Forecasting the Surge 



By Kathy Hart 



In the hours before Hurricane Fran landed, Lian Xie 

 sat at his computer at N.C. State University, his fingers 

 flying over the keys as he entered the latest storm 

 information from the National Weather Service into a 

 complicated computer model. 



After 30 minutes of data entry, Xie typed in a 

 command sequence that started his computer thinking, 

 meshing storm statistics with information about the 

 topography of coastal North Carolina. 



The result was a colorful visual representation of 

 likely flood levels on a computer-generated map of 

 Albemarle and Pamlico sounds. 



It didn't look good. Much of the southern Albemarle 

 peninsula was cloaked in yellow, orange and red, 

 representing flood and storm surge heights of 6 to 9 feet. 



With a few more keystrokes, Xie, a researcher in 

 NCSU's Department of Marine, Earth and Atmospheric 

 Sciences, retrieved a time-lapsed, visual sequence of 

 eastern North Carolina flood levels for two-hour 

 intervals during the next 12 hours. The time-lapsed 

 sequence was based on the hurricane's projected path. 



As soon as the information was available, Xie 

 picked up the phone to dial the National Weather 

 Service, conveniently located on NCSU's Centennial 

 Campus. The meteorologists used the information to 

 issue flood warnings for coastal North Carolina. (With 

 the cost of evacuation estimated at $1 million per mile, 

 forecasters like to be as accurate as possible when they 



relay information to the state and local officials who 

 make evacuation decisions.) 



As hurricanes can be, Fran was fickle, and initial 

 data from the National Hurricane Center did not forecast 

 a direct hit for North Carolina's coast. Not to be caught 

 unprepared, Xie ran the model based on a direct hit. 

 When it became apparent Fran was barreling into the Tar 

 Heel coast, Xie had his predictions ready. 



The model, which was partially developed with 

 North Carolina Sea Grant funding, is only as good as the 

 data Xie receives from the National Weather Service. 

 That's why Xie often runs the model for a worst-case 

 scenario. 



And for the most part, his model passed the test 

 with remarkable accuracy. The model predicted an 8- 

 foot storm surge in New Bern. The surge was 9 feet. 



Although Xie's model only predicts soundside 

 flooding, other models developed at Princeton Univer- 

 sity and by the National Hurricane Center forecast 

 oceanside surges. Xie is developing a new computer 

 model that will integrate ocean, sound and coastal river 

 surge and flood predictions. He hopes it will be opera- 

 tional before the next hurricane strikes. 



Meanwhile, meteorologists at the National Weather 

 Center and officials at the state Division of Emergency 

 Management are happy to have the information Xie can 

 generate now. The predictions make their jobs easier and 

 their forecasts more accurate, possibly saving the lives 

 of coastal residents. EI 



1960s, the code required that all buildings use stronger 

 connectors, such as metal straps securing the roof to the 

 walls, to resist wind damage and that they be raised on 

 pilings. Buildings were required to be elevated above the 

 historical high watermark, but in most cases, contractors 

 boosted them even higher to allow underhouse parking and 

 storage. 



In erosion-prone areas, it was also necessary to sink the 

 pilings 8 feet into the ground to keep the building stable and 

 prevent damage if storm waters scoured away sand. 



"These building code regulations changed the public's 

 perception of what a beach house looks like in North 

 Carolina," Rogers says. "It came to be expected that all 

 beach houses be elevated on pilings with underhouse 

 parking. That's what people think of when we say beach 

 house now." 



For the most part, houses built to meet these code 

 requirements fared well if they weren't beachfront or 

 second-row structures, Rogers says. 



On the oceanfront, pilings sunk 8 feet into the sand 

 weren't deep enough. The waves swept the sand from under 

 these houses, leaving no support for the pilings. Houses 

 toppled off their foundations, disintegrating in the waves or 

 knocking into other homes as they floated landward. 



In 1986, on Roger's advice, the N.C. Building Code 

 Council enacted new rules for erosion-prone areas that 

 required pilings be sunk 5 feet below sea level or 16 feet 

 below ground level. 



Most of the houses built since then, including those on 

 the oceanfront, sustained the least damage in Hurricane Fran. 



"There was an overwhelming reduction in the level of 

 damage in these houses, Rogers says. 



"We're not so overconfident to think that we have all the 

 answers regarding hurricane-resistant construction," he says. 

 "We're still looking in detail at how buildings fared. But I'm 

 certainly pleased that newer buildings performed so much 

 better, and I think we are much closer to building hurricane- 

 resistant houses on the coast than ever before." □ 



COASTWATCH 7 



