Although some forecast outlets are going for a major cool-down into the 70s from todays 93F....it is looking more and more that it is going to be much warmer tomorrow than expected. At the point I would predict low to mid 80s...and 84F would be a good number for Sea Tac.
Why do I say that? The onshore push tonight will be exceedingly weak...that is evident by the lack of an onshore pressure difference. The clouds moving in overhead will work against nighttime cooling. Computer models only suggest a modest cool down aloft. And the thin stratus deck offshore evaporated this afternoon. There will be very limited low clouds tomorrow am. So plenty of sun through the remnant of the middle level clouds moving through aloft. So don't get rid of your fans yet....in fact, I purchased one tonight myself! (Sales tip...Rite Aid has a sale on fans)
With the middle level clouds, somewhat more humid air, and lack of wind, it really feels like an East Coast summer tonight...yes, not quite as sticky...but it is reminiscent.
Sunday will be a step down, with a far greater chance for morning low clouds. But they will probably burn off by mid-day and temps should climb into the mid-70s.