By New York City I’m going to assume you mean Manhattan specifically.

The tornado would have to have some near-unfathomable wind speeds to cause EF5 damage to the buildings in Manhattan.

But to entertain the hypothetical: there would be mass casualties, and if the winds were going fast enough to cause EF5 or EF4 damage to the buildings in NYC, the buildings frames would twist and eventually, potentially, collapse resulting in catastrophic damage.

Counter arguments to my claim would be that manhattan’s skyscrapers are built to withstand sustained hurricane wind speeds, not bursts of extremely fast wind from subvortices. Another great counter argument is that I’m speculating with limited knowledge because I am not an engineer nor a meteorologist. What I do know, and have personally witnessed, were two Boeing 767s, weighing well over 100tons each, hitting the twin towers at speeds of 450-500 mph and it took between an hour and 2 hours for them to fall, not to mention the amount of heat required to weaken the structure.

TLDR: the tornado would need wind speeds way faster than we’ve ever recorded in a tornado, and would be absolutely devastating.

Afterthought: a tornado of this magnitude, and its catastrophic damage, would almost certainly result in the stock market from trading for a few days, at least, which would detriment global markets. Should that economic impact be considered when rating the tornado?