WASHINGTON — The October surprise goes by the name Sandy.

And unlike many late-breaking developments of U.S. presidential elections past, neither side is certain which candidate, if either, will be helped or hurt.

What's clear for both President Obama and his Republican challenger Mitt Romney is that the superstorm brewing off the East Coast is shaking up an already hard-to-predict contest as it enters its pivotal final week, upending campaign schedules and interfering with the rivals' ability to communicate with voters as they make their closing arguments.