I wouldn't worry too much about being struck by lightning on a road bike, but I'd be somewhat concerned about the roads being suddenly wet (especially if they haven't been in a while and both you and the drivers have forgotten the experience a bit), driving rain, hail, winds, less visibility, and drivers in a hurry to get home.

I spent the weekend climbing in Leavenworth, in the hot sun. On my way toward Blewett Pass, I went through a summer thunderstorm. It was producing hail the size of quarters. The music on the radio was interrupted twice for the emergency broadcast system, it warned of flash flooding in a particular canyon and urged people "to take immediate precautions to protect life and property." I don't think flash floods are going to be an issue in NY.