5 December 2012
When a storm looms in a hurricane-prone area, coastal residents want to know its strength. Will it be a monster Category 5? A meager Category 1? One research team is taking a low-tech approach to try to give people better advance warning.
As anyone living along the East Coast last October knows, hurricane categories can be misleading. Superstorm Sandy qualified as a Category 1, but submerged some regions with coastal surges upwards of 11 feet, well within the range more typical of Category 3 storms.
Hurricane categories are not good indicators of storm surge because the categories are based entirely on windspeed. While windspeed does, indeed, affect storm surge, other factors like storm size, the shape of the coast, and water depth do as well.
Hal Needham, a research associate in the Department of Geography and Anthropology at Louisiana State University, Baton Rouge, realizes that this often confuses coastal residents and is working to better inform people by creating a stand-alone storm surge scale.
To start, Needham’s team is producing the most comprehensive database of storm surge data ever compiled. Focusing on the U.S. Gulf Coast, they scoured thousands of pages of newspapers, government documents, and academic reports to create a list of 230 storm surge events dating as far back 1880, all from real-life observations rather than models.
“The easy part was reading 3,000 pages of newspaper. The hard part was tracking those pages down,” said Needham, joking that a middle school student probably could have done the work, but that it took thousands of hours.
Having plotted all of his surge-height data points on a map, Needham has teased out patterns along the Gulf Coast. In the November 30 International Journal of Climatology, he shows that the region between New Orleans and the east coast of Mississippi has consistently received the region’s highest surges, largely because of the coast’s angular shape—it bends almost at a 90-degree angle, forcing water to funnel to shore.
Needham presented these findings at a poster session Monday afternoon at the 2012 AGU Fall Meeting, emphasizing that such ground-based data can greatly help improve surge prediction models. He also noted that new data, recently submitted for publication, should even further refine such models.
“Surge models tend to look at how strong winds are when the storm hits the coast,” he said. “But that is the wrong question to ask.”
Instead, he explained, his data shows that modelers should look at windspeed in the storm roughly 18 hours before it hits land, since swells take time to form and start building many kilometers out at sea.
Needham’s team is currently working to extend their database, called SURGEDAT, to the East Coast, and eventually to the rest of the world, in an effort to clear up Category 1 confusions and help coastal residents better prepare for the next big storm.
-Laura Poppick is a science communication graduate student at UC Santa Cruz