A canceled date because of rain is a soft no. New York has too many indoor hours built into it for weather to be a real reason. The trick is to plan the kind of date that benefits from the rain instead of fighting it.
Spend three hours at the Met, properly
The Met is the obvious rainy-day move and people still do it badly. Do not try to see the whole museum. Pick two wings before you go. The Astor Court in the Asian galleries is one of the best quiet rooms in Manhattan and almost nobody is in there on a wet Tuesday. The American Wing courtyard with the Tiffany windows is good for sitting. The rooftop is closed in the cold months but the European paintings on the second floor are always there.
Admission is suggested at 30 dollars for non-residents and pay-what-you-wish for New York State residents and New Jersey and Connecticut students with ID. Bring a small bag because the coat check line is slow when it rains.
End at the cafe in the Petrie Court. It overlooks Central Park through the glass and is the right kind of overpriced.
The Strand, slowly
The Strand at Broadway and 12th is a date in itself if you know how to do it. Go to the third floor first, the rare book room, even if you are not buying anything. Then come back down to fiction on the ground floor. The game is to each pick a book for the other person within twenty minutes, under fifteen dollars, and explain why. You learn more about someone in a bookstore than in most bars.
Across the street, McNally Jackson has a smaller second location on Fulton if you are downtown, and Three Lives on West 10th is the move if you are already in the Village. None of these are 90-minute stops on a sunny day. On a rainy one they are exactly right.
A long lunch at a place with a view of the weather
Rain is a reason to sit somewhere with a window for two hours. Cafe Mogador on St. Marks has the kind of front windows that fog up in the right way. Jack's Wife Freda on Lafayette is good for a long late lunch because they do not rush you. Cafe Sabarsky inside the Neue Galerie at 86th and Fifth is the upgrade move, with Viennese coffee and Klimts upstairs if you want to extend the afternoon.
Sit, order slowly, get a second coffee. The rain does the work.
A movie at a real theater
Streaming has made the movie date feel lazy. A real theater, in the rain, is the opposite. Film Forum on West Houston runs repertory programming and the seats are tight enough that you have an excuse. The Angelika on Houston and Mercer is fine but loud because of the subway. The Paris Theater near the Plaza, owned by Netflix, is the most beautiful single-screen room in the city. Metrograph on Ludlow has a good upstairs bar before and after and is the best option if you want the movie to be part of a longer night.
Get there fifteen minutes early. The pre-movie sit is part of the date.
Tea or a drink at a hotel bar
The hotel bar is invented for rainy weather. Bemelmans at the Carlyle on East 76th is the famous one and worth it once. The bar at the Beekman downtown is quieter and the lobby is the room. The Lobby Bar at the Bowery Hotel has fireplaces in the cold months and is full of people who are also waiting out the weather. Tea at the Plaza Palm Court is a tourist move but if neither of you is from here it works.
One drink, two if it is going well. The point is the room.
A cooking class or a workshop
If you want a rainy date that gives you something to do with your hands, the Brooklyn Kitchen in Industry City runs evening classes and they fill up fast on weekends. The 18th Street pottery studios in Gowanus take drop-ins. The Ukrainian Museum on East 6th has occasional pysanky workshops in spring.
The rain makes these feel deliberate instead of dorky. Use it.
What not to do
Do not plan a rainy date that requires more than two outdoor transitions. Do not pick a rooftop bar and assume the covered section will be open. Do not promise a walk in the park and then improvise when it starts coming down. Pick one indoor anchor and one backup within four blocks. That is the whole strategy.