Office vacancy rose and rents fell in downtown Seattle and Bellevue as well as in the suburban Eastside market in the third quarter, according to a Cushman & Wakefield report released Wednesday.

Downtown Seattle vacancy climbed to 18.5 percent, a nearly four percentage point increase over the second quarter. The jump reflects downsizing by tenants, vacant space at the former WaMu Center, and the addition of the Fifth & Yesler and 2201 Westlake office projects to the market, the firm said.

“I don’t think this is a surprise to anyone,” said Matt Christian, a Cushman & Wakefield senior director. “We forecasted this increase in the vacancy rate a year ago. We knew this was coming. We knew for awhile the WaMu space (in the former WaMu Center) was coming up. We’ve all been watching these new buildings going up with no tenants, so obviously there’s no surprises here.”

Christian said his firm expects vacancy in downtown Seattle to top out at roughly 21 percent in the first quarter of 2010 and a slow recovery from there.

Russell Investments, whose parent company Northwestern Mutual recently purchased the former WaMu Center downtown, is leasing about 300,000 square feet in that building, Christian said.

JPMorgan Chase is renting about 60,000 square feet, and another 500,000 to 600,000 square feet in the building is being marketed, he said.

In downtown Bellevue, office vacancy rose to 14.8 percent in the third quarter, a 2.1 percentage point jump, driven largely by tenants who downsized or moved outside the market, Cushman & Wakefield said.

In the suburban Eastside, office vacancy increased to 16.5 percent, a 1.2 percentage point rise.

Rents for premium office space in the three markets continued a steady decline that began in fourth quarter of last year for downtown Seattle and Bellevue, and early this year for the Eastside.

The average asking rent for Class A space was $31.90 per square foot in downtown Seattle at the end of the third quarter and $35.25 in downtown Bellevue, Cushman & Wakefield said. That’s a nearly $7 a foot drop in the Emerald City and a $4.23 decline in Bellevue from the fourth quarter of 2008.

The average asking rent for Class A Eastside suburban office space was $32.62 per square foot at the end of the third quarter, a $2.18 a foot decline from the first quarter of this year.

Vacancy rates for Eastside, Northend and Kent Valley industrial space rose in the third quarter, landing at 12.4 percent, 9.2 percent and 9 percent, respectively. That’s about a half percentage point jump for each of those markets over the second quarter, a consequence of the slowdown in the economy, Cushman & Wakefield reported.