A tropical storm watch means sustained winds of at least 39 mph are possible within the watch area within the next 48 hours. "This is when we are Tampa strong".
Murky flood waters are lapping at the entrances to numerous downtown Miami buildings as Hurricane Irma makes its presence known in the state.
But forecasters built in substantial room for error, saying Irma could rake Florida's east coast on a northward path over the Atlantic Ocean toward Savannah at the Georgia-South Carolina line.
In the USA, where it made landfall in Florida state on Sunday, has caused heavy flooding, left about 10 dead and about 6.5 million households without electricity.
Hurricane Irma has been the latest storm to wreak havoc on citizens of the United States and overseas, pounding the states of Florida with winds of incredible velocity and near-constant rain.
Jones warned that some Floridians "may not have power for a number of days, if not weeks".
- One person was found dead in Orange County in a single-car accident linked to the storm, police said without providing details.
Irma is now losing strength, the NHC says.
The warnings pertained mostly to communities along the St. Johns River, where storm surges were expected to push water four to six feet above normal high-tide levels. More than 1.5million customers were without power Monday night in Georgia.
In Coral Gables, near Miami, fallen trees made streets look like jungle, and damaged power lines could be heard buzzing. That risk extended to the coast of Georgia and parts of SC, the hurricane centre said.
"It's my home. I have to try to save it", Burton said.
Prime Minister Theresa May said work was taking place with United States authorities to ensure British expats and tourists in Florida are protected as millions of locals and visitors flee to safety.
It was the first time the eye of a Category 5 storm had made landfall in Cuba since 1932, state media said, and the island's Communist government ordered the evacuation of more than a million people from its path. Irma first came ashore at Cudjoe Key as a Category 4 hurricane with sustained winds of up to 215 kmph.
The fourth victim of the storm was a man in Monroe County who lost control of his vehicle, which was carrying a generator, the Monroe County Sheriff's Office said, as cited by ABC news.
Cooper said during a Saturday morning press conference that all regions of the state can expect to feel the effects of Irma. Besides vertical sheer, tornadoes thrive on an unstable atmosphere - and most instability happens at lower altitudes for a tropical cyclone than for a storm at higher latitudes, NOAA said.
After waiting for hours, South Carolina Gov. Henry McMaster evacuated seven barriers islands and a beach.
And in Alabama, some city school districts including Birmingham, Huntsville and Auburn planned to close Monday and in some cases Tuesday.
The Tampa-St. Petersburg area, with a population of about 3 million, has not taken a direct hit from a major hurricane since 1921.
At least five people died of storm-related injuries in Florida as the massive hurricane barreled across the Sunshine State.
Remnants of Irma have spread gusting winds, rains and misery around the South even as Florida begins cleaning up from one of the most destructive hurricanes in its history, a storm so big it smashed across virtually the entire peninsula.