Hi Ted:
Native Floridian here. I've lived through a few hurricanes. But even I had to have the craziest part of hurricane storm surge explained to me by a meteorologist.
You probably saw several accounts of Sarasota bay and Tampa Bay "emptying out" today. Anyone can look at the counterclockwise rotation of hurricane winds imposed over a map, and see how the water from the NORTH side of the storm was pushed by the wind, around the storm, and then deposited on the land areas on the SOUTH side of the storm, i.e. the Ft. Myers area.
But that's not all there is to storm surge. There is a most interesting phenomenon associated with hurricanes:
Inside the eye, the barometric pressure is the lowest. The water rises up inside the eye as the hurricane approaches the coast.
Depending upon several variables, the water inside the eye of a Cat 4 can be as much as 30 feet higher than the water outside the eye (before the eye hits a land mass).
So when the eye of a storm passes over land, it brings the "higher eye water" along with it.
Once the eye breaches land, the eye wall begins to break down because the eye no longer has water beneath it (this is simplifying things, but I don't need to discuss all the physics). The "higher eye water" starts to "leak" out.
I was watching an unmanned camera on Sanibel Island today that was mounted high up on the second floor balcony of a condo.
When the camera became submerged, I knew then that the eye wall had hit Sanibel.
And you are correct that once the water is released from within the eye, it will naturally "level out." Like when you spill a glass of liquid on your countertop, it moves immediately to the lowest edge and runs on to the floor.
This "higher water inside the eye" is the reason why tide gauges can measure a storm surge of 13 feet in one location, yet a gauge location only, say, ten miles north of the first one, measures just 4 feet of storm surge.
Both gauges are accurate. The northern gauge wasn't located in a place where the eye passed over it, or the eye wall had already started to break down by then.
This is why Sanibel can be hit with a 20 ft storm surge, but Cape Coral may only experience a 5 ft storm surge minutes later.
This is why barrier islands like Sanibel act as "barriers" to storm surge. (In fact, it's why they are called "barrier islands.") A hurricane's eye begins to break down when it passes over a barrier island, and the water contained within the eye starts to "leak out."
There are several other factors that can contribute to storm surge, such as the shallower water close to the coast, but you get the idea.
Photos from Sanibel Island when the sun comes up will certainly be interesting.
Warm Regards,
Mrs. Trombley
Here are a couple of photos of boats aground in hurricane holes on Tampa Bay that I found on the twitter: