Doctors say it appears the baby was born within 24 hours of being discovered.
He was taken to JFK Medical Center in Edison where he is listed in good condition.
The baby is described as a white male, 7 pounds 8 ounces, and is 21 inches long.
A nursing home visitor apparently noticed the baby on the car, and picked it up and brought it inside CareOne at the Highlands care center and called police.
The baby boy was naked and lying on a towel spread out over the hood of the car as it snowed outside.
He is being held for observation at the hospital, and has been placed in the custody of the New Jersey Division of Youth and Family Services, while police search for relatives.
Anyone with information about the baby is asked to call Detective Al Sciarrillo of the Edison Police Department at (732) 248-7561, or Investigator Daniel Ruschak of the Middlesex County Prosecutor's Office at (732) 745-3600.