(Bloomberg) -- When a hurricane comes ashore, there are so manydangers: tree-snapping winds, torrential downpours and eventornadoes spawned by the tempest itself.

But it’s the wall of water that tropical systems push onto land,known as storm surge, that tops the list.

“Storm surge has historically taken the most lives,” Rick Knabb,director of the National Hurricane Center, said by telephoneyesterday.

For the estimated 22 million Americans living in hurricane-pronecoastal areas the question is: Am I at risk?

A new online tool released by the hurricane center this weekshould provide some of the answers.

Overlays showing water heights from hurricanes of varying powerare projected on a U.S. map that users can scroll down into to showstreet-by-street detail.

Hurricanes come in different sizes and follow unique paths, sothe tool isn’t a prediction of exactly what will happen if aCategory 3 storm hits Southampton, Long Island.

It does show that people living there may want to consider theiroptions. The same is true for people in any of the other placesthat face the Atlantic and Gulf of Mexico.

The maps also show neighborhoods that are behind levees, whichcan be vulnerable, as New Orleans was in Katrina, if they shouldbreak because of a storm.

“It is a valuable tool for showing who is at risk and who needsto be putting together a personal or family or business plan forevacuation,” Knabb said. “I hope the big result is that peoplerealize they are vulnerable to storm surge and that they puttogether a plan now.”

Insurance Coverage

As recent years bear out, there is no region that is safe from astrike. The last hurricane to hit Florida was Wilma in 2005,Knabb said. Since then, the Northeast has been hit by Irene andSandy as well as a number of near misses.

People in the Northeast may be more aware of storms in recentyears than those living in Florida and along the Gulfcoast, two areas that have been hit the most since records began in1851.

Eight storms have formed during this year’s Atlantic season,which runs from June 1 to Nov. 30. The 30-year average calls for 12storms with winds of at least 39 miles (63 kilometers) perhour.

Evacuation Calls

Regardless of what the map indicates, Knabb stressed that peopleneed to heed evacuation calls. Emergency managers take a lot morethan just storm surge into consideration when they advise people toleave their homes and businesses.

Tropical systems regularly cause deluges of fresh water floodingfar behind where they come ashore, as did Tropical Storm Irene whenit inundated Vermont in 2011.

Sandy dropped three feet of snow, closing roads and knocking outpower, throughout the Appalachians in 2012. Hurricanes and tropicalstorms touch off tornadoes, collapse buildings and can hurl debristhrough the air like missiles.

Danger comes in a lot of different forms in a hurricane.

The biggest of them is now measurable on your desktop.

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