Members of the Tampa, Florida, Parks and Recreation Dept., help residents with sandbags on Monday, in Tampa, Fla. Residents along Florida's gulf coast are making preparations for the effects of Tropical Storm Idalia. AP

Tropical Storm Idalia closed in on Florida's Gulf Coast on Tuesday after skirting past Cuba, headed for a US landfall as a powerful Category 3 storm, prompting authorities to order evacuations of vulnerable shoreline areas.

Idalia was expected to attain major-hurricane status — with sustained winds topping at least 111 miles per hour (179 kph) — on Wednesday morning before slamming ashore later in the day, according to the Miami-based National Hurricane Center (NHC).

The NHC's latest storm track projections showed Idalia's center likely to cross Florida's coastline somewhere in the Big Bend region, where the state's northern panhandle curves around into the Gulf side of the Florida Peninsula.

The storm's gathering force and the uncertainty of its path as it spun northward over the warm, open waters of the Gulf of Mexico put some 14 million Florida residents under hurricane and tropical storm warnings.

A truck passes by on a flooded street as Storm Idalia makes landfall in Cuba, Guanimar, Cuba, on Monday. Reuters

Authorities said Idalia's chief threat to human life stemmed from surging walls of seawater that would be driven inland by high winds, inundating low-lying coastal areas.

Storm surge warnings were posted for hundreds of miles of shoreline, from the Sarasota area north through Tampa and stretching to the sport fishing haven of Indian Pass at the western end of Apalachicola Bay.

"Buckle up for this one," Florida Governor Ron DeSantis said during a news conference on Monday afternoon.

Idalia is forecast to reach hurricane strength early Tuesday after thrashing the western end of Cuba and was expected to attain Category 3 force - classified as a major hurricane - on the five-step Saffir-Simpson wind scale by the time it makes Florida landfall on Wednesday, the NHC said.

It would mark the fourth major hurricane to strike Florida over the past seven years, following Irma in 2017, Michael in 2018 and Ian, which peaked at Category 5, last September.

Florida Gov. Ron DeSantis speaks during a news conference in Miami. File/AP

In its latest bulletin, the NHC reported Idalia churning about 55 miles (90 km) off the western tip of Cuba as it crept northward, packing maximum sustained winds of 70 mph (110 kph).

Brush with Cuba

Cubans rushed to evacuate coastal towns, batten down homes and tie down fishing boats as Idalia lingered for hours on Monday near the western end of the Caribbean island nation.

By mid-afternoon, chocolate brown floodwaters had swamped the small fishing village of Guan, one hour's drive south of Havana.

Decades-old buses missing floorboards and windows carried women and children to higher ground as winds howled, rattling tin roofs and slamming fishing boats tucked in the mangroves.

Tropical Storm Idalia makes its way to Cuba and Florida's west coast in a composite image. Reuters

"We've had two days of rain already," said Yadira Alvarez, 34, as she readied for evacuation with her five children. "We try to prepare, but no matter what we do everything will be soaked."

Stormwater had already swelled to near knee-height inside her home, she said.

Farther to the west, more intense winds closer to the storm center pounded the tobacco-rich province of Pinar del Rio, home to the raw material for some of the world's finest Cuban cigars.

Authorities had evacuated tens of thousands of people from that province as well as neighboring Artemisa, while squalls of heavy rain doused the Cuban capital of Havana.

Moving to higher ground

Evacuations of barrier islands and other low-lying areas of Florida's Gulf Coast began on Monday.

Shannon Hartsfield, who runs a fishing boat in Apalachicola Bay along the state's panhandle, heeded the warnings, even though he lives west of where landfall was expected.

Hartsfield and many fellow anglers had pulled most of their boats from the bay and moved them to high ground, he said. Others who ran out of time and left their crab traps behind must now wait until after the storm to assess their losses.

A student carries bags at Eckerd College in St. Petersburg, Florida, US, on Monday. AP

"It could jog a little west and come straight at us," Hartsfield said. "Hopefully we won't catch the worst of it."

From Tuesday, Florida's Gulf Coast along with southeastern Georgia and eastern portions of North and South Carolina would face torrential rains of 4 to 8 inches (10 to 20 cm) that could unleash scattered flooding, in addition to tidal inundation from storm surges, the hurricane center warned.

School districts across the region canceled classes starting on Monday afternoon. Tampa International Airport planned to suspend commercial operations beginning at 12:01 a.m. Tuesday.

DeSantis declared a state of emergency for 46 Florida counties. Some 5,500 National Guard troops were mobilized and thousands of electricity workers readied to help restore power quickly after the storm passes.

Far to the east of Idalia, Hurricane Franklin, the first major hurricane of the season, meandered in the Atlantic, and was forecast to turn to the northeast over the next two days. The Category 4 storm threatened to bring heavy swells to Bermuda and the US East Coast throughout the week.

Reuters