Snall, harmless appearing container ship.
Greek or Panamanian registry.
Papers all in order for Port Newark–Elizabeth Marine Terminal,
Ship manned by English speaking Norks and non-english speaking Africans, etc.
Detonated about 20 miles offshore
The tidal wave would bury Manhattan
AT 20 miles away (and this is considering a MT weapon) by the time it got to Manhattan it would just be a normal storm surge type event.