Hurricane Floyd, a monster storm drawing comparisons to the devastating hurricanes Hugo and Andrew, bore down on the Bahamas and the southeast coast of the United States today with 155 mph winds approaching catastrophic strength.

Forecasters with the National Hurricane Center urged residents and officials from South Florida to the Carolinas to make preparations for a destructive blow that could strike almost anywhere along the coast, depending on whether the hurricane continues its current westerly course or, as predicted, turns northwest tonight or Tuesday.

More than 1 million people along the Florida coast were advised to evacuate. From the Miami homeowner rushing out to buy plywood to protect his windows to the guardians of the nation's four multibillion-dollar space shuttles housed at the Kennedy Space Center near Titusville, Fla., residents of the most vulnerable areas of Floyd's projected track worked today to get ready for a storm that could be historic in its size and intensity.

"We feel like we've done everything we can to protect these national assets, but it could rip through here like nothing anybody's ever seen before," said Bruce Buckingham, a spokesman at the space center.

Exactly where Floyd might strike remained a deeply troubling mystery today, as forecasters admitted the storm is not following any of their usual models.

A hurricane warning, meaning hurricane conditions could develop within 24 hours, was posted late this afternoon for all of Florida's east coast, from south Dade County to just south of Brunswick, Ga., upgrading a hurricane watch that had been in place since the morning. Although meteorologists at the National Hurricane Center were predicting that a trough of low-pressure would reach down and scoop the storm up the coast, avoiding a direct hit at the Florida shore, the timing was critical. Hurricane-force winds (of at least 75 mph) could still rake the Florida coast.

The storm, which was situated about 360 miles east-southeast of Miami at 11 p.m. today, was still moving west at 14 mph. It was expected to slam into the central Bahamas overnight.

In a mid-morning news conference, Jerry Jarrell, director of the National Hurricane Center, said coastal residents cannot afford to underestimate the fury of Floyd. "I'm very concerned," he said, "we're not taking it seriously enough soon enough."

For now, the storm is so massive and powerful that it almost defies description. Its 155 mph winds place it on the borderline between a Category 4 and Category 5 storm on the Saffir-Simpson scale, with 5 the strongest. Only two Category 5 storms have been recorded since such records were kept: an unnamed "Labor Day Hurricane" in 1935 that left 423 people dead in the Florida Keys, and Hurricane Camille, which struck the Gulf Coast in 1969 and took 256 lives.

The storm could strike directly later in the week in the Charleston, S.C., area, or near the North Carolina-South Carolina border, or even as far north as the Outer Banks of North Carolina, Deputy Director Max Mayfield said at another late-afternoon news conference.

Although the storm already is as intense as Hurricane Andrew, which caused $26 billion in damage and 26 deaths when it struck South Florida on Aug. 24, 1992, it is as much as four times larger. Floyd's hurricane-force winds extend 105 miles to the northwest from its center, whereas with the compact Andrew, such winds extended only about 25 miles, said National Hurricane Center meteorologist Todd Kimberlain.

Floyd already is slightly stronger than Hugo, which assaulted the Charleston area in 1989, resulting in $10 billion in damage and 21 deaths, although its massive dimensions are similar, Kimberlain said.

"A good analogy is, it looks like a super-typhoon, like something you find in the Pacific Ocean," he said, noting the very well-defined eye with the most powerful winds wrapped tightly around it and a cloud cover that spans an astonishing 800 miles.

Florida Gov. Jeb Bush (R) declared a state of emergency today. "This will allow the state to coordinate with local and federal officials as closely as possible," he said, " . . . so all vulnerable areas will be prepared."

If Floyd strikes head-on along the Florida coast, it could affect some of the most densely populated areas along the eastern seaboard, along with some of the most expensive -- and fragile -- dwellings along the beaches.

In Brevard County, on the east-central Florida coast, just south of the Kennedy Space Center, tens of thousands of residents living in mobile homes and in low-lying areas were ordered to begin evacuations.

Ten evacuation shelters began opening in the Miami-Dade County area at 6 p.m. today for residents of the barrier islands and mobile homes, and those with special needs, although forecasters were sticking with their prediction that Miami would miss the worst. Schools and libraries in the area will be closed on Tuesday. Broward County just to the north also began opening a dozen shelters this evening.

At NASA's Kennedy Space Center, "We are in full-tilt mode," Buckingham said today, "making sure the shuttles and the payloads are being protected."

But there was only so much workers could do, since there is not enough time to move the shuttles. The four orbiters, which would cost about $2 billion each if they had to be replaced, Buckingham said, are housed in facilities that can withstand winds of 105 mph to 125 mph, much less than Floyd would pack were the storm to make a direct hit.

Special correspondent Catharine Skipp contributed to this report.

CAPTION: BRACING FOR A BIG ONE? (This graphic was not available)