Notheast quadrant will be pushing surge into the coast if the eye tracks up the coast. That is the main danger in NE Florida and Georgia, rainfall is the primary danger in the Carolinas. And if Matthew pulls a Charlie and tracks just 15 miles further west than expected, it will be even worse. They simply cannot forecast this track with exact precision, which is why folks need to prepare for worst case.
Chances are it will track a little more to the west. When hurricanes interact with land, friction reduces the wind speed on the landward side. This creates an effect of pulling the storm closer to the coast. Seen it many times. Good news is he main hammer of this storm is in the east side. Doesn’t mean there won’t be destruction, but the worst that this storm has to offer is on the east side which should remain over water. Recon data, specifically the SFMR wind data, shows the west side is only cat 1 strength with cat 2 gusts. Thats good news. Surge will be bad over a large area. Severe wind damage will be confined to the immediate coast and first teir counties. Fresh water flooding will be sporadic. He total impacts will cover a large area just because of the track.