Ballots were mailed on October 14.  According to King County Election, the most recent count of  ballots returned as of yesterday, October 21,  is 20,582 or 5.47 percent.

In the Primary, the ballots were mailed on July 29th.  If you take the same number of days, seven, so August 5th, King County Elections said they had processed 11,038 or 2.93 percent.

The County is expecting  57 percent "turnout" for the general in Seattle.  The primary turnout was 38.6 percent in Seattle.

So, while they aren't expecting twice the turnout for the general, the ballots are coming twice as fast so far.