These are the average January temperatures since the year 2000:
Caldwell N.J. 30.4
Islip N.Y. 31.5
Newark 32.8
Kennedy 33
Central Park 33.4
LaGuardia 34.1
3 things stick out to me. One, Newark is colder than Central Park, possibly because Central Park daytime highs are higher with no foliage. Two, the heat island affect. You would think Islip would be warmer than Central Park and Newark. Islip has more of an ocean influence but it apparently can't make up for the highly dense urbanization of the more inland areas like Newark and Central Park. Three, LaGuardia is a degree warmer than Kennedy even though Kennedy has more of an ocean influence which in the winter is a milder influence.