Hurricane Gustav dropped to a Category 3 storm as it rolled across western Cuba early Sunday, but forecasters predicted it would regain strength as it roared through the Gulf of Mexico to a landfall on the Louisiana coast sometime during the day on Monday.
President Bush and Vice President Cheney, mindful perhaps of the criticism they received for not canceling vacations during Hurricane Katrina three years ago, canceled their appearances at the Republican convention, which opens in St. Paul, Minn., on Monday.
More than a million fled New Orleans and other coastal areas Saturday, and a staged evacuation of New Orleans began early Sunday and will last until weather conditions deteriorate late in the day.
Gustav was nearly a monstrous Category 4 storm when it made landfall on mainland Cuba in the tobacco-rich Pinar del Río province. Hundreds of thousands evacuated the area and the Isle of Youth just south of the main island. Gustav left behind shattered windows, downed trees, torn-off roofs and washed-out roadways.
Cuban Civil Defense chief Ana Isla said there were ''many people injured'' on Isle of Youth, but no fatalities had been reported. ''It's been very difficult here,'' Isla said on state television, noting that power and telecommunications were out.
As of Sunday morning, Hurricane Gustav was about 375 miles southeast of the mouth of the Mississippi River and heading northwest at 16 mph.
Forecasters Sunday morning offered hope that the storm would not become a Category 5 storm, the top measurement of hurricane intensity. Wind shear, dry air and a "ragged storm structure'' will likely prevent Gustav from rapidly intensifying, said Jack Beven, a senior hurricane specialist at the National Hurricane Center.
But Gustav is still expected to be ferocious when it slams into the Gulf Coast with winds of with winds of 130 to 135 mph winds. The storm surge could be as high as 20 feet, testing the area's rebuilt levees that Hurricane Katrina overwhelmed three years ago.
"Make no mistake about it," National Hurricane Center spokesman Dennis Feltgen said. "This one's going to be strong."
New Orleans Mayor Ray Nagin called Hurricane Gustav the "mother of all storms'' and ordered residents to leave.
"Get out of town," Nagin said. "This is not the one to play with. You need to be scared."
People living in the city's western suburb of Jefferson Parish, which was swollen by residents who did not return to New Orleans after Katrina, also were ordered to evacuate. It was the first mandatory evacuation for the entire parish.
The city will not offer emergency services to those who choose stay behind, Nagin said, and there will be no ''last resort'' shelter as there was during Katrina, when thousands suffered inside a squalid Superdome.
City officials said anyone not on their property after the mandatory evacuation started would be subject to arrest.
Fearing more than a foot of rain and a potential storm surge that could overwhelm the city's partially rebuilt levees, millions packed up and evacuated. Bumper-to-bumper traffic was reported on highways leading out of the area, and officials instituted the contraflow system of making all major roadways one-way so people could flee faster.
A landfall about 30 to 50 miles west of the city is likely, but hurricane-force winds and significant storm surges are possible for a wide swath of the northern Gulf.
''Even if it falls just west of New Orleans, people in that whole neighborhood are going to feel the effects of a major, major hurricane,'' said Dennis Feltgen, a meteorologist and spokesman for the National Hurricane Center in West Miami-Dade County.
The hurricane center issued a hurricane warning extending from High Island, Texas, to the Alabama-Florida border. Northbound lanes out of New Orleans saw bumper-to-bumper traffic as residents fled on Saturday, one day after the three-year anniversary of Hurricane Katrina's devastating landfall.
Meanwhile, Sen. John McCain flew to Mississippi with his wife, Cindy, and his running mate, Alaska Gov. Sarah Palin, where they were to receive a breifing at FEMA headquarters in Jackson. In St. Paul, Republican convention organizers said they might change the convention schedule and theme to stress service in the face of the storm.
''It just wouldn't be appropriate to have a festive occasion while a near-tragedy or a terrible challenge is presented in the form of a natural disaster,'' McCain told Fox News in an interview taped for Sunday. ``So we're monitoring it from day to day and I'm saying a few prayers, too.''
Governors Bobby Jindal of Louisiana and Rick Perry of Texas decided not to attend the convention, instead opting to remain in their states during the storm.
Gustav left a mounting death toll in the Caribbean, with at least 94 confirmed fatalities: 76 in Haiti, eight in the Dominican Republic and 10 in Jamaica.
No fatalities were reported in the Cayman Islands, where Gustav's winds toppled power lines and snapped trees and light poles. The government issued an all-clear declaration, signaling that the danger had passed.
Oil companies evacuated workers and shut down oil platforms in the Gulf of Mexico in anticipation of Gustav's arrival. The shutdown had not caused a spike in gas prices at the pump yet, but analysts say that could happen next week depending on the damage Gustav inflicts. In 2005, Hurricane Katrina disrupted 95 percent of the Gulf's oil output.
Computer models that estimate a storm's track showed more consensus Sunday about Gustav's landfall being near central Louisiana, just west of New Orleans, before jogging west into Texas and dissipating.
National Guard soldiers on Mississippi's coast were going door-to-door to alert thousands of families in FEMA trailers and cottages that they should evacuate.
''Make no mistake about it,'' Feltgen said. "This one's going to be strong.''