Scientist warns about effects of storm surges

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It’s no secret that the East End is prone to dangerous flooding during hurricanes and nor’easters, but determining just how much flooding can be expected during storms remains an imprecise science.

Dr. Brian Colle, a meteorologist who works for Stony Brook University’s School of Marine and Atmospheric Sciences, has been working to narrow down the variables that contribute to storm surges. He gave a lecture explaining his findings at Stony Brook Southampton last month.

Storm surges are the total water level minus the effects that tide has on how much water comes ashore during storms, but they’ve historically been difficult to determine thanks to the lack of scientific knowledge about underwater terrain.

Dr. Colle’s model is one of many that university research groups have created that runs simulations of water patterns using a complex formula based on the temperature, pressure, wind conditions, underwater features and other factors that can drastically change the prediction of how much water will come ashore. His research is focused on all of Long Island and New York City.

The National Weather Service is able to integrate his model with its own data and that of other researchers to present an ever-more accurate prediction of how much water will come ashore during major storms and where that water will be. All that data, though, is dependent on the exact nature of the storm.

“In a Category 3 hurricane, the water could go into Sunrise Highway,” said Dr. Colle. “The 1938 hurricane created Shinnecock Inlet.”

Dr. Colle estimated that a Category 3 hurricane, like one in 1821 that created an 18-foot-high storm surge at the Battery in New York City, would cover Manhattan with water as far north as Canal Street.

“In the 21st century, we’ve yet to have one. We’re actually overdue,” he said of such a storm.

It is not just hurricanes that fall under the research group’s concern. Nor’easters can cause more flood damage if they are sustained over a long period of time, due in part to the fact that they usually last through several tide cycles. Nor’easters also lack the circular nature of hurricanes, exposing vulnerable shorelines to floods pushed ashore by sustained winds out of the same direction.

Dr. Colle’s data is not specific enough to micromanage an evacuation effort, but ultimately, he hopes, the simulations will be used to help manage disasters here.

“We can’t pinpoint exactly which streets to evacuate and I don’t think we will anytime soon,” he said. “But we can change the bathymetry, add barriers. We can show a breach of Fire Island and the barrier beaches and how biology changes as a result of the shift. There’s a lot of power in these simulations.”

Among the factors that make his work so difficult are the differing wavescapes on the ocean, which can dramatically alter the way water enters the bays and coves on the East End. During some storms, the ocean is covered with lumpy swells. During others, the waves are choppy and disorganized. The storm surges associated with different wavescapes can vary to a great degree.

“The waves pull the water toward the beach,” he said, adding that his group is working on coupling a wave model with the surge model to improve its accuracy. He said that there is also “huge uncertainty” about the forces at work between the air and the sea that may lead to a much greater or lower storm surge.

The limits of the models are directly tied to the limits in computer processing speed, he said. Currently, his group runs about eight simulations per day on a cluster of LINUX-based computers, but each new variable slows the speed of computing to a degree that it can become too slow for forecasters looking for up-to-the minute data.

Dr. Colle said the best way to counteract the inability of his group to assimilate all the available data is to engage in “ensemble forecasts” with other research universities. All the groups send their data to the National Weather Service, which compiles a graph of the mean of all of their statistics, which very closely mirrors the actual storm surges that were predicted.

Dr. Colle said the group can run a simulation and send it to the National Weather Service on very short notice in the event of a disastrous storm.

The problem with testing the model in real-time, however, is that Long Island has seen very few major flood-producing storms in recent years. Dr. Colle doubts that pattern will last, though he said that Long Island could not be entirely evacuated if the worst case storm were to appear on the horizon.

“You can’t get everyone over the bridges in three days,” he said, adding that the storm water from a Category 3 hurricane would cover the entrance to the Brooklyn Battery Tunnel. The best thing to do, he said, would be to seek shelter on high ground in the center of the island.

As he stood on the podium in Chancellor’s Hall, a stone’s throw from Shinnecock Bay, Dr. Colle was asked by a member of the audience how best to prepare for a Category 1 storm in Southampton.

“Don’t stick around to see how high the water gets,” he said.

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