Get a rear fender if you can. Either one of the backscratcher types or a Race blade. Helps keep the shammy dry even when the rest of you is wet. At the very least apply some packing or duct tape underneath if you have a cutout saddle.
The skin cooling is a biggie - extra calories help so make sure you got plenty of snacks. 75 is warm in the dry, but in the wet with the added windchill of being on the bike, prep like it's 60. Also 75 might be the high of the day which may not hit until late morning.
An Assos rain cap, or any type of rain cap. It's easier to hold onto body heat if that does become a factor.
Drop your tires 5-7psi. Will add some traction.
I also like to use my taillight when it's raining. If it's bright out doesn't really help, but when overcast and stormy it does help a bit more than nothing.
Eyewear helps if you're doing any paceline riding. Many big parks in NYC have horse riding. This is probably a non-issue for you but when I race in the rain I try to keep my mouth closed when we ride through the crossing areas
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One of my favorite things is riding in warm rain. Hope you have a great ride.