Matthew Toys With Florida Coast; Major Surge Threat Remains
After barreling across the Caribbean and through the Bahamas, Hurricane Matthew backed off from an immediate U.S. landfall on Thursday night, and odds were rising that the system might not come fully ashore before looping out to sea over the weekend....At 2:00 am EDT Friday, NHC downgraded Matthew to a Category 3 storm, with top sustained winds of 120 mph...
Hurricane-force winds are possible as far north as coastal Georgia and southern South Carolina later on Friday, but the primary threat here will be high water--the most deadly aspect of U.S. hurricanes. Because of the gradual expansion of Matthew’s wind field, its direction of motion, and the largely concave geometry of the coastline, barrier islands and inlets from north FL to southern SC remain at risk of major storm surge even if Matthew remains offshore. Late Thursday night, NHC was projecting the potential for coastal inundations of 7 to 11 feet from Sebastian Inlet, Florida, to Edisto Beach, South Carolina, including parts of the St. Johns River between the coast and Jacksonville. Breaking waves of up to 20 - 25 feet are possible atop the coastal surge.
Time and again in recent years, we’ve seen hurricanes weaken in terms of peak winds as they approach the coast, yet push far more water onshore than residents expected. This is one reason why the Saffir-Simpson scale no longer directly relates its strength categories to storm surge: peak winds near the center are an unreliable index to how much surge a hurricane may actually produce. Even if Matthew weakens and stays offshore as projected, surge levels in some areas (especially far north Florida and Georgia) may be the highest observed in many decades, and I fear that many coastal residents will underestimate this risk