If you just think about the current evac zones- the Keys and A and B in most of SoFla,
Zones A and B are full of huge high rises up and down the coast, houses too, but hundreds of high rises.
I have no clue what that number of people would be, but it has to be several hundred thousand...if not at least 1 million or more.
Combine that with all of the people who are voluntarily evacuating, I can't even imagine.
ETA- this is ONLY one part of Miami, and only a portion of evacuees.
The U.S. city of Miami, Florida has the country's third-tallest skyline with over 300 high-rises, 70 of which stand taller than 400 feet (120 m), mainly according to Emporis,[1]SkyscraperPage, and The Skyscraper Center, which is the online database of the Council on Tall Buildings and Urban Habitat. The tallest building in the city is the 84-story Panorama Tower, which rises 868 feet (265 m) in Miami's Brickell district and on March 24, 2017 surpassed all other buildings in height. It is to be completed by the end of 2017. Eight of the ten tallest buildings in Florida are located in Miami. By 2020 there will be 10 more buildings in Florida with more than 65 stories each.