TAMPA, Florida (BLOOMBERG) - Ian made landfall over western Cuba as a major Category 3 hurricane, while churning towards Florida in what could be the worst storm to hit Tampa in over a century.

Ian's winds jumped to 205kmh as it neared the city of Pinar Del Rio, Cuba, according to an advisory from the US National Hurricane Centre at 5am New York time. It was still about 281km from Florida's Dry Tortugas.

The Tampa area is now at the centre of the probability track forecasts as the storm moves northward.

Hurricane and storm surge warnings are in effect along Florida's west coast, including Tampa Bay.

More than 300,000 people are expected to evacuate.

"This is a life-threatening situation," Mr Brad Reinhart, a hurricane specialist at the centre, said in his analysis.

"Promptly follow evacuation and other instructions from local officials."

Tropical storm winds could reach Florida on Tuesday, with hurricane conditions arriving on Wednesday morning, bringing the potential for significant river flooding across central parts of the state.

Hurricanes reach "major" or Category 3 status on the Saffir-Simpson scale when their maximum sustained winds hit 178kmh.

Parts of western Cuba are set to receive as much as 41cm of rain through Thursday, according to the hurricane centre.

Flash flooding and mudslides could occur.

Cuban President Miguel Diaz-Canel warned the nation on Monday that it would be facing a "challenging week".

Ian will ride up Florida's west coast. The state will very likely see widespread surge, wave and rain impacts no matter where it hits, Dr Ryan Truchelut, president of WeatherTiger, said in an e-mail.

Its winds are forecast to peak at 225kmh late on Tuesday through Wednesday, before dropping to 193kmh on Thursday, the centre said.

The storm will encounter wind shear in 36 to 48 hours, which will hold it back from gaining even more strength.

Still, Hurricane Ian could be the worst storm to hit Tampa in 101 years, according to Mr Chuck Watson, a disaster modeller with Enki Research.

The area has had many close calls in recent years, but the last devastating strike on the Tampa-St Petersburg area was a 1921 storm that would have cost US$30 billion (S$43.07 billion) today.

On its current track, Ian could bring tropical-storm strength winds to more than half the orange-growing acreage in the state, Mr Watson said.

Fuel and fertiliser

Demand for diesel for generators in Florida has soared by more than 10 times the norm, said Mr Eliot Vancil, president of Fuel Logic, a distributor in the state.

Requests are coming from nursing homes, grocery stores, hospitals and the like, with demand heavily focused in Tampa, he said in a phone interview.

There is no shortage of fuel in the state yet, but "there is a shortage of time to get it done" before the storm, he said.

Fertiliser producer Mosaic said it is finishing storm preparations at its phosphate mining and production facilities in Florida and sites in Louisiana.

Employees at its headquarters in downtown Tampa and other Florida locations are working remotely.

Ian is expected to miss most of the energy infrastructure in the Gulf of Mexico, though Chevron and BP said they have shut some offshore oil production platforms in the region and evacuated employees ahead of the storm.

It is forecast to be a major hurricane off Hillsborough County, which includes Tampa, and could push a storm surge of 4.5m into the shoreline, Mr Tim Dudley, county emergency management director, said in a YouTube post.

Mandatory and voluntary evacuation orders have been issued and the county is opening shelters, Ms Bonnie Wise, the county administrator, said in a briefing posted on YouTube.

The county expects to evacuate more than 300,000 people, she said.

Tampa Electric said on Monday it may proactively cut power to a part of downtown Tampa early on Wednesday to avoid serious damage to its equipment from an expected saltwater storm surge.

Tampa International Airport will suspend operations at 5pm on Tuesday, and American Airlines Group issued a travel alert for 20 airports in the western Caribbean and Florida.

Tampa tourist attraction Busch Gardens will close on Tuesday and Wednesday, and the Tampa Bay Buccaneers football team will use the practice facility of their cross-state rivals, the Miami Dolphins.

President Joe Biden approved an emergency declaration for Florida on Saturday, freeing federal disaster aid to the state.

He also postponed a scheduled trip on Tuesday to the state that included a Democratic National Committee rally in Orlando.

Governor Ron DeSantis declared a state of emergency across Florida and warned residents to prepare.

Ian is the second destructive hurricane to rip across the Atlantic in less than a week, following Hurricane Fiona.

Fiona struck Atlantic Canada over the weekend, causing extensive damage, power outages and flooding across Nova Scotia and Prince Edward Island.

Damage to the region is estimated at US$3.5 billion, though secondary factors and rain may push costs above US$4.5 billion, according to Enki Research's Watson.