Hurricane Katia powered up to a major Category 4 storm on Monday, but was expected to veer away from the U.S. East Coast later this week, avoiding a direct hit on a seaboard already battered by Hurricane Irene.
The U.S. National Hurricane Center warned, however, that U.S. East Coast beaches should still watch out in the coming week for large swells generated by Katia that could cause life-threatening coastal surf and rip currents.
By late Monday evening, Katia's winds had strengthened to 135 miles per hour (215 kph), making it a Category 4 hurricane on the five-step Saffir-Simpson intensity scale as it tracked northwestward on a path over the ocean between Bermuda and the Caribbean, the Miami-based center said.
The storm was moving toward the northwest at about 10 mph (16 kph) and the hurricane center said it was expected to continue in this general direction through Wednesday.
The center said some fluctuations in strength were possible during the next 24 hours, followed by a slow weakening.
NHC hurricane specialist Robbie Berg told Reuters the greatest threat from Katia for the U.S. eastern seaboard was likely to be the large swells and resulting dangerous coastal surf and currents the storm generated on its path.
"Even though these storms may stay offshore, they still can be a deadly threat, especially to people going to the beach," Berg said. "It may be a beautiful nice day out and you may just not know that there are rip currents there that can pull you out to sea," he added.
Forecasters and residents of the U.S. Atlantic seaboard have been keeping an anxious eye on Katia after Hurricane Irene raked up the East Coast from the Carolinas to Maine last weekend. It killed at least 40 people and caused extensive flooding, especially in New Jersey and Vermont.
Katia, the second hurricane of the June-through-November Atlantic season, has kept forecasters guessing for days about its potential threat to the United States.
Berg said the latest five-day forecast predicted the hurricane would swing north and then northeastward from Thursday in between Bermuda and the U.S. mainland, pushed away from the East Coast by a developing low pressure trough.
That would guide the storm around a ridge of high pressure in the central Atlantic known as the Bermuda High.
"The steering flow right now is pushing the storm to the northwest but once it gets closer to the East Coast, it'll start feeling the effects of that trough a little bit more, and it's going to make that sharp turn around the Bermuda High and head out northeastward over the open Atlantic," Berg said.
Another tropical wave moving westward
At 10 p.m. (0200 GMT Tuesday), Katia's center was located a bout 450 miles (725 km) south of Bermuda, the mid-Atlantic British overseas territory that despite its small size is a global reinsurance hub.
Berg said there was still a one in 10 chance parts of the East Coast could experience tropical storm-force winds when Katia passed well offshore later this week, especially jutting coastal areas like North Carolina's Outer Banks and Cape Cod in Massachusetts. Bermuda could also experience such winds.
Elsewhere, Tropical Storm Lee tested New Orleans' flood defenses over the weekend, and on Monday its weakened remnants threatened to dump heavy rain on states from Texas to Florida.
The Sept. 10 peak of the annual Atlantic hurricane season is approaching, and hurricane spotters were already watching another tropical wave, located southwest of the Cape Verde Islands off Africa.
That was moving westward and the NHC gave it a "high" chance of becoming a tropical cyclone in the next 48 hours.
Forecasters have predicted a very active 2011 Atlantic season with between eight and 10 hurricanes, above the long-term June to November average of six to seven hurricanes.
ReutersLast Mod: 06 Eylül 2011, 10:22