It's definitely a confusing time. I do what Janet does and transition little by little. I'm about to put the sandals away today except for one pair of sandal booties that might get an outing or two if it gets warm during the days. My shorts can probably go away now also, and most of my short-sleeved tees. But I'll keep the longer sleeved linen tees for a few weeks yet. Bit by bit.
It also helps a lot to dress in layers, I find. So in the weather you're describing I might have worn cropped jeans, sandals or sandal booties, a sleeveless top, and a light topper of some kind (to be removed in the heat).