By Tom Ehrich

A storm like Hurricane Sandy starts by drawing lines. Then it blurs those lines.

Maps showed who was in “Frankenstorm’s” path and who was beyond its destructive reach. New York City braced for the worst.

Later maps showed New Jersey a pending disaster and New York City outside the line of truly-awful. Live reports by the amazing crew of CBS-2 showed 20-foot waves at Atlantic City and calm but steadily advancing water breaching the seawall at Manhattan’s southern tip.

But then we in Manhattan began to understand that slow-moving flood. Soon it would pour into subway tunnels and power equipment – eventually flooding seven tunnels beneath the East River and causing one power plant to explode. Bridges, ferries and all rail service were suspended, turning the heartbeat of the “connected” economy back into an isolated island.

Now, new lines would emerge. Power would be cut off – preemptively, to protect equipment – south of Battery Park, then south of 14th Street, then south of 39th Street, with another potentially ruinous high tide to come this morning.

Residents of Brooklyn and Queens saw their own lines of safe/unsafe, evacuate/stay. Fires destroyed 80-100 homes in an oceanside area of Queens.

As quickly as we took solace in being north of 39th or inland from Far Rockaway, we soon saw air-traffic disruptions that will cascade across the country, closing of stock exchanges that will cascade around the world, mass-transit closings that will disrupt stores and offices, many billions of dollars lost that could cripple some enterprises and drive some people over the line to poverty.

New York works by being the hub of global commerce, global communications and global travel. When New York stops working, shudders spread far and wide.

As the day of Sandy’s arrival proceeded, my wife and I took a walk along the Hudson to marvel at the oncoming flood, then we hunkered down at home. We watched CBS-2 document the storm. I felt humbled by the hundreds of first-responders who were putting out fires and clearing live wires, as well as medical personnel carrying NYU Hospital patients down stairwells and out to ambulances for relocation to other medical centers.

I noticed something. People were praying for us. People in untouched places like Houston and Indianapolis, and in the far-flung world of Facebook were lifting us up to God. Our sons checked in from California and Upstate New York. Friends sent messages.

We weren’t alone, stranded on the wrong side of some line.

My own prayers are following the storm north into New England, where we have family, and where recently-made friends in Vermont suffered mightily from Irene in 2011 and could face more flooding.

As New Yorkers began saying to each other after 9/11, “We’re all in this together.”