacancies in some Boston neighborhoods.

But it’s also a national problem, as the apartment vacancy rate rose in the third quarter to 7.8 percent, the highest since 1986.

The most commonly cited reason: high unemployment. Normally, people flock to rental properties during recessions. But this isn’t your typical recession, with the jobless rate at 9.8 percent nationally (for September) and 9.1 percent in Massachusetts (for August – updated number apparently not available yet).

Experts think vacancy rates will climb higher as we enter the traditionally slower winter rental months.

Rent prices may be lower these days in some Boston neighborhoods. But the Boston-area market still ranks fourth highest in prices after New York, San Francisco and Fairfield County, Conn., for apartment building rentals.