MIAMI • Hurricane Michael gained new strength Monday and is expected to keep growing stronger ahead of an expected midweek strike on Florida’s Panhandle, forecasters said.

Michael could become a major hurricane with winds topping 111 mph by Tuesday night before the anticipated landfall Wednesday on the Panhandle or Big Bend, according to the National Hurricane Center.

Since the storm will spend two to three days over the Gulf of Mexico, which has very warm water temperatures and favorable atmospheric conditions, “there is a real possibility that Michael will strengthen to a major hurricane before landfall,” Robbie Berg, a hurricane specialist at the Miami-based storm forecasting hub, wrote in an advisory.

Michael’s large size, strong winds and heavy rains could produce hazardous flooding along a stretch of Florida’s Gulf coast with many rivers and estuaries where seawater pushed ashore by a hurricane could get trapped, said Hurricane Center Director Ken Graham.

“This is a part of the Gulf of Mexico that is incredibly vulnerable to storm surge,” Graham said.

Parts of Florida’s curvy Big Bend could see up to 12 feet of storm surge, while Michael also could dump up to a foot of rain over some Panhandle communities as it moves inland, forecasters said.

Mandatory evacuation orders were issued for residents of barrier islands, mobile homes and low-lying coastal areas in Gulf, Wakulla and Bay counties.

In a Facebook post Monday, the Wakulla County Sheriff’s Office said no shelters would be open because Wakulla County shelters were rated safe only for hurricanes with top sustained winds below 111 mph. With Michael’s winds projected to be even stronger than that, Wakulla County residents were urged to evacuate inland.

“This storm has the potential to be a historic storm, please take heed,” the sheriff’s office said in the post.

A large mound of sand in Tallahassee was whittled down to a small pile within hours Monday as residents filled sandbags to prepare for potential flooding.

A couple breweries in the city offered free filtered water to anyone bringing in growlers, jugs or other containers.

“All indications are that it’s going to be severe,” said City Commissioner Gil Ziffer, adding that if the storm hits Florida’s capital, there would be significant tree damage and power outages. “Hopefully we will have no one hurt and no loss of life.”

This satellite image provided by the National Oceanic and Atmospheric Administration shows a view of Hurricane Michael, lower right, churning as it heads toward the Florida Panhandle on Sunday.

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