What Brooklyn and Janet and LisaP said -- in my (limited) personal experience, it's not the heat, it's the humidity! Or, at least, it's not only the heat. Humidity plays a huge role in how hot you feel and how covered (or not) you want to be.
For much of my life I lived in southern (and then, later, eastern) Ontario. You might think "cold" when you think Canada, and you'd be right. But southern Ontario summers can be almost as steamy as Baltimore's. They are just shorter overall...and there are usually breaks between the really hot spells -- a few cooler days. Temperatures might read in the 30s (high 80s for you) but the humidity can be high.
In weather like that, I am 100% with you -- a "summer" outfit (typically, in southern Ontario, mid-June to mid-September) is breezy, cotton or linen, without sleeves (if possible), without added layers, sometimes without jewellery because it just sticks to the skin!
Or, at least, that's how I need to dress if there is no arctic AC. Air conditioning makes it a lot more complicated. Yes, I'll carry a topper, but there's still a risk of frozen toes in sandals. Ugh.
In Ontario, I barely ever needed clothes that I might call "transitional" -- i.e. sleeved lightweight tops, closed summery shoes. As Jules said -- it was sandals or boots.
I now live in the Pacific Northwest. Here, the climate is completely different. Summer is still June-mid-September. Except... May can be surprisingly warm, in the high teens or 20sC (70s). And June can be weirdly cool -- as low as 13C. (55 F). So I I do need more covered yet lightweight items and I might need to wear them on any day of the year. I'll favour them in different colours during different seasons, though.
The light is summer light, and the air is different. So that's a factor in how I want to dress as well.
