"Michael is likely to produce potentially catastrophic wind damage where the core of the hurricane moves onshore in the Florida Panhandle, and everyone in the hurricane warning area should prepare for life-threatening hurricane winds".
There was a storm surge warning in effect from the Okaloosa/Walton county line to the Anclote River in Florida, and a storm surge watch in effect from Ocracoke Inlet, N.C., to Duck, N.C.
Along with the mandatory evacuation orders come a notably tighter security.
Officials warn that the low-lying Florida Panhandle is extremely vulnerable to storm surge, with a geography that could concentrate vast amounts of ocean water and flood homes and businesses. A storm with that power hasn't struck the Florida Panhandle since Hurricane Dennis in 2005. A sign at the restaurant located just across from the beach on Highway 30-A says it plans to "open as soon as the storm passes".
Based on its internal barometric pressure, Michael was the third most powerful hurricane to hit the USA mainland, behind the unnamed Labor Day storm of 1935 and Camille in 1969. The major hurricane had moved within 40 miles of Panama City and 35 miles of Mexico Beach.
The lower the minimum pressure, the more intense the hurricane.
Category 4 storms pack winds from 130 to 156 miles per hour and cause "catastrophic damage", according to the Saffir-Simpson hurricane scale. A storm surge of almost 8 feet was reported at Apalachicola.
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Alabama Gov. Kay Ivey issued a statewide state of emergency, saying on Twitter it was "in anticipation of wide-spread power outages, wind damage and debris produced by high winds & heavy rain associated with Hurricane Michael".
Michael also had hot towers - tall thunderstorms that form in the eyewall of a hurricane - and these storms release heat that all the water vapor condenses into cloud water.
At 2:00 a.m. Wednesday, the eye of Michael was about 180 miles (289 kilometers) south-southwest of Panama City, Florida.
One forecast model from the University of MI estimates the storm will result in 1.4 million people losing power throughout the Southeast.
Based on wind speed, it was the fourth-strongest, behind Andrew in 1992, Camille, and the biggest one of all, an unnamed 1935 Labor Day storm that had winds of 296kph.
Several hours ahead of landfall, seawater was already lapping over the docks at Massalina Bayou near downtown Panama City, and knee-deep water was rising against buildings in St. Marks, which sits on an inlet south of Tallahassee.
"As Michael moves across the southeastern United States, it could bring three to six inches of rain to the remainder of Georgia, the Carolinas and southern Virginia".
Meanwhile, Hurricane Michael is now predicted to reach a level close to category 4 when it hits the U.S. state of Florida on Wednesday. According to The Weather Channel, no Category 4 hurricane in historical records dating back to 1851 has ever made landfall in the region. That's how strong a storm can get if all other factors are aligned, said National Oceanic and Atmospheric Administration climate and hurricane expert Jim Kossin said.