I live in Boston and it was a balmy 28 degrees farenheit yesterday. I leave in 9 days but had I left yesterday, I would wear jeans, T-shirt, long sleeve shirt, hoodie sweatshirt and suffer being a little cold for a short time.
In my carry on, I would have a change of warm weather clothes and room to put my current clothing in. But would most likely just change my jeans for shorts and take off the long sleeve t-shirt and hoodie.
Leave the bag in the car, at bell services, or in a locker.
I just painted a picture of someone calmly adjusting to the conditions. But the picture really will look like some running down the beach to the water scrambling to get their clothes off before they hit the water in a big splash.