Updated 10:06 a.m. ET
Hurricane Michael has been upgraded to a "potentially catastrophic" Category 4 storm, with maximum sustained winds of 145 mph, the National Hurricane Center says. Tropical-storm-force winds began hitting the Florida Panhandle Wednesday morning, and water levels were quickly rising.
Just before 10 a.m. ET, the storm was 65 miles south-southwest of Panama City, Fla., moving north at 13 mph. Michael could get even stronger from warm water in the Gulf of Mexico before making landfall in the Florida Panhandle on Wednesday, forecasters say.
It would be the first Category 4 storm to hit the Florida Panhandle since records were first kept in 1851, said NHC Director Ken Graham.
"This is definitely [and] unfortunately a historical and incredibly dangerous and life-threatening situation," he added.
The storm's center is currently on track to make landfall "pretty close to Panama City" on Wednesday afternoon, Graham said. But he warned people who live miles away to be prepared for the hurricane's "incredibly damaging" winds and storm surge.
Michael is expected to bring life-threatening flash floods and storm surges throughout coastal areas along the Gulf, from Pensacola around the coast to Tampa.
Flooding has already begun in some areas; the National Weather Service office in Tallahassee posted a photo of a building near Panacea, Fla., with water seeming to cover its lower third around 6:30 a.m. local time.
With the storm powering toward the coast, the Weather Channel's Mike Bettes said he and his crew were leaving Apalachicola, adding, "Better safe than sorry."
The storm's winds exploded in strength overnight, with an Air Force Reserve Hurricane Hunter aircraft reporting maximum sustained winds of 145 mph shortly before 8 a.m. ET.
With the storm possibly growing even stronger, NHC scientist Eric Blake called it "a near worst-case scenario for the Florida Panhandle."
The hurricane center has raised its estimates of the storm surge, saying ocean water could reach levels of 9 to 14 feet aboveground in a central area around Apalachicola. For miles on either side, low-lying areas could see a surge of 6 to 9 feet.
With the storm on Florida's doorstep, Gov. Rick Scott told residents Wednesday morning, "it is not safe to travel across the Panhandle. [If you are in a coastal area], do not leave your house. The time to evacuate in coastal areas has come and gone."
Those further inland, Scott said, might be able to seek shelter if local officials say it is safe. Otherwise, residents should prepare to endure the storm at home.
"The worst thing you can do now is leave, and put yourself and your family in danger," Scott said.
There are currently 54 shelters open across the Panhandle and Big Bend areas, Scott said, adding that more than 1,000 search and rescue personnel will be deployed after the hurricane passes through.
"We have trucks loaded with tons of food, water and other critical supplies, ready to move in," Scott said.
The NHC predicts Michael's center will move inland over the Florida Panhandle or Big Bend area before moving northeast across the southeastern U.S. Wednesday night and Thursday. It will then move off the East Coast — but as it does so, it will also regain some strength from the Atlantic Ocean.
Areas along the coast and inland, miles from the expected landfall zone, will be at risk from this strong and large storm. With its winds at nearly twice the minimum for hurricane status, Michael could remain a hurricane into early Thursday morning — a time when forecasters expect it to have plowed into southern Georgia.
The surge of water began arriving late Tuesday, ahead of the main storm and before its heavy rains, which will come as drainage systems are already trying to cope with the ocean water surge.
Water pushed ahead by Michael mixed with high tides on Tuesday afternoon to cause minor flooding in a number of areas on Tuesday afternoon, from Tarpon Springs to Sarasota — an area that includes Tampa Bay, as member station WUSF reports.
Some 300 miles of coastline remain under storm surge, hurricane and tropical storm warnings. Storm surge warnings continue, from the Okaloosa County-Walton County line to the Anclote River. Another spans from the Anclote River to Anna Maria Island, including Tampa Bay.
Tropical storm warnings are now in effect in the Carolinas, from South Santee River, S.C., to Surf City, N.C. Much of the Alabama coast is also under warning.
Residents of the Panhandle and Big Bend face enormous predicted storm surges, the likes of which could destroy homes, according to the National Weather Service. The NHC predicts these coastal regions can expect 9 to 13 feet of storm surge, as the Michael's winds force a wall of water onto the low-lying shore.
Category 4 storms pack winds from 130 to 156 mph and cause "catastrophic damage," according to the Saffir-Simpson hurricane scale. Here's how the scale describes a Category 4's potential effects:
"Well-built framed homes can sustain severe damage with loss of most of the roof structure and/or some exterior walls. Most trees will be snapped or uprooted and power poles downed. Fallen trees and power poles will isolate residential areas. Power outages will last weeks to possibly months. Most of the area will be uninhabitable for weeks or months."
Looking ahead to the aftermath of the storm and the likely downed trees and utility lines, Graham said, "You have to stay away from those power lines. If you have trees down, it's not the time to start learning how to use that chainsaw."
People should also keep their generators outside, he added, to avoid being overcome by toxic fumes.
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