Waves beat the seawall on Asharoken Avenue as superstorm Sandy...

Waves beat the seawall on Asharoken Avenue as superstorm Sandy nears Long Island. (Oct. 29, 2012) Credit: Peter Walden Sr.

Sandy's storm surge flooded Long Island at historic levels that exceeded benchmark storms from the 1990s and rivaled the great hurricane of 1938, according to data collected by the federal government.

The superstorm's surge was equal to a Category 2 hurricane's, scientists and the United States Geological Survey said.

"We haven't recorded anything as high as the surge we've seen from Sandy," said Ronald Busciolano, USGS supervisory hydrologist in Coram. "In the western part of Long Island, we've never seen anything like this."

The 1938 hurricane, known as the Long Island Express, produced storm tides of 14 to 18 feet across parts of the Island, said Scott Mandia, a professor of physical sciences at Suffolk County Community College, and author of a book about the hurricane.

The peak storm surge during Sandy occurred at Long Beach, where the surge reached 17.48 feet, according to the USGS.

"For folks that felt the full brunt of it, in New Jersey, New York, Long Island and Long Island Sound, the surge was significant enough to qualify it as historic," said Jamie Rhome, a storm surge specialist with NOAA's National Hurricane Center in Miami.

Storm surge is the height of the water that is above the normal tide level. When the normal astronomical tide level is added to the storm surge, the resulting calculation is called the storm tide.

Flooding exceeded the Federal Emergency Management Agency's 100-year base for flood elevations, a measurement the disaster-relief agency uses to create flood maps for insurance purposes, the USGS said.

The flood maps are based on the surge estimated to be created by a storm of the severity expected once every 100 years.

"We're doing an evaluation of the entire region that was hit by Sandy," said Tim Crowley, mitigation director for FEMA's Region II, which includes New York. "We anticipate that, by mid-month, the results will be out."

Mandia said that another storm like Sandy might require FEMA to revise its predictive maps because intense storms, fueled by rising sea levels, could occur more frequently.

"The 100-year flood -- that no longer applies," Mandia said. "These storms aren't once-in-100-year events. They're probably once every 25 years."


Higher water than in '91, '92, '11

Peak storm tides from Sandy surpassed high-water marks from the Halloween eve storm in 1991, the December 1992 storm and from Tropical Storm Irene in 2011, according to the USGS.

Record storm surge levels on the South Shore of Nassau County peaked between 8 and 9 feet, preliminary USGS data show.

Record coastal flooding also occurred in the western Great South Bay in southern Suffolk County. The peak storm surge surpassed high-water marks from the 1991 and 1992 storms, when the surge topped 6 feet. Farther east, the highest storm surges reached between 7 and 9 feet, the USGS said.

At one spot along the North Shore of Nassau County, the peak storm surge during superstorm Sandy was recorded at 12 feet, 6 inches less than the previous record from the Dec. 11, 1992, storm, government data show.

Storm surge from Sandy caused flooding in thousands of homes on Long Island and the storm left nearly 1 million LIPA customers without power. It also claimed 13 lives. More than $10 billion in economic activity was lost because of Sandy. Gov. Andrew M. Cuomo last week asked Congress for $42 billion to help New York State recover. Of that money, $8.4 billion was to be for reconstruction on Long Island.

The USGS and the National Oceanic and Atmospheric Administration are nearly done putting together a map that shows Long Island's storm surge from Sandy. The map is about 85 to 90 percent complete, according to the USGS.


Crunching the numbers

USGS workers have been loading data collected from its instruments measuring storm surge and calculating barometric pressure into a mapping program, along with making field inspections, since Oct. 29 when Sandy hit the hardest. Data collected on the surge was downloaded to managers of FEMA, which has already used the information to decide where to send help for residents with flooded homes, Busciolano said.

Officials don't expect the USGS map to change significantly once it is completed.

"As a scientist, it's giving us the ability to understand how different areas were impacted," said Aram Terchunian, of First Coastal Corporation of Westhampton Beach, an environmental consulting firm. "Models are models, and data is data."

During the December 1992 nor'easter, the National Weather Service said the storm tides were 8 to 15 feet above normal and exceeded records set during previous damaging nor'easters in 1950 and 1953.

On Oct. 30, 1991, a storm pushed storm tides 5 feet above normal and caused $34 million in damages. The storm reshaped the Island's coastline. Waves were up to 15 feet in some places, swallowed shorelines and cut off beaches from Freeport to Montauk.

FEMA in 2009 revised its flood maps, which provide zones that are likely to flood in a major storm. The map included much larger areas along the South Shore in Nassau.

The proposed changes drew outrage from residents with mortgages who complained that they had no choice but to buy federal flood insurance at much higher prices than in the past.

Residents of neighborhoods in Massapequa Park and Valley Stream who have argued that their homes should never have been designated in a flood-prone area said Sandy's flooding did not reach their homes.

A meeting was scheduled before the storm in Valley Stream to update residents on revising the map. That session will now be delayed. With Bill Bleyer

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