Hurricane Milton, which forecasters say poses an "extremely serious threat," is expected to roar into Florida tomorrow.

The fast-growing Tampa Bay region, home to about three million people, hasn’t had a direct hit from a hurricane since 1921. More than 5.5 million Florida residents were urged to evacuate. Patricia Mazzei Jacey Fortin Claire Moses and Judson Jones Patricia Mazzei reported from St. Petersburg, Fla. Millions of people on Florida’s Gulf Coast clogged highways and drained gas pumps on Tuesday as they headed for safer ground, in an exodus that could be one of the largest evacuations in state history ahead of Hurricane Milton. The monster storm exploded Monday into one of the most powerful hurricanes on record. Everyone from local officials to President Biden urged vulnerable residents to flee as it bore down on the vulnerable Tampa Bay region, a metro area of about three million people that hasn’t taken a direct hit from a hurricane in more than a century. As of early Tuesday, 11 counties had issued mandatory or voluntary evacuation orders for coastal and low-lying areas, according to the Federal Emergency Management Agency, which said 5.5 million people were affected by the orders. The number of counties and people in evacuation areas has been steadily rising throughout the day. Milton, the strongest storm in the Gulf of Mexico since 2005, was expected to make landfall on Wednesday, bringing life-threatening hazards to the state for the second time in less than two weeks after Helene swept through. From the White House on Tuesday morning, President Biden called Hurricane Milton “a matter of life and death’’ and urged Floridians to “evacuate now, now, now.” Here’s what we’re covering: Where it’s going: Milton brought strong winds and storm surge to the northern coast of Mexico’s Yucatán Peninsula overnight. Though its wind speeds had come down some — Milton was a Category 4 hurricane by late Tuesday morning, with 150 miles-per-hour winds — it has expanded in size. “We must be prepared for a major, major impact to the west coast of Florida,” Gov. Ron DeSantis said. Track the storm. Tampa’s high risk: The densely populated Tampa Bay region, which is highly vulnerable to storm surge, hasn’t had a direct hit from a major hurricane since 1921. Mayor Jane Castor of Tampa told residents to prepare for “an event like none other,” and said on CNN that if they chose to stay in a mandatory evacuation zone, “You’re going to die.” Emergency aid: Governor DeSantis said he had spoken with President Biden late Monday about what the state needed to prepare. “Everything that we’ve asked for, the administration has approved,” Mr. DeSantis said. FEMA shortages: Stretched thin by Hurricane Helene’s devastation in southern Appalachia, as well as by floods, wildfires, tornadoes and other disasters elsewhere, the Federal Emergency Management Agency now has less than 10 percent of its personnel available to deploy. Here’s how that could affect the agency. Gov. Ron DeSantis cautioned residents across Florida on Tuesday afternoon that Hurricane Milton's effects would not be limited to just the west coast of the state. There will be “significant impacts all across that state,” he said, as the storm moves across the state and eventually out to the Atlantic Ocean. About 8,000 National Guard members will be activated, which is probably the largest mobilization in state history ahead of a storm, Governor DeSantis said. The Florida National Guard cleared debris from Hurricane Helene in St. Pete Beach, Fla. on Tuesday. Hurricane Milton was expected to arrive on Wednesday.Credit...Zack Wittman for The New York Times On the barrier islands outside St. Petersburg, Fla., which were utterly crushed by Hurricane Helene’s storm surge two weeks ago, it was hard to tell where storm recovery ends and storm preparation for the approaching Hurricane Milton begins. Street after street of Pass-a-Grille, a laid-back beach neighborhood in the city of St. Pete Beach, was lined with mountains of debris. The remnants of people’s homes — doors, dressers, mattresses, cookbooks — were heaped about, waiting for pickup. The sand along the water was piled so high that the Gulf of Mexico was hard to see from Gulf Way, the beachfront drag. On Tuesday morning, dump trucks stacked with stuff drove off the island. Florida National Guard crews worked to clear the piles, though the sheer amount of work left to be done seemed impossible to complete before Milton was forecast to arrive on Wednesday night. “They’ve been working all night,” said Pam Flynn, a resident of St. Pete Beach who was packing up her apartment and preparing to evacuate with her husband, Larry Flynn. The couple stayed at the apartment during Hurricane Helene and were surprised by how high the storm surge rose, Mr. Flynn said. Their apartment is on the second floor and was not damaged. But their first-floor neighbors lost almost everything. The Flynns lost both of their cars; their Mazda 6 floated down Pass-a-Grille Way until one of its wheels got stuck in a drain. The Flynns decided to evacuate this time, fearing that Milton would deliver an even higher storm surge and much stronger winds. They had hoped to wait until Wednesday to get out, but changed their mind on Tuesday morning. “One of the die-hards said he was leaving,” Ms. Flynn said. “I said, OK, I think we’re the last ones.” Relatives offered them a place to stay, but they are in Nashville and Chattanooga, Tenn., which seemed too far to drive in jammed storm traffic. So the Flynns plan to head about 20 miles inland and then ride out the storm in their rented minivan, perhaps in a public parking garage. The couple moved to Pass-a-Grille 14 years ago from Kentucky, seeking warmth and sunshine. They have lived through many storms but had never seen a surge like Helene’s. “It was like Armageddon,” said Mr. Flynn, 69. “I’ll never underestimate another one.” Though the Flynns were getting out of town this time, they said they had no plans to leave Pass-a-Grille for good. Some of their downstairs neighbors, however, have already said they’re not sticking around. “It’s going to change forever,” Mr. Flynn said of their beachfront community. “We’ve lost our sense of safety. It’s going to be precarious now.” Nearly 16 percent of Florida gas stations were without fuel as of Tuesday morning, according to GasBuddy, a company that tracks fuel prices. Outages were particularly severe in the Tampa region, where some 43 percent of stations had run dry. In one sign of the urgent efforts to restock gas supplies, Florida officials said the Highway Patrol was providing police escorts to tankers heading out from the ports to gas stations along the evacuation routes. FHP Troopers are working around the clock to escort fuel trucks along evacuation routes ahead of #Milton. Floridians will see FHP utilizing the right lane on highways to bypass traffic and escort fuel carriers from seaports to gas stations. pic.twitter.com/awEFpwSHkC I've been driving through the barrier islands south of Tampa, and it is difficult to describe the extent of the damage from Hurricane Helene two weeks ago. Street after street is piled with debris and discarded possesions. There is damaged furniture everywhere — and practically nobody is around. All of this debris will be incredibly dangerous with storm winds. Hurricane Milton in the Gulf of Mexico on Tuesday morning.Credit...NOAA, via Agence France-Presse — Getty Images Hurricane Milton gained strength over the Gulf of Mexico extremely quickly on Monday, going from a tropical storm to a Category 5 hurricane in under a day. Much of that intensification was fueled by record warm ocean temperatures in the Gulf of Mexico. Global temperatures are rising long term because the burning of fossil fuels adds greenhouse gases to the atmosphere, helping trap heat near the planet’s surface. Hurricane-force winds typically stir up cooler ocean water from below the surface that can weaken a hurricane.