The highest storm surges in Tampa Bay are usually associated with hurricanes, with the three highest tides occurring during Cat 3 storms in 1848, 1921 and 1985.
Hurricane Elena in late August of 1985 caused the highest storm surge recorded at the St. Petersburg tide gauge which has been in operation since Dec. 1946. Late on the 31st of August the gauge recorded a water level some 4.0 feet above Mean Higher High Water (MHHW) or 6.26 feet above Mean Lower Low Water (MLLW) as Hurricane Elena hovered offshore over the Gulf of Mexico.
The day prior, Hurricane Elena was about 200 miles southeast of the mouth of the Mississippi when it turned eastward. During the next 24-36 hours, the storm moved closer to the west coast of Florida but then stalled about 50 miles off Cedar Key. At its closest point to Tampa Bay, late on the evening of the 31st, Elena was packing winds to 100 knots making it a Cat. 3 storm.
Due to the slow and erratic motion of this storm, warnings were issued along the Gulf from Sarasota to Grand Island, LA. All told, 1.5 million people, including about 300,00 in the Tampa Bay area were evacuated. Residents of the Tampa Bay area endured heavy rains and winds, evacuations were ordered and many chose hold-up in shelters. On September 1st, Elena started to move westward again and finally made landfall near Biloxi, Mississippi on Sept. 2nd as a category 3 hurricane.
Prior to the tide gauge being installed at St. Petersburg, there were at least 2 incidences of higher surges. The highest reported storm tide in Tampa Bay occurred in September of 1848 during the “Great Tampa Gale” when the tide was reported to have been 15 feet above low tide or about 12.75 feet above MHHW. During the October Hurricane of 1921 the tide was reported to have reached 10.5 feet above low water or about 8.25 feet above MHHW.
What about the future?
There have been two Cat 3 hurricanes that have directly impacted the Tampa Bay area since 1848 with the last event in October of 1921, nearly 100 years ago. Although these events are rare they can and will happen again. Based on the above, I would estimate that there is a 1-2% risk for a major hurricane impacting the Tampa Bay area in any given year. Hurricane Elena, although it did not directly hit Tampa Bay, created a storm surge that was significant. Even though there has never been a Cat. 5 storm to hit Tampa Bay, it is not impossible and the devastation would be extreme.
A 2010 study called Project Phoenix funded by FEMA took a look at the Tampa Bay area as if we were hit by a Cat 5 hurricane. In this “worst case” scenario, power outages would be widespread with all of Pinellas County being without power with Pasco and Hillsborough Counties experiencing nearly total power outages as well. The associated storm surge would be as high as 26 feet in Tampa, 24 feet in Apollo Beach, and 20 feet in St. Petersburg.
All told, the storm could result in up to 2,000 people dead, 2 million injured, and almost 500,000 homes and businesses destroyed. All three bridges between Tampa Bay and the Courtney Campbell Causeway would “sustain either structural damage or have their approaches washed away by water and waves”