FORT-DE-FRANCE, Martinique (AP) _ The fourth hurricane to hit the Caribbean in as many weeks _ this one named Marilyn _ raced westward on Thursday, raking Martinique and Dominica and menacing islands westward.

Marilyn threatened to brush past St. Martin, the Dutch-French island devastated by Hurricane Luis last week.

This year's hurricane season is one of the busiest on record, according to the U.S. National Hurricane Center in Miami. There were 14 named tropical storms and hurricanes by Sept. 14 in 1936 and 1993; this year has seen 13.

With 2 1/2 months to go, the season that began June 1 seems set to maintain the frenetic pace set by Hurricane Erin, followed by Hurricane Felix, Tropical Storm Iris and Hurricane Luis. The season runs until Nov. 30.

Heavy seas, high winds and rain squalls hit Martinique on Thursday, causing severe flooding in the southern towns of Francois, Vauclin and Riviere-Pilote.

Strong winds blew roofs off houses on the north coast while flames engulfed one home in Marigot. Authorities could not pinpoint the cause of the fire.

There were no reports of injuries.

Felled trees and power lines blocked roads throughout Martinique, but as the storm left this French island Thursday night, crews from the Public Works Ministry began clean-up operations.

Next in line was Dominica, which lost 90 percent of its vital banana crop to Hurricane Luis last week and the remaining 10 percent fell prey to Marilyn.

Prime Minister Edison James confirmed that a ``substantial'' number of buildings, including a primary school and a church, had lost their roofs due to the 80 mph winds Marilyn is packing.

Several roadways were washed out in the flooding caused by more than six inches of rainfall. Other roads were impassable due to fallen trees and utility poles.

Dominica Broadcast Services reported that an emergency shelter had its roof ripped open while dozens of evacuees weathered the storm. No injuries were reported.

Earlier Thursday, Marilyn damaged 22 homes, downed power lines and uprooted trees in Barbados, about 150 miles southeast of Martinique, said Clive Lord of the Barbados government's Central Emergency Relief Organization. No injuries were immediately reported.

Southern Barbados, where most of the island's tourist resorts are located, was unaffected.

Hurricane warnings were posted as far west as Puerto Rico and the U.S. Virgin Islands and as far north as the Dutch half of St. Martin. Forecasters urged boaters to secure their vessels by Friday morning.

Luis sank 200 boats among hundreds that sought safe harbor in St. Martin last week.

In Puerto Rico, Gov. Pedro Rossello announced that banks will be open only until 11 a.m. Friday and that schools, universities and government offices will be closed. The National Weather Service's San Juan office urged people to take the warning seriously, fearing they might ignore it because of the number of storms.

It was too soon to say whether Marilyn posed a potential danger to the U.S. mainland.

At 11 p.m. EDT, the center of Hurricane Marilyn was about 200 miles east-southeast of St. Croix, according to the National Hurricane Center in Miami. Marilyn was moving toward the northwest at about 13 mph.

Hurricane-force winds extended up to 30 miles from the center, with tropical storm-force winds in a band up to 90 miles beyond that.

The National Hurricane Center said Marilyn was bringing 5 to 8 inches of rain, posing the threat of flash floods and mudslides.

Luis, the most powerful hurricane this season, claimed 12 lives in St. Martin, Antigua, Puerto Rico, Dominica and Guadeloupe before shooting north to Newfoundland last week.

A weak hurricane headed toward Mexico's Pacific Coast late Thursday, packing sustained winds of 80 mph.

The U.S. National Hurricane Center in Florida said Thursday night that Hurricane Ismael was expected to make landfall later in the evening south of Los Mochis, about 750 miles northwest of Mexico City.

At 11 p.m. EDT, Ismael was located some 60 miles south of Los Mochis and was moving at about 18 mph, the hurricane center said. The storm drenched the coast as it made its approach, but there were no immediate reports of damage or injuries.

The storm was expected to quickly lose strength after hitting land, the center said.

Storms are named when steady winds reach 39 mph and become hurricanes if they build to 74 mph.