Thrice or more apparently. Blogger NYCisMyMuse posts on YouTube:

I caught three direct strikes to the Empire State Building lightning rod after midnight on 4/13/11 during a severe thunderstorm. I actually saw a fourth direct hit, but sadly wasn’t filming at the time. I’ve never seen so many hits on the ESB in one night. It was ridiculous! But so much fun to watch.

Whoever said lightning doesn’t strike twice was wrong.