It’s all about the wind.
That’s why we’re seeing the footage of extreme low tides associated with Hurricane Irma. The same thing happened in Alabama’s Mobile Bay during Hurricane Katrina. In fact, the same thing happens here and in most other parts of the Gulf coast on a regular basis.
Strong winds, such as those associated with Irma, can override the effect of the tide. It doesn’t take much. In Mobile Bay, a stout north wind of 25 miles per hour or so for two days in a row will cause a similar effect, though not as extreme. We see it every winter. The longer the wind keeps up, the lower the water level gets. In some bitter cold winters, such as those in the early 2000s, when the north wind blew for days and days, water receded close to 1,000 feet from the normal shoreline, four to five feet below normal.
With the hurricane, what we are seeing has to do with which side of the storm various places are seeing. Because a hurricanes winds blow in a circular pattern, the winds in each quadrant of the storm are coming from a different direction. For Tampa and cities on the west coast of Florida, their initial exposure to the storm is coming from the Northeast. That’s perfect to push water out of Tampa Bay.
As the winds change, that water will come rushing back in. I’ve seen a storm surge rise and the fall. It was an awesome sight.
During Hurricane Katrina, the news crew stayed in the Press-Register’s newsroom. We had a ringside seat to watch Katrina’s water rise from our glass-windowed, third floor newsroom on the edge of the Mobile-Tensaw Delta. Amusingly, the newspaper’s address was on Water Street. The name proved prescient during the storm, as Mobile Bay rose up and surrounded us. The newspaper, built at 15 feet above sea level, was rendered an island unto itself.
Early in the storm, I remember driving out to look at Mobile Bay and seeing gigantic mud flats where the water had retreated in the early part of the storm, when winds were from the north at 50 miles an hour.
Then, as the storm moved over us, the surge came in. As it crept down six lane Water Street, standing waves developed from the current. The water rose 15 feet in two hours, or about an inch and a half per minute. It was a stunning sight. The road was rendered a rushing river. All was still for a moment, as the eye passed. Then, as we pushed through the back of the eye wall, the water rushed away as quickly as it had come.
The surge is magnified in coastal bays, where the water is forced into a giant funnel as the bay’s narrow. The newsroom and downtown Mobile were at the head of the funnel when you look at a map of Mobile Bay. Tampa is similarly positioned on its bay.
For a moment, imagine the storm surge of Katrina in Biloxi. 28 feet. That is a tsunami-size wall of water. As happened in Mississippi, all that water that rushed out along the Florida coast, is rushing back in right now. The surge is usually the most dangerous part of any storm.
I hope for the best for those folks we saw on all the news networks out on the dry bay bottom. They are definitely in harm’s way tonight. Godspeed.