Oh yes, Dianthus are great just about anywhere! They are a really great flowering plant. I just took more cuttings of mine & plan to have them spaced close together for more impact.
Also, I forgot about my favorite–penstemon. There are hundreds of varieties! There are some that are shrubby groundcovers, tall groundcovers, and some that make really great focal points.
For the person who needs something that can take direct sun in the afternoons, there are so many options! Salvias, dianthus, anthemis, rudbeckia, coreopsis, all types of mallows and hollyhocks. The last few can take part sun, even part strong sun, and work beautifully. I think the key is to not overwater when a plant only gets 4 hours of burning sun a day, and it is humid. Some others are: monarda, yarrow, cleome, cosmos, snapdragons, goat’s beard, queen of the prairie, joe pye weed, astrantia, swan plant, verbascum, butterfly weed, baptisia, and lady’s mantle.
Some of those can get quite large, so that may be a factor. Believe it or not, a lot of the perennial poppies can take those kinds of conditions as well, just be sure to not overwater them the 2nd and subsequent years….
Some things I wouldn’t recommend, simply because of your humidity, and it only being part sun are: Veronica (would get floppy the 2nd year), peony (peony blight, cause by not enough sun, too much humidity), Viscarias with blue foliage, phlox (humidity; same thing–creates mold! yuck!), some catmints (may become invasive with those conditions), snow-in-summer, snow-on-the-mountain, iceplant, canna (not enough sun for those last two), and russian sage. Some of those would get too invasive, or simply not thrive in humid, part-sun.
Quite a few annuals would do really great, too. Those listed as part-sun would work. The ones that say full sun would grow, but they might be one single flower the entire summer, as opposed to a full, bushy deal.