youngbeginner, BTW I just found this article about extreme heat and humidity in the northeast US on 7/19/2013. Notice how moderate the RHs are compared to your claims:
Hottest day: Humidity reaches obscene range, heat breaks records
By
Jason Samenow,
Published: July 19 at 11:12 amE-mail the writer
The summer’s longest, most extreme heat wave extends to its fifth day, cooking the Great Lakes, Mid-Atlantic and Northeast. For Washington, D.C., under an
excessive heat warning, today may well be the most brutal, with heat indices approaching 110 degrees.
141 million people under heat advisories and warnings
USA Today
reports 23 states and 141 million people are under advisories and warnings. The most intense heat and humidity coincides with the I-95 corridor from Richmond to Boston.
Heat advisories shaded in orange, excessive heat warnings in magenta. (National Weather Service)
From Richmond to New York City, the humidity levels are particularly unbearable, with dew points in the upper 70s to around 80 degrees
Dew points at 11 a.m. (National Weather Service)