Temperature of 90 F and RH of 80% is a dewpoint of of about 83 F.
That is a rare extreme actually for anywhere in the USA.
Weather.com publishes a dewpoint map, and the highest I ever saw on that map was 82 F, for the worst of the heatwave of July 12-15 1995. I have looked at that map hundreds of times, mostly at times of the year when the numbers on that map are higher.
I tried web searching for extremely high dewpoints in the USA, and as it turns out 86 F dewpoint does rarely turn up for localized areas in late morning in a severe heatwave in an agricultural area favoring humidity (Iowa cornfield or a steamy spot in Georgia).
I suspect you are remembering the RH from breakfast time and not realizing that it drops when the temperature goes up as the day goes on.
The worst dewpoint recorded in Chicago was 83 degrees F - I think that was on July 12 or 13 or so 1995.
The worst dewpoint I know Philadelphia to have been befallen with was at 4 PM July 15 1995. (Unusually late in the day in a heatwave - dewpoint on a heatwave day usually peaks in late morning or close to noon.) 102 F, 54% RH, dewpoint 82 F. The heat index was 129 F. - Don Klipstein ( snipped-for-privacy@misty.com)