One World Trade Center already is New York's tallest building.

Freedom Tower at One World Trade Center (Laurie Cataldo, Townsquare Media NJ)

And when the last pieces of its spire rise to the roof on Monday — weather permitting — the 104-floor skyscraper will be feet from becoming the highest in the Western Hemisphere.

The Port Authority of New York and New Jersey says the spire pieces plus a steel beacon will then be lifted at a later date from the rooftop to cap the building at 1,776 feet.

The new high-rise replaces the twin towers destroyed on Sept. 11, 2001.

The 408-foot spire will serve as a world-class broadcast antenna.

The new tower is at the northwest corner of the World Trade Center site, which is well on its way to reconstruction with the 72-story Four World Trade Center and other buildings.