Caribbean Nervously Awaits Luis : Hurricane: 700-mile-wide storm is shaping up as worst in region in half a century.

With winds gusting up to 160 m.p.h., Hurricane Luis roared Monday toward the Caribbean, where nervous islanders boarded up buildings and frightened tourists jammed airports trying to leave.

The 700-mile-wide storm, with sustained winds of 140 m.p.h., could be the most devastating storm in the Caribbean in half a century, even worse than Hurricane Hugo in 1989. Hurricane watches were posted from Puerto Rico to Dominica.

“We are planning as if the storm is going to directly strike the island,” Puerto Rico’s Gov. Pedro Rossello said in a radio broadcast. “We want to minimize the possibility of loss of life.”

Thousands of San Juan residents stampeded to grocery stores, gasoline stations and hardware shops Monday to stock up on supplies. The shopping spree was so intense that some stores limited the number of shoppers allowed inside.

Rossello suspended a commonwealth law that requires large discount and chain stores to close on holidays. As a territory of the United States, Puerto Rico observed the Labor Day holiday Monday. Puerto Rico’s department of consumer affairs also froze the prices of 43 staple items, including bread, bottled water and milk, to avoid price gouging.

The National Weather Service said tropical storm force winds of about 40 m.p.h. will probably reach the Virgin Islands by midday today and Puerto Rico by this evening.

In the Leeward Islands to the east, at the northern end of the Lesser Antilles, residents had begun stocking up on foodstuffs and other storm provisions days before.

“I think we’re very prepared,” said Arlene Skeet, a resident of St. John’s, the capital of tiny Antigua, which lay directly in the hurricane’s path. “People are holding tight.”

Antigua also prepared for a possible influx of evacuees from Montserrat, where a volcano has been threatening to erupt.

But as the first light breezes of Luis began to stir the palms Monday afternoon, waves of uneasiness also spread.

“We’ve been told to expect winds of up to 150 m.p.h.,” Mike Dowall, a police officer on Anguilla, said in a telephone interview. “We have some new buildings here, and shelters in churches and schools, but I’m worried . . . because these things can do a lot of damage.”

At the National Hurricane Center in Miami, forecasters called Luis a classic, textbook hurricane, with a tight circulation around a well-defined eye embedded in a solid wall of punishing winds. While it is similar in power and path to Hugo, Luis’ wind field is even broader, with tropical storm force winds extending 200 miles north to south.

As a Category 4 storm on the Saffir-Simpson scale, Luis is described as a hurricane with sustained winds between 131 and 155 m.p.h., capable of pushing a storm surge of 18 feet above high tide and inflicting major damage to buildings.

Hurricane Andrew was a Category 4 storm when it raked South Florida in 1992.

In the U.S. Virgin Islands, the National Guard was called into service, and Gov. Roy L. Schneider said he was asking the federal government for emergency help even before the hurricane hit.

“If it misses us, they can tear up the papers,” he said in a radio broadcast.

Tourists thronged the airport at Charlotte Amalie, the capital, but no extra flights were scheduled.

Also Monday, Hurricane Henriette passed the remote tip of southern Baja California in Mexico, toppling trees and power pylons while dumping heavy rains, authorities said.

There were no immediate reports of casualties, but authorities told Mexico’s Televisa network that about 2,000 villagers had been evacuated from coastal areas vulnerable to high tides and flooding.

Army Cmdr. Miguel Estrada Martinez told the Mexican news agency Notimex that troops had gone on alert to help any flood victims. Schools and shops shuttered in the southern Baja city of La Paz.

But Notimex said there was no major storm damage reported in La Paz, about 60 miles north of the peninsula’s southern tip. Television showed footage of palm trees swaying in the blustery winds.