(Adds storm's wind speed in paragraph 7)
By Alana Wise
Sept 4 (Reuters) - Hurricane Irma, barreling toward the Caribbean and the southern United States, was upgraded to a powerful Category 4 storm on Monday as islands in its path braced for a possible onslaught.
Hurricane advisories were issued for territories that dot the West Indies, including parts of the Leeward Islands, the British and U.S. Virgin Islands and Puerto Rico, in preparation for the intensifying storm that could pummel the area with life-threatening wind, storm surges and torrential rain by Tuesday evening, according to the U.S. National Hurricane Center (NHC).
Ahed Daas, owner of the Food Center in St. Thomas, U.S. Virgin Islands, said traffic at his store on Monday was about 50 percent higher than normal as people stocked up on water, canned products and batteries. Since it is the off-season for tourists, almost all the customers are local and there were few liquor sales.
People began to shop as early as last week as Irma neared and continued through the weekend.
"It’s kind of dwindling down now, everybody’s pretty much stocked up," Daas said. "You make sure you have fuel in your generator and hope it’s not that bad when it does arrive."
A Category 4 hurricane on the five-step Saffir-Simpson scale means sustained winds of 130-156 miles per hour (209-251 kph) with "catastrophic" outcomes, including uprooted trees and downed power lines, water and electricity outages, and significant property damage causing uninhabitable conditions, according to the Miami-based hurricane center.
Irma, now packing 140 mph (220 kph) winds, also threatens the U.S. East Coast and Florida, which on Monday evening declared a state of emergency. The hurricane center expects Irma to reach southern Florida on Saturday.
The NHC cautioned that it was too early to forecast the storm's exact path or what effects it might have on the continental United States, but warned of likely effects to hit some areas by later this week.
"There is an increasing chance of seeing some impacts from Irma in the Florida Peninsula and the Florida Keys later this week and this weekend. In addition, rough surf and dangerous marine conditions will begin to affect the southeastern U.S. coast by later this week," the center said.
Irma will be the second powerful hurricane to thrash the United States and its territories in as many weeks.
Residents of Texas and Louisiana are still reeling from the catastrophic effects of the deadly Hurricane Harvey, which struck Texas as a Category 4 hurricane on Aug. 25 and dumped several feet of rain, destroying thousands of homes and businesses.