(Bloomberg News) Hurricane Irene has the potential to cause serious damage to New York City buildings as it threatens to bring strong winds and surging floodwaters, property managers said as they prepared for the storm's onslaught this weekend.

Irene could be "a once-in-a-lifetime event if it goes according to the forecast," said Jim Rosenbluth, managing director for crisis management at real estate services firm Cushman & Wakefield Inc. Basements and lower levels of buildings close to the shore "would absolutely be at risk," he said.

New York's Building Owners and Managers Association issued a checklist to landlords yesterday urging them to prepare for Irene as Governor Andrew Cuomo declared a state of emergency. Mayor Michael Bloomberg said he is considering evacuations in areas including Brooklyn's Coney Island, lower Manhattan's Battery Park City and parts of Staten Island. He is founder and majority owner of Bloomberg News parent Bloomberg LP.

Irene, now a Category 2 storm, poses the biggest threat to the U.S. Northeast since Hurricane Gloria in 1985. The storm may strengthen later today to a Category 3 hurricane on the five- step Saffir-Simpson scale as it churns toward the North Carolina coast, the U.S. National Hurricane Center said in an advisory at 5 a.m. Miami time.

The center's forecast track shows the storm will make landfall in North Carolina's Outer Banks tomorrow, skirt the East Coast and reach New England on Aug. 28.

Lower Manhattan

The biggest threat to New York buildings may be in lower Manhattan, which would be particularly prone to flooding if it creates a storm surge that pushes through the Verrazano Narrows, said Frank Edwards, executive managing director for project management in the metropolitan New York office of Colliers International, another commercial-property firm. That would cause flooding along the Brooklyn shores as well, he said.

At lower Manhattan's World Trade Center site, where 1 World Trade Center is under construction and workers are racing to finish the Sept. 11 memorial plaza by the 10th anniversary of the attack, contractors were ordered to tie down loose debris, cover electrical equipment, store tools and secure netting. Crews also were preparing to use pumps and sandbags to control flooding, according to a statement by the Port Authority of New York and New Jersey, which owns the 16-acre (6.5-hectare) site.

Landlord Recommendations

The Building Owners and Managers Association recommended in its checklist yesterday that landlords fasten or remove all loose material; secure roof-mounted equipment such as flashings, roof vents and cooling units; secure on-site cranes against high winds; and clean out all drains and catch basins. It also suggested they set up Twitter accounts and Facebook pages for emergency information.

Rosenbluth said he was up at 5 a.m. yesterday checking the latest storm data and computer models. He made a series of calls to Cushman property managers up and down the East Coast to help them prepare to deal with both the hurricane and its aftermath.

Cushman manages 1,127 commercial properties totaling 186.9 million square feet (17.4 million square meters) on the East Coast, according to Adam Leibowitz, an associate with Cushman's corporate occupiers and investor services division.

Category 2

If the storm tracks closely to the west of the city, New York could suffer historic levels of damage at a Category 2 or higher, Rosenbluth said. That would bring winds of at least 96 miles (154 kilometers) per hour, according to the Saffir-Simpson Hurricane Scale.

A nor'easter in December 1992 with wind gusts of up to 77 mph sent the East River gushing over FDR Drive, according to news accounts. Flooding of basements and lower floors of skyscrapers along Water Street downtown prompted some landlords to install flood gates to steer water away from their properties, Edwards said. Those gates may get their first tests if New York gets the worst of the storm, he said.

"I'm sure they're running through their exercises right now, familiarizing themselves with what they need to do to get through this," Edwards said.

A sustained loss of power could put computer data at risk unless backup generators and emergency power supplies are in order, according to Rosenbluth. Wiring, conduits and cabling may be flooded, he said.

Testing Systems

Property management teams are out testing their buildings' safety systems, and marshaling "critical service vendors" such as heating and cooling servicers, landscapers and dewatering services, so they can go to work as soon as it's safe, he said.

Winds from the storm may be especially dangerous in clusters of skyscrapers, Rosenbluth said.

"The narrow canyon effect in an area that's basically vertically developed can create very unique wind patterns where the wind speeds can substantially exceed that which the storm has created -- essentially a channeling or funneling effect," he said.

People should stay off the streets during those periods to avoid flying glass or other debris, Rosenbluth said. The buildings themselves are designed to withstand high winds, he said.