There are many impacts encompassed in tropical systems, but storm surge is the most deadly. 50% of deaths attributed to tropical cyclones are caused by storm surge- or the abnormal rise of water above ground and above the predicted tide.
In advance of Dorian, storm surge warnings are in effect for coastal areas with the reasonable worst case scenario calling for 4-7′ of inundation at the most flood prone areas within the warning. An important distinction to know is that number, and storm surge in general, DOES NOT include the predicted tide. It is above that, which unfortunately is forecast to be very high both Wednesday afternoon and especially Thursday morning.
High tides in Charleston harbor at 1 PM Wednesday will reach 1 foot above major flood stage, and roughly 1 AM Thursday even higher at 10.3′ (over two feet above major flood stage). This is roughly comparable (potentially higher) to Matthew’s high tide of 9.3′ or Irma with 9.9′ but below the record high tide associated with Hugo of 12.5′.
The storm surge, caused primarily by the strong winds pushing water onshore when the storm arrives in shallower water, will be on top of that so if you are in areas that often flood- it will flood again Wednesday into Thursday.
Storm surge’s impact is not limited to the coast, it can and will penetrate inland with lessened impact further up tidal rivers and creeks.
Storm surge is complex and influenced by a number of factors: the pressure, intensity, size, and speed of the storm, along with the angle it approaches the coast. The coast itself also dictates the intensity of the surge as well with the shape and local features such as barrier islands and inlets influencing the intensity of the surge.
The bottom line is that storm surge will occur in Dorian- so fully understand what it entails and don’t be surprised by the rising water.