UPDATE 8-Evacuations ordered as Hurricane Michael speeds toward Florida

(Updates impact on oil and gas platforms, adds Bay County evacuations)

Oct 8 (Reuters) - Florida's governor mobilized National Guard troops and ordered Gulf Coast residents to head inland or get ready to evacuate as Hurricane Michael churned toward shore on Monday, with the storm forecast to strengthen rapidly before making landfall on Wednesday.

Michael was expected to strengthen to a major Category 3 storm by Tuesday with winds over 100 miles per hour (160 km per hour), making it one of the most powerful storms to hit the Panhandle of Florida in decades, state officials said.

The storm was expected to bring up to 12 inches (30 cm) of rain with storm surges up to 12 feet (3.7 meters), according to the U.S. National Hurricane Center (NHC). Michael was currently a Category 1 hurricane, at the bottom of the five-step Saffir-Simpson scale.

Florida Governor Rick Scott declared a state of emergency in more than 20 counties along the Florida Panhandle and Big Bend. Scott advised Gulf Coast residents to prepare for possible evacuation orders, and he put more than 5,000 National Guard soldiers on alert.

"We are running out of time. TODAY is the day to get a plan, because tomorrow could be too late. It is critical that you take care of yourself, your family, and your business as Hurricane Michael approaches FL," Scott wrote on Twitter on Monday.

Michael battered parts of Mexico and Cuba with powerful winds and drenching rains on Sunday and into early Monday.

Tallahassee Mayor Andrew Gillum, who is also the Democratic gubernatorial candidate in the Nov. 6 election, said on Sunday he was cancelling his campaign events and returning to Tallahassee, the state capital, to focus on storm preparations.

Florida State University said its campuses in Tallahassee and Panama City will be closed from Tuesday through Friday. All schools in Panama City and surrounding Bay County will be closed on Tuesday and Wednesday. Leon County officials in Tallahassee were closing all schools from Tuesday through Friday.

Mandatory evacuation orders were issued on Monday for residents in various areas in Florida's Gulf and Bay counties, according to a statement from county emergency officials. Mandatory evacuations were issued for all non-residents in Franklin County, home to various tourist attractions like St. George Island.

Alabama Governor Kay Ivey declared a statewide emergency on Monday ahead of the storm.

Jeff Hanson, the owner of Paisley Cafe in Tallahassee, said he was waiting until Wednesday morning to decide whether he would close the restaurant.

"It depends on what the city says in terms of the people getting around. That's our biggest concern, if our staff is safe," Hanson said by telephone.

OIL PRODUCTION

After hitting Florida, the storm is forecast to move northeast on Wednesday and Thursday along the Atlantic Coast and batter the Carolinas, which are still recovering from Hurricane Florence last month.

Energy companies halted nearly a fifth of Gulf of Mexico oil production and evacuated staff from 10 platforms on Monday as Michael was forecast to become the strongest of three named storms to affect the U.S. Gulf of Mexico this year.

Exxon Mobil Corp, BP Plc, BHP Billiton Ltd and Equinor ASA each pulled staff from production platforms and others were monitoring conditions.

The Gulf of Mexico is home to 17 percent of daily U.S. crude oil output and 5 percent of daily natural gas output, according to the U.S. Energy Information Administration.

More than 45 percent of the nation's refining capacity is located along the U.S. Gulf Coast, which also is home to 51 percent of total U.S. natural gas processing capability.

(Reporting by Gina Cherelus in New York; Additional reporting by Rich McKay in Atlanta and Jon Herskovitz in Austin, Texas; Editing by Paul Simao and Sandra Maler)