Eta made landfall late Sunday night in the state's Lower Matecumbe Key, the BBC quoted the National Hurricane Centre (NHC) as saying in its latest update on Monday.
In the update, the NHC warned that Eta would bring "strong winds, heavy rains and dangerous storm surge" over parts of South Florida and Florida Keys.
The storm had brought maximum sustained winds of 100km/h, was moving at around 22km/h and is forecast to become a hurricane as it moves over the south-eastern Gulf of Mexico.
As much as 12 inches of rain could fall and storm surges could reach as high as 4ft, the update added.
As the storm was still approaching, schools, beaches and public transport across the southern part of the state were closed.
Eta killed 26 people in Honduras, 17 in Panama and 20 in Mexico.
While Guatemalan President Alejandro Giammattei said last week hat the death toll due to the tropical storm could reach 150.
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