National Hurricane Center is predicting Irma will strengthen into a Category 5 hurricane through the Florida Keys.
Only three other Category 5 hurricanes have hit the US: The so-called "Labor Day" hurricane in 1935, Camille in 1969, Andrew in 1992.
It's still a Category 4 right now — but that's still dangerous.
"THIS IS AS REAL AS IT GETS," the National Weather Service in Key West tweeted. "NOWHERE IN THE KEYS WILL BE SAFE."