COLUMBUS (WCMH)—Hurricane Matthew delivered multiple blows in the southeastern part of the country this weekend—80-100 mph wind gusts; torrential rain falling at a rate of up to 4 inches an hour; huge waves; and coastal flooding that tore up roads and chewed up beachfront homes.
The biggest threat turned out to be water driven by powerful onshore winds that created a record storm surge along the coast of Georgia as high as 12 feet above normal water level. Coupled with high astronomical tide, major flooding ensued as water was forced into inlets that backed up coastal waterways.
Water weighs about 1,700 pounds per cubic yard, capable of massive damage during a powerful storm surge.
For the first time, the National Weather Service issued prototype storm surge warnings, from a few feet to more than nine feet, using increased supercomputer capabilities. The drive to develop better warning for storm surge arose from disasters like Hurricane Katrina in 2005, where the rising ocean was responsible for many direct and indirect deaths amidst the staggering death toll in excess of 1,500 persons. The storm surge reportedly reached 27 feet as Katrina approached the Louisiana coast.
Storm tide takes into account the rise in water level, associated with a strong pressure difference, and astronomical tide that leads to devastating flooding, when the passage of a hurricane coincides with the mean high tide. Water pushed toward land “piles up” as the seafloor bottom rises along the continental shelf.
There are many variables regarding predicting storm surge at any location: the forward speed and intensity of a hurricane, the angle the storm takes relative to the coast, and the size of the radius of maximum winds (RMW). Local topographic features (shape of the coast) also plays a role in the severity of the flooding.