Jason Beisel, a spokesman for the Florida city of Clearwater, described the scene in a tweet on Sunday: "Creepy site - water in Tampa Bay is already being sucked out. This is view from downtown St. Pete waterfront."
In Charlotte Harbor, the second largest bay in Florida, Dylan Branscome posted a video on Facebook showing dry, sandy landscape as if the bay had evaporated.
In places like Tampa and Port Charlotte, as the storm approaches from the south, strong winds blowing from the northeast have pushed water out of shallow parts of bays and harbors, according to CNN meteorologist Judson Jones.
"As soon as the wind shifts direction, the water will come back quickly and continue to move inland," Jones said.
"The height of the storm surge will depend on the exact track of the storm. If the eye of the storm tracks to the west of the bays, the storm surge will be worse."
'Gee whiz' element
Shuyi Chen, a professor of atmospheric sciences at the University of Washington in Seattle, said the weather phenomena is common during extreme storm conditions like Hurricane Sandy in 2012.
"After the storm center passes Tampa, the wind will change from offshore to onshore and push water and large ocean surface waves onshore," he said, referring to the storm surge.
"In addition to onshore wind, Irma's northward motion will bring extreme large surface waves when it gets closer to Tampa."
A storm surge
is a gradual rise in the water level caused by a major storm's wind as it gets closer to shore.
Chen said the strength, size and forward motion of the hurricane affect ocean surface waves, water level and temperature -- effectively changing the shape of the ocean.
Scott Hagen, director of the Center for Coastal Resiliency at Louisiana State University, said there is a "gee whiz" element to the phenomena.
"It's such a rarity along the west coast of Florida," he said. "I had expected it but to see it must really be dramatic if you actually get to go out there and take a look at it."
Therein lies the danger.
"Don't get caught up in that," Hagen said.
"There's a sense of awe. Just like when we're frightened. When we see something that we haven't seen before and we're so amazed by it, we take chances that we really shouldn't be taking."
He added, "It is within the realm of possibility that (the water) comes back more dramatically than if it were just a surge blowing up on land without the water being removed from the shore areas by the winds ahead of the eye of the storm."
The receding shoreline can give people a false sense of security, CNN meteorologist Gene Norman said.
"It is particularly dangerous because it may not be apparent that the winds have switched to an onshore direction," he said. "Similar to those who come out during the passing of the eye. Winds will and do pick up again once the eye passes."
'Move away from the water!'
Indeed, on Sunday afternoon, the National Hurricane Center tweeted:
"Urgent warning about the rapid rise of water on the SW FL coast with the passage of #Irma's eye. MOVE AWAY FROM THE WATER!"
The tweet was accompanied with this note of caution:
"With the passage of the eye of Irma during the next couple of hours, the wind direction will shift to onshore, causing water levels along the southwest coast of Florida to rapidly rise in a matter of minutes. MOVE AWAY FROM THE WATER! Life-threatening storm surge inundation of 10 to 15 feet above ground level is expected in this area."