By Jeanine Prezioso and Janet McGurty
NEW YORK (Reuters) - Hurricane Irene left nearly 650,000 people without power in the U.S. Southeast on Saturday and energy firms braced for potentially much larger disruptions as the storm churns up the coast.
As the category 1 storm moved northward, utility firms warned of more blackouts ahead. Oil refineries, pipelines and fuel terminals limited operations to ensure safety, and the Coast Guard closely monitored energy shipping ports but kept the key hub at New York Harbor open for now.
Power went out in large swaths of Virginia and North Carolina after Irene pounded the coast and forced the Brunswick nuclear power plant to scale back generation, although the plant sustained no damage.
Electricity from two nuclear reactors at the 1,875-megawatt Southport-based plant was cut by 35 percent, to ensure the units can keep running if the storm affects other parts of the electric grid, said plant operator Progress Energy.
The utility said 269,000 customers were without power in North Carolina. Dominion Resources said 380,000 of its customers lost power in North Carolina and Virginia.
In New York City, which is bracing for Irene's impact late on Saturday into Sunday, intermittent rains began in the afternoon but the power grid has sustained little disruption so far. Utility Consolidated Edison said it doesn't plan to shut down the city's power ahead of Irene, although it may impose some power cuts early Sunday in low-lying downtown Manhattan, where flooding threats are higher.
U.S. Homeland Security Secretary Janet Napolitano on Friday warned of extensive power outages from Hurricane Irene.
The storm howled ashore in North Carolina on Saturday, weakening to a Category 1 hurricane and was expected to hit the mid-Atlantic states on Saturday night and New England on Sunday.
OIL AND GAS OPERATIONS
Some oil refineries in the U.S. Northeast -- home to 1.2 million barrels per day of capacity -- scaled back operations as a precaution, and pipeline operators warned of potential delays for fuel distribution ahead.
ConocoPhillips has cut rates at its 185,000 barrel per day (bpd) Trainer, Pennsylvania, refinery, sources said on Saturday. On Friday, rates had been cut by 25 percent at Sunoco's Marcus Hook plant in Pennsylvania, sources said.
The New York Harbor, a major hub for deliveries of crude oil and fuels by pipeline, barge and ship, remained open on Saturday.
The largest U.S. refined oil product pipeline, the 2.37 million bpd Colonial that runs from the Gulf Coast to New York, continued operating but warned of potential disruptions to customers along its path after several coastal oil terminals were forced to shut.
Although storm-related shipping interruptions could delay oil deliveries to the East Coast, or PADD 1, the region's plentiful crude and fuel inventories lessen the risk of any major supply shortages.
Trade group National Petrochemical and Refiners Association said on Friday that the region's oil terminals held 23 days of gasoline supply and 46 days supply of diesel and heating oil.
Around nine days of crude supply were held in the region's terminals, according to Energy Department data from last week.
(Reporting by Janet McGurty, Jeanine Prezioso, David Sheppard and Selam Gebrekidan; Writing by Joshua Schneyer; Editing by Jackie Frank and Matthew Robinson)