Hurricane Bret, unexpectedly and swiftly gathering intensity in the Gulf of Mexico tonight, was forecast to hit the Texas coast late Sunday or sometime Monday with winds that could be as strong as Hurricane Andrew's 145 mph when it devastated Florida seven years ago.

Residents and emergency workers braced for the worst from the first hurricane of the year to threaten landfall.

Bret plodded toward land at speeds ranging from 10 to 14 mph tonight, and earlier slow movement over the gulf's warm water allowed its sustained winds to build to 135 mph, the National Weather Service said. That makes Bret a Category 4 hurricane, which can inflict massive damage on the scale of Andrew and Hurricane Hugo, which hit South Carolina in 1989 with 140-mph winds.

"It's a monstrous hurricane," said Todd Kimberlain, a meteorologist at the National Hurricane Center in Coral Gables, Fla. "There's no other way to describe it."

And Bret was behaving unpredictably. Forecasters had expected it to turn northwest from its northern track and then head west on Sunday, but today Bret held a steady course, which Kimberlain said could send it ashore as far north as Galveston instead of the earlier prediction of the South Padre Island area.

In addition, Bret "continues to intensify," Kimberlain said. At 10 p.m. CDT, forecasters extended the hurricane warning zone, whose southern edge was La Pesca, Mexico, northward to Port O'Connor, Tex., and broadened the watch area to Freeport, which is due south of Houston, because Bret had not veered to the northwest and west as computer models had surmised it would.

As Bret continued to baffle the experts, they issued a highly unusual statement: If Bret's anticipated turn to the northwest and west "does not materialize soon, hurricane warnings will have to be extended northeastward along the Texas coast. Residents and local officials will need to be ready to take quick actions."

If Bret turns west, it could make landfall at one of the least populated areas along the coast: cattle grazing land south of Corpus Christi. If it continues on its northerly track, Galveston and, a bit inland, Houston, could be in its path.

With such an unpredictable storm menacing, people along the coast hurried to make preparations for Bret's arrival, foreshadowed by rainfall tonight south of Brownsville, high surf, 10-foot seas and weather with the potential for tornadoes.

In the small towns and resort areas of the Rio Grande Valley, at Texas's southernmost tip, emergency workers filled thousands of sandbags and planned evacuations, while tourists fled inland and residents crowded gas stations, hardware stores and supermarkets, preparing for the first hurricane to bear down on the Texas coast since 1989.

"We're taking this very, very seriously, and our residents are boarding up their homes and taking all the precautions they should," said Edmund Cyganiewicz, mayor of South Padre Island, one of Texas's most popular resort destinations. South Padre's 2,100 year-round residents and thousands of visitors were ordered to be off the island by 6 a.m. Sunday, the mayor said. About 90 percent of them were gone by tonight, the Associated Press reported.

South Padre, connected to the mainland by a two-mile-long causeway, often hosts 25,000 or more tourists on summer weekends. The island would be lashed by the storm's strongest winds and highest tides if Bret comes ashore south of the Rio Grande. It could be spared the brunt of the storm if Bret makes landfall far to the north.

"Building-wise, our structures are mostly newly developed and will sustain the storm," Cyganiewicz said. "But we expect a lot of coastal flooding."

On the mainland side of the causeway, in Port Isabel, Tex., residents were given until 9 a.m. Sunday to leave. If residents refuse to evacuate, "then we hand out little body tags," Cameron County Judge Gilberto Hinojosa told AP.

Bret, born Wednesday afternoon as a tropical depression in the Bay of Campeche, in the southern gulf, was moving north by northwest this morning with winds exceeding 90 mph, but by tonight, its sustained wind speed had climbed to 135 mph with higher gusts.

As it moved at 8 mph this afternoon over the gulf, its slow speed gave it time to strengthen, said Paul Yura, of the National Weather Service office in Brownsville, in the Rio Grande Valley.

"The warm water is the fuel. It provides all the warm, moist air the hurricane needs."

The Weather Service's earlier hurricane warning had been for a 220-mile stretch of gulf coast, from the small Mexican fishing community of La Pesca to Texas's Baffin Bay, about 25 miles south of Corpus Christi. But as Kimberlain predicted, the zone was expanded late tonight as Hurricane Cindy formed in the eastern Atlantic about 450 miles west of the Cape Verde Islands. The first hurricane to form since the season began June 1, Hurricane Arlene, petered out in the Atlantic.

Flooding from Bret threatened the Texas and Louisiana coasts. The Weather Service issued a coastal flood watch for areas from High Island, east of Galveston, to the lower Atchafalaya River, about 60 miles west of New Orleans.

In Cameron County, which includes South Padre Island and Brownsville, five "colonias"--poorly built housing developments along the border occupied almost entirely by Mexican immigrants--could be devastated by flooding, emergency management coordinator Desi Najera said. He said buses have been readied to ferry the colonias' 7,800 residents and others to shelters.