Part of my family comes from the Maritime Provinces of Canada. Although their summers don’t get quite so hot as the Mid-Atlantic region, still there’s plenty of water available to saturate the air at ant temp - making the relative humidity feel the same. But, they rarely have sticky days. Why? Maybe I overlooked something in my thinking…
I WAG it’s really high pressure off the Gulf of Mexico that makes the Mid Atlantic so sticky, as opposed to the local waterways? If so, that’s not fair ofr Mother Nature to let the Gulf’s influence extend so far! 
- Jinx