Based on its internal barometric pressure, Michael was the third most powerful hurricane to hit the USA mainland, behind the unnamed Labor Day storm of 1935 and Camille in 1969.
Shredded trees, derailed train cars and a sunken trailer are seen in the aftermath of Hurricane Michael in Panama City, Fla., Oct. 10, 2018.
More than 375,000 people up and down the Gulf Coast were urged to evacuate as Michael closed in.
Michael grew from a tropical storm to a Category 4 hurricane in about 40 hours.
Storm surge could reach up to 14ft in parts of the hurricane zone.
A total of 453 flights had been cancelled on Wednesday across the country, with many occurring in the Florida area.
The child's death is the second known storm-related death.
"The pressure gives an idea of the size of the storm", he said.
"Going back through records to 1851 we can't find another Cat 4 in this area, so this is unfortunately a historical and incredibly risky and life-threatening situation", he said.
The National Hurricane Center called Michael "potentially catastrophic" and "extremely unsafe".
"Storms like that are referred to in hushed tones", said Phil Klotzbach, a meteorologist at Colorado State University who specializes in Atlantic Ocean hurricane forecasts.
Meanwhile, Michael continues its track across southern Georgia toward the Carolinas. The hurricane's winds and waves were so strong, their rumblings were detected on seismometers - equipment created to measure earthquakes.
"We're sending them out now", Scott said. The areas from Chassahowitzka to Anna Maria Island and between the Alabama-Florida border and the Okaloosa-Walton county line could see 2 feet to 4 feet of storm surge. It had sustained winds of 155 mph, meaning it wasn't from a Category 5 storm - a Category 4 hurricane has sustained winds of up to 156 mph, and Category 5 is 157 mph and above. It is the fourth strongest on record, and nothing this ferocious has ever hit the Panhandle.
The National Hurricane Center predicts Michael will stay a powerful and unsafe rainmaker as it moves across the U.S. Southeast and off the Mid-Atlantic coast before heading out to sea by Friday.
President Donald Trump issued an emergency declaration for Florida, freeing up federal funds for relief operations and providing the assistance of FEMA, which has more than 3,000 people on the ground.
"A potentially catastrophic event is developing", the National Weather Service forecast office serving the Tallahassee area wrote.
About 162,000 homes and business customers were already without power around mid-afternoon in Florida, Georgia and Alabama, utility companies said. Classified as a Category 5 - the highest ranking on the Saffir-Simpson scale - the greatest number of fatalities was in Honduras where severe rainfall led to mud slides and flooding.
After Michael left the Panhandle late Wednesday, Kaylee O'Brien was crying as she sorted through the remains of the apartment she shared with three roommates at Whispering Pines apartments, where the smell of broken pine trees was thick in the air.