Have you seen the now viral video of bare land where ocean used to be in the Bahamas and Tampa Bay?
There is a scientific explanation for this...What happened in that video - and what is currently happening along the west coast of Florida is a result of persistent wind blowing the water away from the coastline. Think of it as the opposite of a typical storm surge. Instead of piling up the water against the coast, it's pushing it back out to sea.
This phenomenon is maximized when you have shallow water (bays, inlets, etc.) and a low tide. These areas are especially susceptible. Because Irma is producing consistent offshore winds in certain places, water is pushed out toward the ocean instead of toward the coast. That creates the eerie photos you've probably seen of "dry" coastlines.
But don't be fooled! Once the winds shift direction or die down, the water will come back up! This is a particularly dangerous situation because the water levels could actually turn into a traditional storm surge if the winds switch direction by 180° and drive the water back toward the coast. Though there is an explanation for all of this, it is still a rare phenomenon to see!