Most of Manhattan has fairly good elevation except for the Wall Street
area. I worked on Wall Street for many years and saw a few floods
along the way. The subways are amazingly resilient once power is
restored and things get pumped out. Fresh water comes down from the
Catskill Mountains north of the city and is quite resistent to
contamination on Wall St.
The hurricane of 1938 was similar to the scenario you are describing.
It came into eastern LIS as a Cat 3 and did enormous damage throughout
Long Island and southern New England. The storm surge in NYC knocked
out power and subways, flooded a bunch of sub-basements, etc, but
things were running again in fairly short order. Not true further
east however; places like Block Island still have very few large trees
as a result of that storm, and many coastal towns have hurricane
barriers and gates as a result. There are pictures in the lobby of
Edgartown Yacht Club on Martha's Vineyard that show incredible
devastation to the town and harbor.
I am just going on what I have heard. They say New York is more
vulnerable than it was in 1938 and the hurricane could be more of a
direct hit.
You would certainly have a very low evacuation rate so there could be
10 million people trapped in the city.
Watch it, if you disagree with Plume, you'll be called names and
insulted! Remind you of anybody else here? That's right, I taught her
well.