The simple way of thinking of this is rolling a ball across a smooth floor versus thick shag carpeting. A low-friction surface will keep the ball moving faster and farther versus the same ball moving at the same force onto a carpeted floor.
Once Florence comes ashore, a rise in land elevation, foliage, buildings, and other protrusions cause friction on the bottom of the hurricane. This will cause a turn to the left and a slowing of its forward progression.
This is bad news when it comes to storm surge (the wall of water that will come ashore). Storm surge will be maximized as the storm decreases in forward speed. In addition, epic amounts of rain are expected. For comparison, Hurricane Hugo from 1989 came in and didn't decrease in forward speed. This one could stall out, bringing two to three feet of rain to the Carolinas into the weekend.
-Meteorologist Eric Sorensen
