Yesterday (Tuesday) got to 88F at Seattle and today should be very similar. There is one more day of the hot stuff (tomorrow could hit 90F) and then the marine air will move in for cooler temps on Friday and the weekend.
Lets talk about some subleties of the heat. An essential ingredient is the thermal trough (see sea level pressure forecast at 2 PM). If you look closely you will see a tongue of lower pressure extending into western Washington. Also note the low-level winds..they are from the east. Easterly wind bring warm continental air into the lowlands as well as warming due to sinking along the western Cascade slopes.
The profiler gives winds and temperature above Seattle (see graphic). You see easterly flow aloft and near the surface early in the day. Mid-day,northwesterlies and northerlies come in..that is the Sound breeze, essentially a large region sea breeze. Without the Sound breeze, we would be much warmer...like Portland...so you can look at it as our natural air conditioning. By 9 PM the Sound breeze weakens. That is why you should do your kite flying early in the evening...wait too long and the wind dies.
One of the most interesting things the last few days has been the clouds and rain to our south over Oregon and northern CA. The satellite picture below show the clouds over these regions. The origin? A low center off the California coast that has remained quasi-stationary. An interesting aspect of this pattern is that we have been warmer than much of California (see plot of max temps). The whole pattern should shift late tomorrow...with the thermal trough jumping into eastern WA and marine air starting to move in Friday AM.