Hurricane Milton's storm surge could be a major problem for Tampa Bay

Tampa Bay – the nation's most vulnerable metro area to storm surge – could be about to see its worst flooding in over a century if some of the more dire forecasts for the path of Hurricane Milton hold true.

With a forecast of 8 to 12 feet of seawater flooding the Tampa Bay area, it's the "highest storm surge forecast ever explicitly issued by the National Hurricane Center for Tampa Bay," according to Michael Lowry, a hurricane specialist at WPLG Local 10 in Miami.

Evacuations already have begun in the Tampa metro area, which is home to about 3.5 million people, as the storm approached, mainly because of the storm surge threat. "Storm surge is historically the single deadliest hazard of a hurricane, responsible for more than half of all hurricane-related deaths over the past 50 years, and is the primary reason evacuations are issued ahead of hurricanes," Lowry said.

More: Hurricane Milton tracker: Follow projected path of storm expected to hit Florida

Nation's most vulnerable city

A 2015 report by Karen Clark & Company, a risk modeling firm, said the Tampa-St. Petersburg metro area was the nation's most vulnerable to the threat of storm surge.

The report said a Category 4 storm striking just north of Tampa Bay could be expected to cause $230 billion in damage just from the storm surge, as noted by meteorologist Jeff Masters on the Yale Climate Connections blog.

Unable to view our graphics? Click here to see them. 

Why is Tampa so vulnerable to storm surge?

There are several reasons why Tampa is the most vulnerable U.S. city to storm surge, according to the 2015 report:

First, the continental shelf is relatively wide off the west coast of Florida. That large expanse of shallow continental shelf waters offshore from Tampa Bay (less than 300 feet deep out to 90 miles offshore) helps allow large storm surges to build, Masters said. That accentuates the rise in sea surface from a major hurricane.

Second, Tampa Bay creates a large funnel ? particularly for a hurricane with its radius of maximum winds near the mouth of the bay, the report said.

More: Powerful Hurricane Milton hits Category 5 status on path to Florida: Live updates

"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. Fifty percent of the population lives on ground elevations less than 10 feet.

1921 hurricane remains the benchmark

Tampa has not had a direct hit by a major hurricane since 1921. That storm was barely a Category 3, the report said.

According to Yale Climate Connections, the Tampa Bay hurricane of Oct. 25, 1921, was the last major hurricane to make landfall in the Tampa Bay region. "This low-end Category 3 storm with 115 mph winds at landfall brought a storm tide of 10-11.5 feet, causing severe damage ($180 million 2024 dollars.)"

In 2004, Hurricane Charley was headed toward Tampa, but just before landfall it made an unexpected turn to the south, the Karen Clark report said.

Forecast errors

Milton’s track is crucial to where the worst of its storm surge pushes ashore, Lowry said. As of Monday afternoon, much of the west coast of Florida was in the hurricane center's "cone of uncertainty," including the entire Tampa Bay metro area.

But the current forecast track is far from etched in stone.

Unfortunately, the average forecast error even 12 to 24 hours before landfall is 20 to 40 miles. Florida’s oblique peninsula magnifies these typical errors, which makes it impossible to know exactly where the worst storm surge will strike, Lowry said.

This article originally appeared on USA TODAY: Hurricane Milton storm surge could bring historic floods to Tampa Bay