This search tells me a bunch of New York's major TV stations (channels 2, 7, 11, 13, 31 & 47) are moving from the Empire State Building to the World Trade Center spire. Their height will go up, and their power down. Of those now I only get channel 2 (which actually transmits on channel 33) in my apartment at the other end of Manhattan, which is shadowed from the transmitter by many blocks of taller buildings. I'm sure to lose it after it moves even farther away, with a weaker signal.
I also notice that channels 11 and 13 have directional signals, which are the rated power in only one or two directions, and weaker elsewhere. Also that channel 7 for some reason is far more powerful than the other VHF (7-13) channels, even though it's the same power, using the same master antenna, back on the Empire State Building.
Of course all of these are just place-holders. Almost nobody watches TV from an antenna any more. They're watching on cable, satellite or over the Net.
And over-the-air is probably doomed anyway, since the FCC has incentivized station owners to relinquish their spectrum rights in a very tempting auction. Here's more from The Verge.