Now people along the coast will be able to gauge where it could happen and how deep it could get. This year, for the first time, National Hurricane Center forecasts will carry a color map as storms approach, showing what areas could be flooded and approximately how deep. The maps will be displayed when the first tropical storm watches go out, then updated every six hours or so as a storm progresses.

The forecasts are experimental, the accuracy uncertain and any prediction made would be subject to the wild variables of each storm.

But the extra heads-up is very valuable, emergency managers agree. Like other aspects of hurricane landfall, surge has been difficult to prepare for, because it's been difficult to predict. Only in the past few years have state emergency managers revamped how evacuations will be ordered based partly on the surge.

Surge is a powerful, flooding coastal overwash from waves pushed higher and stronger by a hurricane. Because of the wiles of tides, wind, sea bottoms and hurricane path, it can be stronger or weaker than the strength of a hurricane would suggest.

At least one-third of the people who live along the South Carolina coast aren't sure if they live in a place that could be flooded by a storm surge, according to a 2012 survey. And when surge washes up, it tends to spread. Unlike other areas in the Atlantic Basin, the waters of the relatively wide Continental Shelf off the Lowcountry are not deep enough to allow surge flooding to easily escape back to sea.

"Storm surge can be completely separate from the category (strength) of the storm. Having that added piece of information helps us make better decisions," said Derrec Becker, S.C. Emergency Management Division public information coordinator.

"As with anything, it will have to be tested in the real world in real hurricanes. (Last) week (of ice and sleet) has shown us that despite the technology, weather is chaotic. We make our plans to be flexible enough to adapt" if forecasts don't pan out, he said. But when it comes to emergency preparations, he said, there's no such thing as too much information.

The map is designed as supplemental information, said James Brinkley, National Oceanic and Atmospheric Administration storm surge operations manager; the modelling has been in development for several years.

"We're very confident" in its accuracy, he said, adding, "weather is always prone to some degree of error."

Modelers at the Lowcountry Hazards Center at the College of Charleston have developed their own storm surge prediction programs, using combined laser and radar to more finely gauge subtleties like elevation, bringing in natural and social science methods to get a finer, community-scale read on values, risks and resilience.

"There's been a lot of discussion" about the accuracy of various storm surge modelling, said Norman Levine, the hazards center director. To get it right requires detailed water depth and surface readings, he said.

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