(Bloomberg) -- Hurricane Milton is building up a potentially disastrous storm surge as it churns toward Florida’s west coast, where flooding and high winds are expected to inflict widespread damage and put lives at risk.

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Milton’s top winds surged to 155 miles (250 kilometers) per hour, after dropping earlier Tuesday, making it a Category 4 hurricane on the five-step Saffir-Simpson scale. While Milton’s winds may fluctuate until landfall, it will still be capable of devastation across the Florida peninsula when it arrives Wednesday night, the US National Hurricane Center said in an advisory at 2 p.m. New York time.

“Today is the last full day for Florida residents to get their families and homes ready and evacuate if told to do so,” Robbie Berg, a meteorologist at the hurricane center, said in his forecast.

Residents have begun to flee the coastline, including the city of Tampa. Florida was set to start free evacuation shuttles in Pinellas, Pasco and Hillsborough counties Tuesday, and social media showed scenes of bumper-to-bumper traffic on highways.

“This is literally catastrophic,” Tampa Mayor Jane Castor said in an interview with CNN. “I can say this without any dramatization whatsoever: If you choose to stay in one of those evacuation areas, you are going to die.”

All United Airlines Holdings Inc. flights out of Tampa, Orlando, Fort Myers and Sarasota are fully booked today through Thursday, the carrier said in a statement. The airline has booked 25,000 customers from those airports, including 2,750 on 18 added flights. It’s also using larger planes on some flights.

About 62% of flights originating at Tampa International Airport have been canceled today, as have 84% of flights scheduled into the airport, according to FlightAware.com. About a third of flights at Southwest Florida International in Fort Myers have been canceled.

Governor Ron DeSantis said roadway tolls have been suspended and shoulders will be used as travel lanes to help people leave.

“Looking at how big this storm is, there’s going to be significant damage in different parts of Florida,” DeSantis said at a news conference.

Milton already forced evacuations across Mexico’s Yucatan Peninsula, where it shut schools and closed ports Monday. In Florida, it will add to the devastation wrought by Hurricane Helene. Milton has the potential to damage some citrus crops and could disrupt voting sites just weeks before the US presidential election.

Milton likely will cause $60 billion to $75 billion in damage and losses, with some models showing the total could rise as high as $150 billion, Chuck Watson, a disaster modeler at Enki Research, said in an X post.

A direct hit on Tampa would likely push damages and losses into the $200 billion range because of valuable real estate in the region, said Jonathan Porter, chief meteorologist at commercial forecaster AccuWeather Inc.

“This can become one of the country’s most damaging and costly hurricanes, due to devastating impacts of the storm occurring in densely populated parts of Florida and also areas with particularly expensive property,” Porter said in an interview. “We are concerned this could be another very significant impact and economic loss.”

The National Hurricane Center is calling for as much as a 15-foot storm surge into Tampa Bay, which would lead to widespread flooding in the city and surrounding area. The topography is flat and there are many smaller inlets, so the water will be able to spread far and wide, said Tyler Roys, a meteorologist with AccuWeather. Port Tampa Bay has closed to all shipping.

In addition to the damage caused by wind and flooding, widespread power outages are likely, said DeSantis, who has declared an emergency in 51 counties.

Milton comes less than two weeks after Hurricane Helene devastated the US South and killed at least 230 people, sparking a wave of disinformation and conspiracy theories. Officials will push to uncover the source of these rumors that have hampered relief efforts, US Federal Emergency Management Agency Administrator Deanne Criswell said.

Disinformation in previous disasters came from US foreign adversaries, Criswell said, and though she doesn’t know if that has been the case for Helene yet, the cause is “certainly something that will be looked into.”

Milton’s top winds have dropped since Monday, in part because the storm was getting larger and undergoing what meteorologists call an eyewall replacement. The storm will also encounter strong vertical crosswinds, or shear, which could reduce its winds further. Still, forecasters warned that Milton is expected to maintain “major hurricane” strength — defined as Category 3 or greater — on its journey across the Gulf of Mexico.

The fluctuations also won’t affect the storm surge it builds up, and history has shown many catastrophic hurricanes notched slower peak wind speeds before making landfall — most notably Katrina in 2005. In addition, the hurricane center said Milton may double its physical size by the time it reaches Florida, exacerbating the risk of serious storm surge.

“Milton has the potential to be one of the most destructive hurricanes on record for west-Central Florida,” Berg said.

US natural gas futures extended declines Tuesday, as traders anticipate a drop in demand for gas to power plants if the storm knocks out electricity. Meanwhile, Chevron Corp. shut in oil production at the Blind Faith platform in the Gulf ahead of the hurricane.

As Milton draws closer, the highest wind gusts are expected to extend well inland to near Orlando and encompass roughly the northern half of the citrus belt, according to Commodity Weather Group.

In addition to Milton, the hurricane center is now watching an area of low pressure off Florida’s east coast that has a 20% chance of becoming a tropical cyclone in the next two days.

--With assistance from Michael Smith, Ilena Peng, Allyson Versprille, Mary Schlangenstein and Ari Natter.

(Updates wind strength in second paragraph.)

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