MIAMI (REUTERS) - Hurricane Michael grew into a major Category 3 storm as it howled closer to Florida's Gulf shore on Tuesday (Oct 9), sending tens of thousands of coastal residents fleeing to higher ground one day before its expected arrival with towering waves and roof-shredding winds.

Michael is projected to plough into Florida's panhandle at midday on Wednesday, unleashing potentially devastating waves of seawater as high as 3.6m that could rush inland for miles around the storm's centre, the National Hurricane Centre (NHC) warned.

By Tuesday, Michael was already causing major disruptions to US oil and gas production as it churned north over the Gulf of Mexico.

President Donald Trump declared a state of emergency for the entire state of Florida, freeing up federal assistance to supplement state and local disaster response.

At latest report, the NHC said the storm was packing sustained winds of up to 195kmh, jumping from a Category 2 to Category 3 hurricane on the five-step Saffir-Simpson wind scale.

Winds of that magnitude can inflict substantial damage to roofs and walls of even well-constructed homes, according to the National Weather Service.

The storm also is likely dump prodigious amounts of rain over Florida, Alabama, Georgia and the Carolinas - still recovering from severe flooding last month in the aftermath of Hurricane Florence. Up to a foot of rainfall (30cm) is forecast for some areas.

"This is a storm that is going to be life-threatening in several ways," said Bo Patterson, the mayor of Port St Joe, Florida, whose small beachfront town lies directly in the storm's projected path.
"Hurricane Michael is a monstrous storm and the forecast just keeps getting more dangerous, we are now just hours from seeing impacts," Florida Governor Rick Scott said on Tuesday afternoon.

"If you don't follow warnings from officials this storm could kill you," said the Republican governor, who is campaigning for a US Senate seat in the November congressional elections.

Producers in the US Gulf of Mexico on Tuesday cut oil production by about 40 per cent and natural gas output by 28 per cent as Michael approached the coast, the Bureau of Safety and Environmental Enforcement said, citing reports from 27 companies.

The Gulf produces 17 percent of daily US crude oil output and 5 percent of daily natural gas output, according to the US Energy Information Administration. The partial shutdown ahead of Michael helped push oil prices slightly higher on Tuesday.

Scott declared a state of emergency in 35 counties in Florida's Panhandle and Big Bend regions, mostly rural areas known for small tourist cities, beaches and wildlife reserves, and the state capital, Tallahassee.

The hurricane was forecast to deliver as much as 30cm of rain in parts of Florida, Georgia and South Carolina. Western Cuba was also forecast to get torrential rains.

The Federal Emergency Management Agency had numerous teams deployed and ready to respond, said Fema spokesman Jeff Byard. About 2500 National Guard soldiers were assisting and more than 4,000 troops were on standby. Some 13,000 utility restoration workers were also on standby.

President Donald Trump told reporters at the White House the country was very well prepared for the hurricane, adding it was much bigger than had been expected.

'BUTTONED UP, TIGHTENED DOWN'

In Panhandle counties, most state offices, schools and universities were closed for the rest of the week. Lines at gasoline stations grew as people left. Those who stayed emptied grocery store shelves of water and other supplies.

Gary Givens, owner of Gary's Oyster Shack in Panama City, Florida, said he was closing his restaurant around lunchtime on Tuesday with the help of his crew ahead of the storm's arrival. But Givens said he was staying put because he owns two businesses in the area.

"I just got a crew that came in that are staying also and they're in here helping me get everything buttoned up, tightened down, getting the food secure," Givens said.

Some Panama City residents were on the beach enjoying a cool breeze ahead of the storm, while others were loading up cars with luggage, and visitors were checking out of hotels.

The last major hurricane to hit the Panhandle was Hurricane Dennis in 2005, according to hurricane centre data.

At 2pm ET (2am on Wednesday Singapore time), Michael's centre was about 500km south-southwest of Apalachicola, Florida, heading north at around 19kmh, the NHC said.

On its current track, it would hit land somewhere along a coastline that includes the cities and towns of Fort Walton Beach, Panama City Beach, Port St. Joe, St Teresa and the wildlife reserves bordering Apalachee Bay. However, forecasters always note it is not possible to say where a hurricane will land until it is closer to the coast.

A hurricane warning was in effect for the coastline from the Florida-Alabama border to the Suwannee River in Florida.

Torrential downpours and flash flooding from the storm over the weekend caused 13 deaths in Central America.

The storm was forecast to move through the southeastern United States on Wednesday night and Thursday, passing through Georgia and the Carolinas, which are still recovering from Hurricane Florence last month. It would head off the Mid-Atlantic coast by Friday, the NHC said.

Georgia Governor Nathan Deal declared a state of emergency on Tuesday for 92 counties in the state.