33 Minutes

A little bit of searching will let you find out that Iran has practiced launching ballistic missiles from container ships, and coincidentally practiced using trajectories that would be optimal for an EMP weapon.

Personally, I think we're more likely to see a full-blown nuke or a dirty bomb exploded dockside in a container port. Long Beach would be my guess, but Seattle or Tacoma would be high on the list as well. Downtown ports in both cases. West Coast ports rather than East Coast to maximize fallout contamination across the countryside.

If you're not worried, you're not paying attention.