The short answer is: “dress in layers” and bring a jacket and hat. Generally at 3 or 4 PM in the afternoon the temperature is near the peak of the day. So if you dress comfortably when you leave house you will only be adding layers. It will be seem cooler when you are more exposed the wind as is the case when you are on the water. On a windy day 60 degrees can seem down right cold. That’s when adding a windbreaker, perhaps with a sweater or fleece under makes all the difference. So bring them along, even a blanket to wrap around your legs is a good idea. (We have blankets onboard)
Fortunately, Now & Zen has a canvas and plastic enclosure so you can duck out of the wind but still enjoy the view. That said, one of the greatest places on a catamaran is to spread out on the bow trampolines and if it is cool or breezy you’ll want add those layers you brought along especially that hat with a chin strap.