The first thing to note is just how big it is, relative to the width of the Florida peninsula. The width of the track of hurricane-force winds (74 mph at the edges, 185 in the middle) near PR and Cuba can be seen in the NYTimes graphic below. Note that the track width is more than the width of the Florida peninsula, about 140 miles.
The worst place for the hurricane to turn north is where it is predicted to turn. The predicted path takes it straight up the peninsula like a giant eraser. And the damage isn’t just wind and rain. With this path, both sides of the state will experience strong flooding as the winds push water ashore, initially up the Atlantic coast and then once the eye is farther north, the NW winds will start pushing Gulf Coast water ashore on the west side. The offshore depths there can be shallow.
Scientists have been worried about a storm this strong for a decade or more, given the buoy measures of the equatorial band of water stretching from the Cape Verdes off Africa to the Caribbean. It has been getting hotter, largely from our global overheating from fossil fuels, providing more heat to power a hurricane. But no one could have predicted that the monster would turn to take a path straight up Florida as its major landfall.
It could be worse if, say, an equatorial monster first took a circuit around the Gulf of Mexico (where many of the big hurricanes have picked up their power) before landfall.