As Hurricane Irma bore down on South Florida on Saturday, meteorologists and hurricane experts had a dire message for local residents: Hurricane Irma is strong enough to kill you.
“This is a life-threatening situation,” said Mike Brennan, the center’s chief hurricane specialist, nodding into a scrum of television cameras at the National Hurricane Center, a squat concrete building just west of Miami International Airport. “We’re looking at potentially catastrophic storm surge values and you’re running out of time.”
Hurricane Irma, among the biggest hurricanes ever recorded in the Atlantic, made landfall over Cuba Friday, which temporarily weakened the storm, knocking it down from a Category 4 to a Category 3 hurricane, according to forecasts by the National Oceanic and Atmospheric Administration.
“But we don’t want people to focus on that,” Brennan told TIME. As the storm passes over the warm water between Cuba and South Florida, it will likely increase in intensity yet again. “This thing has been so resilient. It’s going to get strong again.”
Residents who think they can just “ride this one out” as they have smaller storms in the past are fooling themselves, said Jamie Rhome, who runs the storm surge team at the Hurricane Center. “Not only is that wrong, but thinking that way could cause you to lose your life,” he warned.
The track of the massive storm has shifted slightly west during the past 24 hours, according to forecasts. NOAA now forecasts Irma crawling up the southwest coast of Florida into Sunday night, and slamming into Tampa on Monday.
Mark DeMaria, acting deputy director at the National Hurricane Center, said that since the hurricane is now less than 24 hours away from landfall in Florida, predictions are becoming more reliable. “It could shift a bit eastward and spare Tampa,” he told TIME, tracing his finger in northward arc along a digital map. “But at this point, we can’t say exactly.”
Tens of thousands of residents of the Florida Keys and Miami-Dade County evacuated from their homes in recent days. Many went to stay with friends and relatives in Tampa and Orlando, which until recently had appeared to fall outside the center of the storm.
Today’s forecast changes that outlook.
“What had seemed like a better choice might not be at this point,” Brennan said. “My family is dealing with this, too. They weren’t sure where to try to go. The storm is so big that where ever you are, you have to prepare.”
Behind the cameras, Dennis Feltgen, the public affairs officer at NOAA, worried about Tampa. “Tampa’s going to be underwater,” he said. “Five to eight feet.”
Storm surges in southwest Florida are expected to reach 10 to 15 feet, forecasts say, enough to put a one-story home underwater. The most vulnerable include the Keys and communities on the west coast of Florida, from Cape Sable to Capitiva Island, west of Fort Meyers.
Residents of the Florida Keys and parts of Miami-Dade County, as well as of Orlando, Tampa and other Florida cities now have mandatory evacuation orders for vulnerable neighborhoods. The Hurricane Center is warning of tropical-storm force winds all the way up to Georgia, and hurricane warnings are in effect in much of the southeast coast of the U.S., from the Keys up to South Carolina.
“This is an extremely urgent situation,” Brennan said, almost pleading into the television cameras. “You may only have to go only a few miles inland. You still have a few more hours.”
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Write to Haley Sweetland Edwards/Miami at haley.edwards@time.com