Tampa, Florida, has avoided a direct hit by a major hurricane since 1921. That luck appears likely to end on Sunday, and it may do so in disastrous fashion.
Tampa-St. Petersburg is a rapidly-growing, low-lying metropolitan area of nearly 3 million, with a coastline that is highly vulnerable to storm surge flooding from a tropical storm or hurricane. If the forecast track of Hurricane Irma verifies, and the storm’s center passes just to the west of the city, then onshore winds will pile up water into Tampa Bay.
This could lead to a reasonable worst case scenario of having 6 feet or more of surge inundation in homes, businesses, and critical infrastructure such as parts of MacDill Air Force Base, where U.S. military operations in the Middle East are overseen, according to maps from the National Hurricane Center.
We know we are ground zero for this storm. We have avoided it for 90 years but our time has come to be ready.
— Bob Buckhorn (@BobBuckhorn) September 10, 2017
Scientists and journalists have warned for years that Tampa is a sitting duck for a storm surge disaster. On CNN Saturday night, Tampa Mayor Bob Buckhorn cited the city’s lack of a direct hit by a Category 3 or greater storm since 1921, when he said: “It looks like our day has come.”
That 1921 storm brought a storm surge of 10.5 feet to Tampa, which was mostly undeveloped land at the time.
In 2015, the risk consultancy Karen Clark and Company published a report ranking Tampa/St Petersburg as the most at-risk city in the U.S., with potential losses of $175 billion from what it termed a 100-year storm. The storm the report based its calculations on was slightly stronger than Hurricane Irma is forecast to be when it nears Tampa.
The report found that the shallow continental shelf off the west coast of Florida allows a major rise in water with a landfalling hurricane, and that Tampa Bay “creates a large funnel,” pushing water toward the shore.
“A severe storm with the right track orientation will cause an enormous buildup of water that will become trapped in the bay and inundate large areas of Tampa and St. Petersburg,” the report found. “Fifty percent of the population lives on ground elevations less than ten feet.”
As of Sunday morning, the Hurricane Center was predicting 5 to 8 feet of storm surge flooding above normally dry ground if the peak surge hits at high tide. A larger surge is predicted just south of there, including Sarasota, Bradenton, Ft. Myers, and Naples, where a potentially devastating 10 to 15 feet of water above ground level is predicted.
Inundation forecast maps for Naples and Ft. Myers show large portions of these areas underwater in a worst-case scenario. A storm surge of 6 to 10 feet is forecast for Sarasota and Bradenton, which could also produce widespread damage there.
Before the flooding occurs, the offshore flow ahead of the storm is causing the tides to recede from the beaches in Ft. Myers, Naples, and other areas. However, that water will rise rapidly once the center of the storm passes.
The flooding in these areas will depend on the angle at which the storm approaches the coast. Because it is moving parallel to the coast, from south to north, any small wobble of the eye — which typically occurs in such storms — could mean a big difference in where Irma makes its second landfall in the U.S. mainland.