Tropical storm warnings are in effect across southern Florida from Miami to Naples.
Wind gusts to 95km/h are possible over the next day as the storm slides west.
Flooding should be limited, according to the National Weather Service.
Tropical storm warnings are also posted in Louisiana, Mississippi and Alabama, where Gordon will likely make landfall late tomorrow.
The storm will gain strength as it crosses the Gulf of Mexico, though not enough to become a hurricane, according to the National Hurricane Centre.
Much farther east, Tropical Storm Florence is centered 2735km east of the Leeward Islands and poses no threat to anyone for at least a week.
But by the middle of next week, the outlook gets hazy, and a North America impact is not out of the question.
Volleyball courts on Lummus Park Beach, South Beach are empty in Miami Beach.
In this image released by NOAA's GOES-16, Tropical Storm Gordon appears south of Florida.