Hurricane Ian increased to a Category 2 storm on Monday with 100 mph winds.
Forecasters expect the storm to increase to a Category 3 as it heads towards Florida.
A Category 5 storm would be devastating and produce a 26-foot flood.
As Hurricane Ian intensifies and heads toward the Florida Gulf Coast, forecasters are sounding the alarm for what could become a Category 3 storm with 111 mph winds.
"This is a near worst-case approach angle coming in from the south and west and stalling," Jamie Rhome, the National Hurricane Center acting director, told CNN. "With it slowing down, this would be a near-worst case approach angle."
The last time a storm that strong hit Florida was a century ago, when a Category 3 came to Tampa Bay, knocking out the region's power and killing eight people. But that was when the population was only about 200,000, according to Tampa Bay Times.
Tampa Bay, which includes the cities of Tampa, St. Petersburg, and Clearwater, is now home to about 3.2 million people, according to the 2020 US Census. In a worst-case scenario - a Category 5 with winds of 157 mph or higher - the impacts could be devastating and take years to recover from.
As a storm pushes water towards Tampa Bay, the region can expect a 26-foot flood, which is more than twice the depth of the 1921 hurricane, according to Vox.
In the Tampa Bay Regional Planning Council's catastrophic plan, which lays out this exact worst-case scenario through a simulation called Hurricane Phoenix, the flooding would turn various parts of Pinellas County, including St. Petersburg, into islands.
In addition, winds of up 157 mph would tear through homes, smash windows, and destroy stoplights. About half a million buildings could be destroyed and 843,000 households displaced, according to the catastrophic plan.
The death toll would reach similar figures to that of Hurricane Katrina in 2005, when the Category 5 storm killed over 1,800 people, according to Vox. The region's planning council estimated that - even considering Tampa Bay's developed infrastructure - a storm that strong could kill about 2,000 people, along with another 200 more after the storm.
Economic losses also would be unprecedented. The report estimates about $250 billion in "expected economic losses" due to structural damages and loss of business.
"As one might expect, a storm of the size and strength of Hurricane Phoenix would create almost unthinkable damage to the area's homes, businesses, infrastructure, overall economy, and social systems that are currently in place," the report stated.